Documentation/DocBook/libata.tmpl

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   4
   5 <book id="libataDevGuide">
   6  <bookinfo>
   7   <title>libATA Developer's Guide</title>
   8
   9   <authorgroup>
  10    <author>
  11     <firstname>Jeff</firstname>
  12     <surname>Garzik</surname>
  13    </author>
  14   </authorgroup>
  15
  16   <copyright>
  17    <year>2003-2006</year>
  18    <holder>Jeff Garzik</holder>
  19   </copyright>
  20
  21   <legalnotice>
  22    <para>
  23    The contents of this file are subject to the Open
  24    Software License version 1.1 that can be found at
  25    <ulink url="http://fedoraproject.org/wiki/Licensing:OSL1.1">http://fedoraproject.org/wiki/Licensing:OSL1.1</ulink>
  26    and is included herein by reference.
  27    </para>
  28
  29    <para>
  30    Alternatively, the contents of this file may be used under the terms
  31    of the GNU General Public License version 2 (the "GPL") as distributed
  32    in the kernel source COPYING file, in which case the provisions of
  33    the GPL are applicable instead of the above.  If you wish to allow
  34    the use of your version of this file only under the terms of the
  35    GPL and not to allow others to use your version of this file under
  36    the OSL, indicate your decision by deleting the provisions above and
  37    replace them with the notice and other provisions required by the GPL.
  38    If you do not delete the provisions above, a recipient may use your
  39    version of this file under either the OSL or the GPL.
  40    </para>
  41
  42   </legalnotice>
  43  </bookinfo>
  44
  45 <toc></toc>
  46
  47   <chapter id="libataIntroduction">
  48      <title>Introduction</title>
  49   <para>
  50   libATA is a library used inside the Linux kernel to support ATA host
  51   controllers and devices.  libATA provides an ATA driver API, class
  52   transports for ATA and ATAPI devices, and SCSI&lt;-&gt;ATA translation
  53   for ATA devices according to the T10 SAT specification.
  54   </para>
  55   <para>
  56   This Guide documents the libATA driver API, library functions, library
  57   internals, and a couple sample ATA low-level drivers.
  58   </para>
  59   </chapter>
  60
  61   <chapter id="libataDriverApi">
  62      <title>libata Driver API</title>
  63      <para>
  64      struct ata_port_operations is defined for every low-level libata
  65      hardware driver, and it controls how the low-level driver
  66      interfaces with the ATA and SCSI layers.
  67      </para>
  68      <para>
  69      FIS-based drivers will hook into the system with ->qc_prep() and
  70      ->qc_issue() high-level hooks.  Hardware which behaves in a manner
  71      similar to PCI IDE hardware may utilize several generic helpers,
  72      defining at a bare minimum the bus I/O addresses of the ATA shadow
  73      register blocks.
  74      </para>
  75      <sect1>
  76         <title>struct ata_port_operations</title>
  77
  78         <sect2><title>Disable ATA port</title>
  79         <programlisting>
  80 void (*port_disable) (struct ata_port *);
  81         </programlisting>
  82
  83         <para>
  84         Called from ata_bus_probe() error path, as well as when
  85         unregistering from the SCSI module (rmmod, hot unplug).
  86         This function should do whatever needs to be done to take the
  87         port out of use.  In most cases, ata_port_disable() can be used
  88         as this hook.
  89         </para>
  90         <para>
  91         Called from ata_bus_probe() on a failed probe.
  92         Called from ata_scsi_release().
  93         </para>
  94
  95         </sect2>
  96
  97         <sect2><title>Post-IDENTIFY device configuration</title>
  98         <programlisting>
  99 void (*dev_config) (struct ata_port *, struct ata_device *);
 100         </programlisting>
 101
 102         <para>
 103         Called after IDENTIFY [PACKET] DEVICE is issued to each device
 104         found.  Typically used to apply device-specific fixups prior to
 105         issue of SET FEATURES - XFER MODE, and prior to operation.
 106         </para>
 107         <para>
 108         This entry may be specified as NULL in ata_port_operations.
 109         </para>
 110
 111         </sect2>
 112
 113         <sect2><title>Set PIO/DMA mode</title>
 114         <programlisting>
 115 void (*set_piomode) (struct ata_port *, struct ata_device *);
 116 void (*set_dmamode) (struct ata_port *, struct ata_device *);
 117 void (*post_set_mode) (struct ata_port *);
 118 unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int);
 119         </programlisting>
 120
 121         <para>
 122         Hooks called prior to the issue of SET FEATURES - XFER MODE
 123         command.  The optional ->mode_filter() hook is called when libata
 124         has built a mask of the possible modes. This is passed to the
 125         ->mode_filter() function which should return a mask of valid modes
 126         after filtering those unsuitable due to hardware limits. It is not
 127         valid to use this interface to add modes.
 128         </para>
 129         <para>
 130         dev->pio_mode and dev->dma_mode are guaranteed to be valid when
 131         ->set_piomode() and when ->set_dmamode() is called. The timings for
 132         any other drive sharing the cable will also be valid at this point.
 133         That is the library records the decisions for the modes of each
 134         drive on a channel before it attempts to set any of them.
 135         </para>
 136         <para>
 137         ->post_set_mode() is
 138         called unconditionally, after the SET FEATURES - XFER MODE
 139         command completes successfully.
 140         </para>
 141
 142         <para>
 143         ->set_piomode() is always called (if present), but
 144         ->set_dma_mode() is only called if DMA is possible.
 145         </para>
 146
 147         </sect2>
 148
 149         <sect2><title>Taskfile read/write</title>
 150         <programlisting>
 151 void (*sff_tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
 152 void (*sff_tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
 153         </programlisting>
 154
 155         <para>
 156         ->tf_load() is called to load the given taskfile into hardware
 157         registers / DMA buffers.  ->tf_read() is called to read the
 158         hardware registers / DMA buffers, to obtain the current set of
 159         taskfile register values.
 160         Most drivers for taskfile-based hardware (PIO or MMIO) use
 161         ata_sff_tf_load() and ata_sff_tf_read() for these hooks.
 162         </para>
 163
 164         </sect2>
 165
 166         <sect2><title>PIO data read/write</title>
 167         <programlisting>
 168 void (*sff_data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
 169         </programlisting>
 170
 171         <para>
 172 All bmdma-style drivers must implement this hook.  This is the low-level
 173 operation that actually copies the data bytes during a PIO data
 174 transfer.
 175 Typically the driver will choose one of ata_sff_data_xfer_noirq(),
 176 ata_sff_data_xfer(), or ata_sff_data_xfer32().
 177         </para>
 178
 179         </sect2>
 180
 181         <sect2><title>ATA command execute</title>
 182         <programlisting>
 183 void (*sff_exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
 184         </programlisting>
 185
 186         <para>
 187         causes an ATA command, previously loaded with
 188         ->tf_load(), to be initiated in hardware.
