Documentation/DocBook/libata.tmpl

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   2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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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>2003-2005</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://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein
  26    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() and ata_bus_reset() error paths,
  85         as well as when unregistering from the SCSI module (rmmod, hot
  86         unplug).
  87         This function should do whatever needs to be done to take the
  88         port out of use.  In most cases, ata_port_disable() can be used
  89         as this hook.
  90         </para>
  91         <para>
  92         Called from ata_bus_probe() on a failed probe.
  93         Called from ata_bus_reset() on a failed bus reset.
  94         Called from ata_scsi_release().
  95         </para>
  96
  97         </sect2>
  98
  99         <sect2><title>Post-IDENTIFY device configuration</title>
 100         <programlisting>
 101 void (*dev_config) (struct ata_port *, struct ata_device *);
 102         </programlisting>
 103
 104         <para>
 105         Called after IDENTIFY [PACKET] DEVICE is issued to each device
 106         found.  Typically used to apply device-specific fixups prior to
 107         issue of SET FEATURES - XFER MODE, and prior to operation.
 108         </para>
 109         <para>
 110         Called by ata_device_add() after ata_dev_identify() determines
 111         a device is present.
 112         </para>
 113         <para>
 114         This entry may be specified as NULL in ata_port_operations.
 115         </para>
 116
 117         </sect2>
 118
 119         <sect2><title>Set PIO/DMA mode</title>
 120         <programlisting>
 121 void (*set_piomode) (struct ata_port *, struct ata_device *);
 122 void (*set_dmamode) (struct ata_port *, struct ata_device *);
 123 void (*post_set_mode) (struct ata_port *);
 124 unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int);
 125         </programlisting>
 126
 127         <para>
 128         Hooks called prior to the issue of SET FEATURES - XFER MODE
 129         command.  The optional ->mode_filter() hook is called when libata
 130         has built a mask of the possible modes. This is passed to the
 131         ->mode_filter() function which should return a mask of valid modes
 132         after filtering those unsuitable due to hardware limits. It is not
 133         valid to use this interface to add modes.
 134         </para>
 135         <para>
 136         dev->pio_mode and dev->dma_mode are guaranteed to be valid when
 137         ->set_piomode() and when ->set_dmamode() is called. The timings for
 138         any other drive sharing the cable will also be valid at this point.
 139         That is the library records the decisions for the modes of each
 140         drive on a channel before it attempts to set any of them.
 141         </para>
 142         <para>
 143         ->post_set_mode() is
 144         called unconditionally, after the SET FEATURES - XFER MODE
 145         command completes successfully.
 146         </para>
 147
 148         <para>
 149         ->set_piomode() is always called (if present), but
 150         ->set_dma_mode() is only called if DMA is possible.
 151         </para>
 152
 153         </sect2>
 154
 155         <sect2><title>Taskfile read/write</title>
 156         <programlisting>
 157 void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
 158 void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
 159         </programlisting>
 160
 161         <para>
 162         ->tf_load() is called to load the given taskfile into hardware
 163         registers / DMA buffers.  ->tf_read() is called to read the
 164         hardware registers / DMA buffers, to obtain the current set of
 165         taskfile register values.
 166         Most drivers for taskfile-based hardware (PIO or MMIO) use
 167         ata_tf_load() and ata_tf_read() for these hooks.
 168         </para>
 169
 170         </sect2>
 171
 172         <sect2><title>ATA command execute</title>
 173         <programlisting>
 174 void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
 175         </programlisting>
 176
 177         <para>
 178         causes an ATA command, previously loaded with
 179         ->tf_load(), to be initiated in hardware.
 180         Most drivers for taskfile-based hardware use ata_exec_command()
 181         for this hook.
 182         </para>
 183
 184         </sect2>
 185
 186         <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
 187         <programlisting>
 188 int (*check_atapi_dma) (struct ata_queued_cmd *qc);
 189         </programlisting>
 190
 191         <para>
 192 Allow low-level driver to filter ATA PACKET commands, returning a status
 193 indicating whether or not it is OK to use DMA for the supplied PACKET
 194 command.
 195         </para>
 196         <para>
 197         This hook may be specified as NULL, in which case libata will
 198         assume that atapi dma can be supported.