 189         Most drivers for taskfile-based hardware use ata_sff_exec_command()
 190         for this hook.
 191         </para>
 192
 193         </sect2>
 194
 195         <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
 196         <programlisting>
 197 int (*check_atapi_dma) (struct ata_queued_cmd *qc);
 198         </programlisting>
 199
 200         <para>
 201 Allow low-level driver to filter ATA PACKET commands, returning a status
 202 indicating whether or not it is OK to use DMA for the supplied PACKET
 203 command.
 204         </para>
 205         <para>
 206         This hook may be specified as NULL, in which case libata will
 207         assume that atapi dma can be supported.
 208         </para>
 209
 210         </sect2>
 211
 212         <sect2><title>Read specific ATA shadow registers</title>
 213         <programlisting>
 214 u8   (*sff_check_status)(struct ata_port *ap);
 215 u8   (*sff_check_altstatus)(struct ata_port *ap);
 216         </programlisting>
 217
 218         <para>
 219         Reads the Status/AltStatus ATA shadow register from
 220         hardware.  On some hardware, reading the Status register has
 221         the side effect of clearing the interrupt condition.
 222         Most drivers for taskfile-based hardware use
 223         ata_sff_check_status() for this hook.
 224         </para>
 225
 226         </sect2>
 227
 228         <sect2><title>Write specific ATA shadow register</title>
 229         <programlisting>
 230 void (*sff_set_devctl)(struct ata_port *ap, u8 ctl);
 231         </programlisting>
 232
 233         <para>
 234         Write the device control ATA shadow register to the hardware.
 235         Most drivers don't need to define this.
 236         </para>
 237
 238         </sect2>
 239
 240         <sect2><title>Select ATA device on bus</title>
 241         <programlisting>
 242 void (*sff_dev_select)(struct ata_port *ap, unsigned int device);
 243         </programlisting>
 244
 245         <para>
 246         Issues the low-level hardware command(s) that causes one of N
 247         hardware devices to be considered 'selected' (active and
 248         available for use) on the ATA bus.  This generally has no
 249         meaning on FIS-based devices.
 250         </para>
 251         <para>
 252         Most drivers for taskfile-based hardware use
 253         ata_sff_dev_select() for this hook.
 254         </para>
 255
 256         </sect2>
 257
 258         <sect2><title>Private tuning method</title>
 259         <programlisting>
 260 void (*set_mode) (struct ata_port *ap);
 261         </programlisting>
 262
 263         <para>
 264         By default libata performs drive and controller tuning in
 265         accordance with the ATA timing rules and also applies blacklists
 266         and cable limits. Some controllers need special handling and have
 267         custom tuning rules, typically raid controllers that use ATA
 268         commands but do not actually do drive timing.
 269         </para>
 270
 271         <warning>
 272         <para>
 273         This hook should not be used to replace the standard controller
 274         tuning logic when a controller has quirks. Replacing the default
 275         tuning logic in that case would bypass handling for drive and
 276         bridge quirks that may be important to data reliability. If a
 277         controller needs to filter the mode selection it should use the
 278         mode_filter hook instead.
 279         </para>
 280         </warning>
 281
 282         </sect2>
 283
 284         <sect2><title>Control PCI IDE BMDMA engine</title>
 285         <programlisting>
 286 void (*bmdma_setup) (struct ata_queued_cmd *qc);
 287 void (*bmdma_start) (struct ata_queued_cmd *qc);
 288 void (*bmdma_stop) (struct ata_port *ap);
 289 u8   (*bmdma_status) (struct ata_port *ap);
 290         </programlisting>
 291
 292         <para>
 293 When setting up an IDE BMDMA transaction, these hooks arm
 294 (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
 295 the hardware's DMA engine.  ->bmdma_status is used to read the standard
 296 PCI IDE DMA Status register.
 297         </para>
 298
 299         <para>
 300 These hooks are typically either no-ops, or simply not implemented, in
 301 FIS-based drivers.
 302         </para>
 303         <para>
 304 Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
 305 hook.  ata_bmdma_setup() will write the pointer to the PRD table to
 306 the IDE PRD Table Address register, enable DMA in the DMA Command
 307 register, and call exec_command() to begin the transfer.
 308         </para>
 309         <para>
 310 Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
 311 hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
 312 Command register.
 313         </para>
 314         <para>
 315 Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
 316 hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
 317 command register.
 318         </para>
 319         <para>
 320 Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
 321         </para>
 322
 323         </sect2>
 324
 325         <sect2><title>High-level taskfile hooks</title>
 326         <programlisting>
 327 void (*qc_prep) (struct ata_queued_cmd *qc);
 328 int (*qc_issue) (struct ata_queued_cmd *qc);
 329         </programlisting>
 330
 331         <para>
 332         Higher-level hooks, these two hooks can potentially supercede
 333         several of the above taskfile/DMA engine hooks.  ->qc_prep is
 334         called after the buffers have been DMA-mapped, and is typically
 335         used to populate the hardware's DMA scatter-gather table.
 336         Most drivers use the standard ata_qc_prep() helper function, but
 337         more advanced drivers roll their own.
 338         </para>
 339         <para>
 340         ->qc_issue is used to make a command active, once the hardware
 341         and S/G tables have been prepared.  IDE BMDMA drivers use the
 342         helper function ata_qc_issue_prot() for taskfile protocol-based
 343         dispatch.  More advanced drivers implement their own ->qc_issue.
 344         </para>
 345         <para>
 346         ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
 347         ->bmdma_start() as necessary to initiate a transfer.
 348         </para>
 349
 350         </sect2>
 351
 352         <sect2><title>Exception and probe handling (EH)</title>
 353         <programlisting>
 354 void (*eng_timeout) (struct ata_port *ap);
 355 void (*phy_reset) (struct ata_port *ap);
 356         </programlisting>
 357
 358         <para>
 359 Deprecated.  Use ->error_handler() instead.
 360         </para>
 361
 362         <programlisting>
 363 void (*freeze) (struct ata_port *ap);
 364 void (*thaw) (struct ata_port *ap);
 365         </programlisting>
 366
 367         <para>
 368 ata_port_freeze() is called when HSM violations or some other
 369 condition disrupts normal operation of the port.  A frozen port
 370 is not allowed to perform any operation until the port is
 371 thawed, which usually follows a successful reset.
 372         </para>
 373
 374         <para>
 375 The optional ->freeze() callback can be used for freezing the port
 376 hardware-wise (e.g. mask interrupt and stop DMA engine).  If a
 377 port cannot be frozen hardware-wise, the interrupt handler
 378 must ack and clear interrupts unconditionally while the port
 379 is frozen.
 380         </para>
 381         <para>
 382 The optional ->thaw() callback is called to perform the opposite of ->freeze():
 383 prepare the port for normal operation once again.  Unmask interrupts,
 384 start DMA engine, etc.
 385         </para>
 386
 387         <programlisting>
 388 void (*error_handler) (struct ata_port *ap);
 389         </programlisting>
 390
 391         <para>
 392 ->error_handler() is a driver's hook into probe, hotplug, and recovery
 393 and other exceptional conditions.  The primary responsibility of an
 394 implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set
 395 of EH hooks as arguments:
 396         </para>
 397
 398         <para>
 399 'prereset' hook (may be NULL) is called during an EH reset, before any other actions
 400 are taken.
 401         </para>
 402
 403         <para>
 404 'postreset' hook (may be NULL) is called after the EH reset is performed.  Based on
 405 existing conditions, severity of the problem, and hardware capabilities,
 406         </para>
 407
 408         <para>
 409 Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be
 410 called to perform the low-level EH reset.
 411         </para>
 412
 413         <programlisting>
 414 void (*post_internal_cmd) (struct ata_queued_cmd *qc);
 415         </programlisting>
 416
 417         <para>
 418 Perform any hardware-specific actions necessary to finish processing
 419 after executing a probe-time or EH-time command via ata_exec_internal().
 420         </para>
 421
 422         </sect2>
 423
 424         <sect2><title>Hardware interrupt handling</title>
 425         <programlisting>
 426 irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
 427 void (*irq_clear) (struct ata_port *);
 428         </programlisting>
 429
 430         <para>
 431         ->irq_handler is the interrupt handling routine registered with
 432         the system, by libata.  ->irq_clear is called during probe just
 433         before the interrupt handler is registered, to be sure hardware
 434         is quiet.
 435         </para>
 436         <para>
 437         The second argument, dev_instance, should be cast to a pointer
 438         to struct ata_host_set.
 439         </para>
 440         <para>
 441         Most legacy IDE drivers use ata_sff_interrupt() for the
 442         irq_handler hook, which scans all ports in the host_set,
 443         determines which queued command was active (if any), and calls
 444         ata_sff_host_intr(ap,qc).
 445         </para>
 446         <para>
 447         Most legacy IDE drivers use ata_sff_irq_clear() for the
 448         irq_clear() hook, which simply clears the interrupt and error
 449         flags in the DMA status register.
 450         </para>
 451
 452         </sect2>
 453
 454         <sect2><title>SATA phy read/write</title>
 455         <programlisting>
 456 int (*scr_read) (struct ata_port *ap, unsigned int sc_reg,
 457                  u32 *val);
 458 int (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
 459                    u32 val);
 460         </programlisting>
 461
 462         <para>
 463         Read and write standard SATA phy registers.  Currently only used
 464         if ->phy_reset hook called the sata_phy_reset() helper function.
 465         sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
 466         </para>
 467
 468         </sect2>
 469
 470         <sect2><title>Init and shutdown</title>
 471         <programlisting>
 472 int (*port_start) (struct ata_port *ap);
 473 void (*port_stop) (struct ata_port *ap);
 474 void (*host_stop) (struct ata_host_set *host_set);
 475         </programlisting>
 476
 477         <para>
 478         ->port_start() is called just after the data structures for each
 479         port are initialized.  Typically this is used to alloc per-port
 480         DMA buffers / tables / rings, enable DMA engines, and similar
 481         tasks.  Some drivers also use this entry point as a chance to
 482         allocate driver-private memory for ap->private_data.
 483         </para>
 484         <para>
 485         Many drivers use ata_port_start() as this hook or call
 486         it from their own port_start() hooks.  ata_port_start()
 487         allocates space for a legacy IDE PRD table and returns.
 488         </para>
 489         <para>
 490         ->port_stop() is called after ->host_stop().  Its sole function
 491         is to release DMA/memory resources, now that they are no longer
 492         actively being used.  Many drivers also free driver-private
 493         data from port at this time.
 494         </para>
 495         <para>
 496         ->host_stop() is called after all ->port_stop() calls
 497 have completed.  The hook must finalize hardware shutdown, release DMA
 498 and other resources, etc.
 499         This hook may be specified as NULL, in which case it is not called.
 500         </para>
 501
 502         </sect2>
 503
 504      </sect1>
 505   </chapter>
 506
 507   <chapter id="libataEH">
 508         <title>Error handling</title>
 509
 510         <para>
 511         This chapter describes how errors are handled under libata.
 512         Readers are advised to read SCSI EH
 513         (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first.
 514         </para>
 515
 516         <sect1><title>Origins of commands</title>
 517         <para>
 518         In libata, a command is represented with struct ata_queued_cmd
 519         or qc.  qc's are preallocated during port initialization and
 520         repetitively used for command executions.  Currently only one
 521         qc is allocated per port but yet-to-be-merged NCQ branch
 522         allocates one for each tag and maps each qc to NCQ tag 1-to-1.
 523         </para>
 524         <para>
 525         libata commands can originate from two sources - libata itself
 526         and SCSI midlayer.  libata internal commands are used for
 527         initialization and error handling.  All normal blk requests
 528         and commands for SCSI emulation are passed as SCSI commands
 529         through queuecommand callback of SCSI host template.
 530         </para>
 531         </sect1>
 532
 533         <sect1><title>How commands are issued</title>
 534
 535         <variablelist>
 536
 537         <varlistentry><term>Internal commands</term>
 538         <listitem>
 539         <para>
 540         First, qc is allocated and initialized using
 541         ata_qc_new_init().  Although ata_qc_new_init() doesn't
 542         implement any wait or retry mechanism when qc is not
 543         available, internal commands are currently issued only during
 544         initialization and error recovery, so no other command is
 545         active and allocation is guaranteed to succeed.
 546         </para>
 547         <para>
 548         Once allocated qc's taskfile is initialized for the command to
 549         be executed.  qc currently has two mechanisms to notify
 550         completion.  One is via qc->complete_fn() callback and the
 551         other is completion qc->waiting.  qc->complete_fn() callback
 552         is the asynchronous path used by normal SCSI translated
 553         commands and qc->waiting is the synchronous (issuer sleeps in
 554         process context) path used by internal commands.
 555         </para>
 556         <para>
 557         Once initialization is complete, host_set lock is acquired
 558         and the qc is issued.
 559         </para>
 560         </listitem>
 561         </varlistentry>
 562
 563         <varlistentry><term>SCSI commands</term>
 564         <listitem>
 565         <para>
 566         All libata drivers use ata_scsi_queuecmd() as
 567         hostt->queuecommand callback.  scmds can either be simulated
 568         or translated.  No qc is involved in processing a simulated
 569         scmd.  The result is computed right away and the scmd is
 570         completed.
 571         </para>
 572         <para>
 573         For a translated scmd, ata_qc_new_init() is invoked to
 574         allocate a qc and the scmd is translated into the qc.  SCSI
 575         midlayer's completion notification function pointer is stored
 576         into qc->scsidone.
 577         </para>
 578         <para>
 579         qc->complete_fn() callback is used for completion
 580         notification.  ATA commands use ata_scsi_qc_complete() while
 581         ATAPI commands use atapi_qc_complete().  Both functions end up
 582         calling qc->scsidone to notify upper layer when the qc is
 583         finished.  After translation is completed, the qc is issued
 584         with ata_qc_issue().
 585         </para>
 586         <para>
 587         Note that SCSI midlayer invokes hostt->queuecommand while
 588         holding host_set lock, so all above occur while holding
 589         host_set lock.
 590         </para>
 591         </listitem>
 592         </varlistentry>
 593
 594         </variablelist>
 595         </sect1>
 596
 597         <sect1><title>How commands are processed</title>
 598         <para>
 599         Depending on which protocol and which controller are used,
 600         commands are processed differently.  For the purpose of
 601         discussion, a controller which uses taskfile interface and all
 602         standard callbacks is assumed.
 603         </para>
 604         <para>
 605         Currently 6 ATA command protocols are used.  They can be
 606         sorted into the following four categories according to how
 607         they are processed.
 608         </para>
 609
 610         <variablelist>
 611            <varlistentry><term>ATA NO DATA or DMA</term>
 612            <listitem>
 613            <para>
 614            ATA_PROT_NODATA and ATA_PROT_DMA fall into this category.
 615            These types of commands don't require any software
 616            intervention once issued.  Device will raise interrupt on
 617            completion.
 618            </para>
 619            </listitem>
 620            </varlistentry>
 621
 622            <varlistentry><term>ATA PIO</term>
 623            <listitem>
 624            <para>
 625            ATA_PROT_PIO is in this category.  libata currently
 626            implements PIO with polling.  ATA_NIEN bit is set to turn
 627            off interrupt and pio_task on ata_wq performs polling and
 628            IO.
 629            </para>
 630            </listitem>
 631            </varlistentry>
 632
 633            <varlistentry><term>ATAPI NODATA or DMA</term>
 634            <listitem>
 635            <para>
 636            ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this
 637            category.  packet_task is used to poll BSY bit after
 638            issuing PACKET command.  Once BSY is turned off by the
 639            device, packet_task transfers CDB and hands off processing
 640            to interrupt handler.
 641            </para>
 642            </listitem>
 643            </varlistentry>
 644
 645            <varlistentry><term>ATAPI PIO</term>
 646            <listitem>
 647            <para>
 648            ATA_PROT_ATAPI is in this category.  ATA_NIEN bit is set
 649            and, as in ATAPI NODATA or DMA, packet_task submits cdb.
 650            However, after submitting cdb, further processing (data
 651            transfer) is handed off to pio_task.
 652            </para>
 653            </listitem>
 654            </varlistentry>
 655         </variablelist>
 656         </sect1>
 657
 658         <sect1><title>How commands are completed</title>
 659         <para>
 660         Once issued, all qc's are either completed with
 661         ata_qc_complete() or time out.  For commands which are handled
 662         by interrupts, ata_host_intr() invokes ata_qc_complete(), and,
 663         for PIO tasks, pio_task invokes ata_qc_complete().  In error
 664         cases, packet_task may also complete commands.
 665         </para>
 666         <para>
 667         ata_qc_complete() does the following.
 668         </para>
 669
 670         <orderedlist>
 671
 672         <listitem>
 673         <para>
 674         DMA memory is unmapped.
 675         </para>
 676         </listitem>
 677
 678         <listitem>
 679         <para>
 680         ATA_QCFLAG_ACTIVE is clared from qc->flags.
 681         </para>
 682         </listitem>
 683
 684         <listitem>
 685         <para>
 686         qc->complete_fn() callback is invoked.  If the return value of
 687         the callback is not zero.  Completion is short circuited and
 688         ata_qc_complete() returns.
 689         </para>
 690         </listitem>
 691
 692         <listitem>
 693         <para>
 694         __ata_qc_complete() is called, which does
 695            <orderedlist>
 696
 697            <listitem>
 698            <para>
 699            qc->flags is cleared to zero.
 700            </para>
 701            </listitem>
 702
 703            <listitem>
 704            <para>
 705            ap->active_tag and qc->tag are poisoned.
 706            </para>
 707            </listitem>
 708
 709            <listitem>
 710            <para>
 711            qc->waiting is claread &amp; completed (in that order).
 712            </para>
 713            </listitem>
 714
 715            <listitem>
 716            <para>
 717            qc is deallocated by clearing appropriate bit in ap->qactive.
 718            </para>
 719            </listitem>
 720
 721            </orderedlist>
 722         </para>
 723         </listitem>
 724
 725         </orderedlist>
 726
 727         <para>
 728         So, it basically notifies upper layer and deallocates qc.  One
 729         exception is short-circuit path in #3 which is used by
 730         atapi_qc_complete().
 731         </para>
 732         <para>
 733         For all non-ATAPI commands, whether it fails or not, almost
 734         the same code path is taken and very little error handling
 735         takes place.  A qc is completed with success status if it
 736         succeeded, with failed status otherwise.
 737         </para>
 738         <para>
 739         However, failed ATAPI commands require more handling as
 740         REQUEST SENSE is needed to acquire sense data.  If an ATAPI
 741         command fails, ata_qc_complete() is invoked with error status,
 742         which in turn invokes atapi_qc_complete() via
 743         qc->complete_fn() callback.
 744         </para>
 745         <para>
 746         This makes atapi_qc_complete() set scmd->result to
 747         SAM_STAT_CHECK_CONDITION, complete the scmd and return 1.  As
 748         the sense data is empty but scmd->result is CHECK CONDITION,
 749         SCSI midlayer will invoke EH for the scmd, and returning 1
 750         makes ata_qc_complete() to return without deallocating the qc.
 751         This leads us to ata_scsi_error() with partially completed qc.
 752         </para>
 753
 754         </sect1>
 755
 756         <sect1><title>ata_scsi_error()</title>
 757         <para>
 758         ata_scsi_error() is the current transportt->eh_strategy_handler()
 759         for libata.  As discussed above, this will be entered in two
 760         cases - timeout and ATAPI error completion.  This function
 761         calls low level libata driver's eng_timeout() callback, the
 762         standard callback for which is ata_eng_timeout().  It checks
 763         if a qc is active and calls ata_qc_timeout() on the qc if so.
 764         Actual error handling occurs in ata_qc_timeout().
 765         </para>
 766         <para>
 767         If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and
 768         completes the qc.  Note that as we're currently in EH, we
 769         cannot call scsi_done.  As described in SCSI EH doc, a
 770         recovered scmd should be either retried with
 771         scsi_queue_insert() or finished with scsi_finish_command().
 772         Here, we override qc->scsidone with scsi_finish_command() and
 773         calls ata_qc_complete().
 774         </para>
 775         <para>
 776         If EH is invoked due to a failed ATAPI qc, the qc here is
 777         completed but not deallocated.  The purpose of this
 778         half-completion is to use the qc as place holder to make EH
 779         code reach this place.  This is a bit hackish, but it works.
 780         </para>
 781         <para>
 782         Once control reaches here, the qc is deallocated by invoking
 783         __ata_qc_complete() explicitly.  Then, internal qc for REQUEST
 784         SENSE is issued.  Once sense data is acquired, scmd is
 785         finished by directly invoking scsi_finish_command() on the
 786         scmd.  Note that as we already have completed and deallocated
 787         the qc which was associated with the scmd, we don't need
 788         to/cannot call ata_qc_complete() again.
 789         </para>
 790
 791         </sect1>
 792
 793         <sect1><title>Problems with the current EH</title>
 794
 795         <itemizedlist>
 796
 797         <listitem>
 798         <para>
 799         Error representation is too crude.  Currently any and all
 800         error conditions are represented with ATA STATUS and ERROR
 801         registers.  Errors which aren't ATA device errors are treated
 802         as ATA device errors by setting ATA_ERR bit.  Better error
 803         descriptor which can properly represent ATA and other
 804         errors/exceptions is needed.
 805         </para>
 806         </listitem>
 807
 808         <listitem>
 809         <para>
 810         When handling timeouts, no action is taken to make device
 811         forget about the timed out command and ready for new commands.
 812         </para>
 813         </listitem>
 814
 815         <listitem>
 816         <para>
 817         EH handling via ata_scsi_error() is not properly protected
 818         from usual command processing.  On EH entrance, the device is
 819         not in quiescent state.  Timed out commands may succeed or
 820         fail any time.  pio_task and atapi_task may still be running.
 821         </para>
 822         </listitem>
 823
 824         <listitem>
 825         <para>
 826         Too weak error recovery.  Devices / controllers causing HSM
 827         mismatch errors and other errors quite often require reset to
 828         return to known state.  Also, advanced error handling is
 829         necessary to support features like NCQ and hotplug.
 830         </para>
 831         </listitem>
 832
 833         <listitem>
 834         <para>
 835         ATA errors are directly handled in the interrupt handler and
 836         PIO errors in pio_task.  This is problematic for advanced
 837         error handling for the following reasons.
 838         </para>
 839         <para>
 840         First, advanced error handling often requires context and
 841         internal qc execution.
 842         </para>
 843         <para>
 844         Second, even a simple failure (say, CRC error) needs
 845         information gathering and could trigger complex error handling
 846         (say, resetting &amp; reconfiguring).  Having multiple code
 847         paths to gather information, enter EH and trigger actions
 848         makes life painful.
 849         </para>
 850         <para>
 851         Third, scattered EH code makes implementing low level drivers
 852         difficult.  Low level drivers override libata callbacks.  If
 853         EH is scattered over several places, each affected callbacks
 854         should perform its part of error handling.  This can be error
 855         prone and painful.
 856         </para>
 857         </listitem>
 858
 859         </itemizedlist>
 860         </sect1>
 861   </chapter>
 862
 863   <chapter id="libataExt">
 864      <title>libata Library</title>
 865 !Edrivers/ata/libata-core.c
 866   </chapter>
 867
 868   <chapter id="libataInt">
 869      <title>libata Core Internals</title>
 870 !Idrivers/ata/libata-core.c
 871   </chapter>
 872
 873   <chapter id="libataScsiInt">
 874      <title>libata SCSI translation/emulation</title>
 875 !Edrivers/ata/libata-scsi.c
 876 !Idrivers/ata/libata-scsi.c
 877   </chapter>
 878
 879   <chapter id="ataExceptions">
 880      <title>ATA errors and exceptions</title>
 881
 882   <para>
 883   This chapter tries to identify what error/exception conditions exist
 884   for ATA/ATAPI devices and describe how they should be handled in
 885   implementation-neutral way.
 886   </para>
 887
 888   <para>
 889   The term 'error' is used to describe conditions where either an
 890   explicit error condition is reported from device or a command has
 891   timed out.
 892   </para>
 893
 894   <para>
 895   The term 'exception' is either used to describe exceptional
 896   conditions which are not errors (say, power or hotplug events), or
 897   to describe both errors and non-error exceptional conditions.  Where
 898   explicit distinction between error and exception is necessary, the
 899   term 'non-error exception' is used.
 900   </para>
 901
 902   <sect1 id="excat">
 903      <title>Exception categories</title>
 904      <para>
 905      Exceptions are described primarily with respect to legacy
 906      taskfile + bus master IDE interface.  If a controller provides
 907      other better mechanism for error reporting, mapping those into
 908      categories described below shouldn't be difficult.
 909      </para>
 910
 911      <para>
 912      In the following sections, two recovery actions - reset and
 913      reconfiguring transport - are mentioned.  These are described
 914      further in <xref linkend="exrec"/>.
 915      </para>
 916
 917      <sect2 id="excatHSMviolation">
 918         <title>HSM violation</title>
 919         <para>
 920         This error is indicated when STATUS value doesn't match HSM
 921         requirement during issuing or execution any ATA/ATAPI command.
 922         </para>
 923
 924         <itemizedlist>
 925         <title>Examples</title>
 926
 927         <listitem>
 928         <para>
 929         ATA_STATUS doesn't contain !BSY &amp;&amp; DRDY &amp;&amp; !DRQ while trying
 930         to issue a command.
 931         </para>
 932         </listitem>
 933
 934         <listitem>
 935         <para>
 936         !BSY &amp;&amp; !DRQ during PIO data transfer.
 937         </para>
 938         </listitem>
 939
 940         <listitem>
 941         <para>
 942         DRQ on command completion.
 943         </para>
 944         </listitem>
 945
 946         <listitem>
 947         <para>
 948         !BSY &amp;&amp; ERR after CDB transfer starts but before the
 949         last byte of CDB is transferred.  ATA/ATAPI standard states
 950         that &quot;The device shall not terminate the PACKET command
 951         with an error before the last byte of the command packet has
 952         been written&quot; in the error outputs description of PACKET
 953         command and the state diagram doesn't include such
 954         transitions.
 955         </para>
 956         </listitem>
 957
 958         </itemizedlist>
 959
 960         <para>
 961         In these cases, HSM is violated and not much information
 962         regarding the error can be acquired from STATUS or ERROR
 963         register.  IOW, this error can be anything - driver bug,
 964         faulty device, controller and/or cable.
 965         </para>
 966
 967         <para>
 968         As HSM is violated, reset is necessary to restore known state.
 969         Reconfiguring transport for lower speed might be helpful too
 970         as transmission errors sometimes cause this kind of errors.
 971         </para>
 972      </sect2>
 973
 974      <sect2 id="excatDevErr">
 975         <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title>
 976
 977         <para>
 978         These are errors detected and reported by ATA/ATAPI devices
 979         indicating device problems.  For this type of errors, STATUS
 980         and ERROR register values are valid and describe error
 981         condition.  Note that some of ATA bus errors are detected by
 982         ATA/ATAPI devices and reported using the same mechanism as
 983         device errors.  Those cases are described later in this
 984         section.
 985         </para>
 986
 987         <para>
 988         For ATA commands, this type of errors are indicated by !BSY
 989         &amp;&amp; ERR during command execution and on completion.
 990         </para>
 991
 992         <para>For ATAPI commands,</para>
 993
 994         <itemizedlist>
 995
 996         <listitem>
 997         <para>
 998         !BSY &amp;&amp; ERR &amp;&amp; ABRT right after issuing PACKET
 999         indicates that PACKET command is not supported and falls in
1000         this category.
1001         </para>
1002         </listitem>
1003
1004         <listitem>
1005         <para>
1006         !BSY &amp;&amp; ERR(==CHK) &amp;&amp; !ABRT after the last
1007         byte of CDB is transferred indicates CHECK CONDITION and
1008         doesn't fall in this category.
1009         </para>
1010         </listitem>
1011
1012         <listitem>
1013         <para>
1014         !BSY &amp;&amp; ERR(==CHK) &amp;&amp; ABRT after the last byte
1015         of CDB is transferred *probably* indicates CHECK CONDITION and
1016         doesn't fall in this category.
1017         </para>
1018         </listitem>
1019
1020         </itemizedlist>
1021
1022         <para>
1023         Of errors detected as above, the followings are not ATA/ATAPI
1024         device errors but ATA bus errors and should be handled
1025         according to <xref linkend="excatATAbusErr"/>.
1026         </para>
1027
1028         <variablelist>
1029
1030            <varlistentry>
1031            <term>CRC error during data transfer</term>
1032            <listitem>
1033            <para>
1034            This is indicated by ICRC bit in the ERROR register and
1035            means that corruption occurred during data transfer.  Up to
1036            ATA/ATAPI-7, the standard specifies that this bit is only
1037            applicable to UDMA transfers but ATA/ATAPI-8 draft revision
1038            1f says that the bit may be applicable to multiword DMA and
1039            PIO.
1040            </para>
1041            </listitem>
1042            </varlistentry>
1043
1044            <varlistentry>
1045            <term>ABRT error during data transfer or on completion</term>
1046            <listitem>
1047            <para>
1048            Up to ATA/ATAPI-7, the standard specifies that ABRT could be
1049            set on ICRC errors and on cases where a device is not able
1050            to complete a command.  Combined with the fact that MWDMA
1051            and PIO transfer errors aren't allowed to use ICRC bit up to
1052            ATA/ATAPI-7, it seems to imply that ABRT bit alone could
1053            indicate transfer errors.
1054            </para>
1055            <para>
1056            However, ATA/ATAPI-8 draft revision 1f removes the part
1057            that ICRC errors can turn on ABRT.  So, this is kind of
1058            gray area.  Some heuristics are needed here.
1059            </para>
1060            </listitem>
1061            </varlistentry>
1062
1063         </variablelist>
1064
1065         <para>
1066         ATA/ATAPI device errors can be further categorized as follows.
1067         </para>
1068
1069         <variablelist>
1070
1071            <varlistentry>
1072            <term>Media errors</term>
1073            <listitem>
1074            <para>
1075            This is indicated by UNC bit in the ERROR register.  ATA
1076            devices reports UNC error only after certain number of
1077            retries cannot recover the data, so there's nothing much
1078            else to do other than notifying upper layer.
1079            </para>
1080            <para>
1081            READ and WRITE commands report CHS or LBA of the first
1082            failed sector but ATA/ATAPI standard specifies that the
1083            amount of transferred data on error completion is
1084            indeterminate, so we cannot assume that sectors preceding
1085            the failed sector have been transferred and thus cannot
1086            complete those sectors successfully as SCSI does.
1087            </para>
1088            </listitem>
1089            </varlistentry>
1090
1091            <varlistentry>
1092            <term>Media changed / media change requested error</term>
1093            <listitem>
1094            <para>
1095            &lt;&lt;TODO: fill here&gt;&gt;
1096            </para>
1097            </listitem>
1098            </varlistentry>
1099
1100            <varlistentry><term>Address error</term>
1101            <listitem>
1102            <para>
1103            This is indicated by IDNF bit in the ERROR register.
1104            Report to upper layer.
1105            </para>
1106            </listitem>
1107            </varlistentry>
1108
1109            <varlistentry><term>Other errors</term>
1110            <listitem>
1111            <para>
1112            This can be invalid command or parameter indicated by ABRT
1113            ERROR bit or some other error condition.  Note that ABRT
1114            bit can indicate a lot of things including ICRC and Address
1115            errors.  Heuristics needed.
1116            </para>
1117            </listitem>
1118            </varlistentry>
1119
1120         </variablelist>
1121
1122         <para>
1123         Depending on commands, not all STATUS/ERROR bits are
1124         applicable.  These non-applicable bits are marked with
1125         &quot;na&quot; in the output descriptions but up to ATA/ATAPI-7
1126         no definition of &quot;na&quot; can be found.  However,
1127         ATA/ATAPI-8 draft revision 1f describes &quot;N/A&quot; as
1128         follows.
1129         </para>
1130
1131         <blockquote>
1132         <variablelist>
1133            <varlistentry><term>3.2.3.3a N/A</term>
1134            <listitem>
1135            <para>
1136            A keyword the indicates a field has no defined value in
1137            this standard and should not be checked by the host or
1138            device. N/A fields should be cleared to zero.
1139            </para>
1140            </listitem>
1141            </varlistentry>
1142         </variablelist>
1143         </blockquote>
1144
1145         <para>
1146         So, it seems reasonable to assume that &quot;na&quot; bits are
1147         cleared to zero by devices and thus need no explicit masking.
1148         </para>
1149
1150      </sect2>
1151
1152      <sect2 id="excatATAPIcc">
1153         <title>ATAPI device CHECK CONDITION</title>
1154
1155         <para>
1156         ATAPI device CHECK CONDITION error is indicated by set CHK bit
1157         (ERR bit) in the STATUS register after the last byte of CDB is
1158         transferred for a PACKET command.  For this kind of errors,
1159         sense data should be acquired to gather information regarding
1160         the errors.  REQUEST SENSE packet command should be used to
1161         acquire sense data.
1162         </para>
1163
1164         <para>
1165         Once sense data is acquired, this type of errors can be
1166         handled similary to other SCSI errors.  Note that sense data
1167         may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR
1168         &amp;&amp; ASC/ASCQ 47h/00h SCSI PARITY ERROR).  In such
1169         cases, the error should be considered as an ATA bus error and
1170         handled according to <xref linkend="excatATAbusErr"/>.
1171         </para>
1172
1173      </sect2>
1174
1175      <sect2 id="excatNCQerr">
1176         <title>ATA device error (NCQ)</title>
1177
1178         <para>
1179         NCQ command error is indicated by cleared BSY and set ERR bit
1180         during NCQ command phase (one or more NCQ commands
1181         outstanding).  Although STATUS and ERROR registers will
1182         contain valid values describing the error, READ LOG EXT is
1183         required to clear the error condition, determine which command
1184         has failed and acquire more information.
1185         </para>
1186
1187         <para>
1188         READ LOG EXT Log Page 10h reports which tag has failed and
1189         taskfile register values describing the error.  With this
1190         information the failed command can be handled as a normal ATA
1191         command error as in <xref linkend="excatDevErr"/> and all
1192         other in-flight commands must be retried.  Note that this
1193         retry should not be counted - it's likely that commands
1194         retried this way would have completed normally if it were not
1195         for the failed command.
1196         </para>
1197
1198         <para>
1199         Note that ATA bus errors can be reported as ATA device NCQ
1200         errors.  This should be handled as described in <xref
1201         linkend="excatATAbusErr"/>.
1202         </para>
1203
1204         <para>
1205         If READ LOG EXT Log Page 10h fails or reports NQ, we're
1206         thoroughly screwed.  This condition should be treated
1207         according to <xref linkend="excatHSMviolation"/>.
1208         </para>
1209
1210      </sect2>
1211
1212      <sect2 id="excatATAbusErr">
1213         <title>ATA bus error</title>
1214
1215         <para>
1216         ATA bus error means that data corruption occurred during
1217         transmission over ATA bus (SATA or PATA).  This type of errors
1218         can be indicated by
1219         </para>
1220
1221         <itemizedlist>
1222
1223         <listitem>
1224         <para>
1225         ICRC or ABRT error as described in <xref linkend="excatDevErr"/>.
1226         </para>
1227         </listitem>
1228
1229         <listitem>
1230         <para>
1231         Controller-specific error completion with error information
1232         indicating transmission error.
1233         </para>
1234         </listitem>
1235
1236         <listitem>
1237         <para>
1238         On some controllers, command timeout.  In this case, there may
1239         be a mechanism to determine that the timeout is due to
1240         transmission error.
1241         </para>
1242         </listitem>
1243
1244         <listitem>
1245         <para>
1246         Unknown/random errors, timeouts and all sorts of weirdities.
1247         </para>
1248         </listitem>
1249
1250         </itemizedlist>
1251
1252         <para>
1253         As described above, transmission errors can cause wide variety
1254         of symptoms ranging from device ICRC error to random device
1255         lockup, and, for many cases, there is no way to tell if an
1256         error condition is due to transmission error or not;
1257         therefore, it's necessary to employ some kind of heuristic
1258         when dealing with errors and timeouts.  For example,
1259         encountering repetitive ABRT errors for known supported
1260         command is likely to indicate ATA bus error.
1261         </para>
1262
1263         <para>
1264         Once it's determined that ATA bus errors have possibly
1265         occurred, lowering ATA bus transmission speed is one of
1266         actions which may alleviate the problem.  See <xref
1267         linkend="exrecReconf"/> for more information.
1268         </para>
1269
1270      </sect2>
1271
1272      <sect2 id="excatPCIbusErr">
1273         <title>PCI bus error</title>
1274
1275         <para>
1276         Data corruption or other failures during transmission over PCI
1277         (or other system bus).  For standard BMDMA, this is indicated
1278         by Error bit in the BMDMA Status register.  This type of
1279         errors must be logged as it indicates something is very wrong
1280         with the system.  Resetting host controller is recommended.
1281         </para>
1282
1283      </sect2>
1284
1285      <sect2 id="excatLateCompletion">
1286         <title>Late completion</title>
1287
1288         <para>
1289         This occurs when timeout occurs and the timeout handler finds
1290         out that the timed out command has completed successfully or
1291         with error.  This is usually caused by lost interrupts.  This
1292         type of errors must be logged.  Resetting host controller is
1293         recommended.
1294         </para>
1295
1296      </sect2>
1297
1298      <sect2 id="excatUnknown">
1299         <title>Unknown error (timeout)</title>
1300
1301         <para>
1302         This is when timeout occurs and the command is still
1303         processing or the host and device are in unknown state.  When
1304         this occurs, HSM could be in any valid or invalid state.  To
1305         bring the device to known state and make it forget about the
1306         timed out command, resetting is necessary.  The timed out
1307         command may be retried.
1308         </para>
1309
1310         <para>
1311         Timeouts can also be caused by transmission errors.  Refer to
1312         <xref linkend="excatATAbusErr"/> for more details.
1313         </para>
1314
1315      </sect2>
1316
1317      <sect2 id="excatHoplugPM">
1318         <title>Hotplug and power management exceptions</title>
1319
1320         <para>
1321         &lt;&lt;TODO: fill here&gt;&gt;
1322         </para>
1323
1324      </sect2>
1325
1326   </sect1>
1327
1328   <sect1 id="exrec">
1329      <title>EH recovery actions</title>
1330
1331      <para>
1332      This section discusses several important recovery actions.
1333      </para>
1334
1335      <sect2 id="exrecClr">
1336         <title>Clearing error condition</title>
1337
1338         <para>
1339         Many controllers require its error registers to be cleared by
1340         error handler.  Different controllers may have different
1341         requirements.
1342         </para>
1343
1344         <para>
1345         For SATA, it's strongly recommended to clear at least SError
1346         register during error handling.
1347         </para>
1348      </sect2>
1349
1350      <sect2 id="exrecRst">
1351         <title>Reset</title>
1352
1353         <para>
1354         During EH, resetting is necessary in the following cases.
1355         </para>
1356
1357         <itemizedlist>
1358
1359         <listitem>
1360         <para>
1361         HSM is in unknown or invalid state
1362         </para>
1363         </listitem>
1364
1365         <listitem>
1366         <para>
1367         HBA is in unknown or invalid state
1368         </para>
1369         </listitem>
1370
1371         <listitem>
1372         <para>
1373         EH needs to make HBA/device forget about in-flight commands
1374         </para>
1375         </listitem>
1376
1377         <listitem>
1378         <para>
1379         HBA/device behaves weirdly
1380         </para>
1381         </listitem>
1382
1383         </itemizedlist>
1384
1385         <para>
1386         Resetting during EH might be a good idea regardless of error
1387         condition to improve EH robustness.  Whether to reset both or
1388         either one of HBA and device depends on situation but the
1389         following scheme is recommended.
1390         </para>
1391
1392         <itemizedlist>
1393
1394         <listitem>
1395         <para>
1396         When it's known that HBA is in ready state but ATA/ATAPI
1397         device is in unknown state, reset only device.
1398         </para>
1399         </listitem>
1400
1401         <listitem>
1402         <para>
1403         If HBA is in unknown state, reset both HBA and device.
1404         </para>
1405         </listitem>
1406
1407         </itemizedlist>
1408
1409         <para>
1410         HBA resetting is implementation specific.  For a controller
1411         complying to taskfile/BMDMA PCI IDE, stopping active DMA
1412         transaction may be sufficient iff BMDMA state is the only HBA
1413         context.  But even mostly taskfile/BMDMA PCI IDE complying
1414         controllers may have implementation specific requirements and
1415         mechanism to reset themselves.  This must be addressed by
1416         specific drivers.
1417         </para>
1418
1419         <para>
1420         OTOH, ATA/ATAPI standard describes in detail ways to reset
1421         ATA/ATAPI devices.
1422         </para>
1423
1424         <variablelist>
1425
1426            <varlistentry><term>PATA hardware reset</term>
1427            <listitem>
1428            <para>
1429            This is hardware initiated device reset signalled with
1430            asserted PATA RESET- signal.  There is no standard way to
1431            initiate hardware reset from software although some
1432            hardware provides registers that allow driver to directly
1433            tweak the RESET- signal.
1434            </para>
1435            </listitem>
1436            </varlistentry>
1437
1438            <varlistentry><term>Software reset</term>
1439            <listitem>
1440            <para>
1441            This is achieved by turning CONTROL SRST bit on for at
1442            least 5us.  Both PATA and SATA support it but, in case of
1443            SATA, this may require controller-specific support as the
1444            second Register FIS to clear SRST should be transmitted
1445            while BSY bit is still set.  Note that on PATA, this resets
1446            both master and slave devices on a channel.
1447            </para>
1448            </listitem>
1449            </varlistentry>
1450
1451            <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term>
1452            <listitem>
1453            <para>
1454            Although ATA/ATAPI standard doesn't describe exactly, EDD
1455            implies some level of resetting, possibly similar level
1456            with software reset.  Host-side EDD protocol can be handled
1457            with normal command processing and most SATA controllers
1458            should be able to handle EDD's just like other commands.
1459            As in software reset, EDD affects both devices on a PATA
1460            bus.
1461            </para>
1462            <para>
1463            Although EDD does reset devices, this doesn't suit error
1464            handling as EDD cannot be issued while BSY is set and it's
1465            unclear how it will act when device is in unknown/weird
1466            state.
1467            </para>
1468            </listitem>
1469            </varlistentry>
1470
1471            <varlistentry><term>ATAPI DEVICE RESET command</term>
1472            <listitem>
1473            <para>
1474            This is very similar to software reset except that reset
1475            can be restricted to the selected device without affecting
1476            the other device sharing the cable.
1477            </para>
1478            </listitem>
1479            </varlistentry>
1480
1481            <varlistentry><term>SATA phy reset</term>
1482            <listitem>
1483            <para>
1484            This is the preferred way of resetting a SATA device.  In
1485            effect, it's identical to PATA hardware reset.  Note that
1486            this can be done with the standard SCR Control register.
1487            As such, it's usually easier to implement than software
1488            reset.
1489            </para>
1490            </listitem>
1491            </varlistentry>
1492
1493         </variablelist>
1494
1495         <para>
1496         One more thing to consider when resetting devices is that
1497         resetting clears certain configuration parameters and they
1498         need to be set to their previous or newly adjusted values
1499         after reset.
1500         </para>
1501
1502         <para>
1503         Parameters affected are.
1504         </para>
1505
1506         <itemizedlist>
1507
1508         <listitem>
1509         <para>
1510         CHS set up with INITIALIZE DEVICE PARAMETERS (seldom used)
1511         </para>
1512         </listitem>
1513
1514         <listitem>
1515         <para>
1516         Parameters set with SET FEATURES including transfer mode setting
1517         </para>
1518         </listitem>
1519
1520         <listitem>
1521         <para>
1522         Block count set with SET MULTIPLE MODE
1523         </para>
1524         </listitem>
1525
1526         <listitem>
1527         <para>
1528         Other parameters (SET MAX, MEDIA LOCK...)
1529         </para>
1530         </listitem>
1531
1532         </itemizedlist>
1533
1534         <para>
1535         ATA/ATAPI standard specifies that some parameters must be
1536         maintained across hardware or software reset, but doesn't
1537         strictly specify all of them.  Always reconfiguring needed
1538         parameters after reset is required for robustness.  Note that
1539         this also applies when resuming from deep sleep (power-off).
1540         </para>
1541
1542         <para>
1543         Also, ATA/ATAPI standard requires that IDENTIFY DEVICE /
1544         IDENTIFY PACKET DEVICE is issued after any configuration
1545         parameter is updated or a hardware reset and the result used
1546         for further operation.  OS driver is required to implement
1547         revalidation mechanism to support this.
1548         </para>
1549
1550      </sect2>
1551
1552      <sect2 id="exrecReconf">
1553         <title>Reconfigure transport</title>
1554
1555         <para>
1556         For both PATA and SATA, a lot of corners are cut for cheap
1557         connectors, cables or controllers and it's quite common to see
1558         high transmission error rate.  This can be mitigated by
1559         lowering transmission speed.
1560         </para>
1561
1562         <para>
1563         The following is a possible scheme Jeff Garzik suggested.
1564         </para>
1565
1566         <blockquote>
1567         <para>
1568         If more than $N (3?) transmission errors happen in 15 minutes,
1569         </para>
1570         <itemizedlist>
1571         <listitem>
1572         <para>
1573         if SATA, decrease SATA PHY speed.  if speed cannot be decreased,
1574         </para>
1575         </listitem>
1576         <listitem>
1577         <para>
1578         decrease UDMA xfer speed.  if at UDMA0, switch to PIO4,
1579         </para>
1580         </listitem>
1581         <listitem>
1582         <para>
1583         decrease PIO xfer speed.  if at PIO3, complain, but continue
1584         </para>
1585         </listitem>
1586         </itemizedlist>
1587         </blockquote>
1588
1589      </sect2>
1590
1591   </sect1>
1592
1593   </chapter>
1594
1595   <chapter id="PiixInt">
1596      <title>ata_piix Internals</title>
1597 !Idrivers/ata/ata_piix.c
1598   </chapter>
1599
1600   <chapter id="SILInt">
1601      <title>sata_sil Internals</title>
1602 !Idrivers/ata/sata_sil.c
1603   </chapter>
1604
1605   <chapter id="libataThanks">
1606      <title>Thanks</title>
1607   <para>
1608   The bulk of the ATA knowledge comes thanks to long conversations with
1609   Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
1610   and SCSI specifications.
1611   </para>
1612   <para>
1613   Thanks to Alan Cox for pointing out similarities
1614   between SATA and SCSI, and in general for motivation to hack on
1615   libata.
1616   </para>
1617   <para>
1618   libata's device detection
1619   method, ata_pio_devchk, and in general all the early probing was
1620   based on extensive study of Hale Landis's probe/reset code in his
1621   ATADRVR driver (www.ata-atapi.com).
1622   </para>
1623   </chapter>
1624
1625 </book>