 199         </para>
 200
 201         </sect2>
 202
 203         <sect2><title>Read specific ATA shadow registers</title>
 204         <programlisting>
 205 u8   (*check_status)(struct ata_port *ap);
 206 u8   (*check_altstatus)(struct ata_port *ap);
 207 u8   (*check_err)(struct ata_port *ap);
 208         </programlisting>
 209
 210         <para>
 211         Reads the Status/AltStatus/Error ATA shadow register from
 212         hardware.  On some hardware, reading the Status register has
 213         the side effect of clearing the interrupt condition.
 214         Most drivers for taskfile-based hardware use
 215         ata_check_status() for this hook.
 216         </para>
 217         <para>
 218         Note that because this is called from ata_device_add(), at
 219         least a dummy function that clears device interrupts must be
 220         provided for all drivers, even if the controller doesn't
 221         actually have a taskfile status register.
 222         </para>
 223
 224         </sect2>
 225
 226         <sect2><title>Select ATA device on bus</title>
 227         <programlisting>
 228 void (*dev_select)(struct ata_port *ap, unsigned int device);
 229         </programlisting>
 230
 231         <para>
 232         Issues the low-level hardware command(s) that causes one of N
 233         hardware devices to be considered 'selected' (active and
 234         available for use) on the ATA bus.  This generally has no
 235         meaning on FIS-based devices.
 236         </para>
 237         <para>
 238         Most drivers for taskfile-based hardware use
 239         ata_std_dev_select() for this hook.  Controllers which do not
 240         support second drives on a port (such as SATA contollers) will
 241         use ata_noop_dev_select().
 242         </para>
 243
 244         </sect2>
 245
 246         <sect2><title>Private tuning method</title>
 247         <programlisting>
 248 void (*set_mode) (struct ata_port *ap);
 249         </programlisting>
 250
 251         <para>
 252         By default libata performs drive and controller tuning in
 253         accordance with the ATA timing rules and also applies blacklists
 254         and cable limits. Some controllers need special handling and have
 255         custom tuning rules, typically raid controllers that use ATA
 256         commands but do not actually do drive timing.
 257         </para>
 258
 259         <warning>
 260         <para>
 261         This hook should not be used to replace the standard controller
 262         tuning logic when a controller has quirks. Replacing the default
 263         tuning logic in that case would bypass handling for drive and
 264         bridge quirks that may be important to data reliability. If a
 265         controller needs to filter the mode selection it should use the
 266         mode_filter hook instead.
 267         </para>
 268         </warning>
 269
 270         </sect2>
 271
 272         <sect2><title>Reset ATA bus</title>
 273         <programlisting>
 274 void (*phy_reset) (struct ata_port *ap);
 275         </programlisting>
 276
 277         <para>
 278         The very first step in the probe phase.  Actions vary depending
 279         on the bus type, typically.  After waking up the device and probing
 280         for device presence (PATA and SATA), typically a soft reset
 281         (SRST) will be performed.  Drivers typically use the helper
 282         functions ata_bus_reset() or sata_phy_reset() for this hook.
 283         Many SATA drivers use sata_phy_reset() or call it from within
 284         their own phy_reset() functions.
 285         </para>
 286
 287         </sect2>
 288
 289         <sect2><title>Control PCI IDE BMDMA engine</title>
 290         <programlisting>
 291 void (*bmdma_setup) (struct ata_queued_cmd *qc);
 292 void (*bmdma_start) (struct ata_queued_cmd *qc);
 293 void (*bmdma_stop) (struct ata_port *ap);
 294 u8   (*bmdma_status) (struct ata_port *ap);
 295         </programlisting>
 296
 297         <para>
 298 When setting up an IDE BMDMA transaction, these hooks arm
 299 (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
 300 the hardware's DMA engine.  ->bmdma_status is used to read the standard
 301 PCI IDE DMA Status register.
 302         </para>
 303
 304         <para>
 305 These hooks are typically either no-ops, or simply not implemented, in
 306 FIS-based drivers.
 307         </para>
 308         <para>
 309 Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
 310 hook.  ata_bmdma_setup() will write the pointer to the PRD table to
 311 the IDE PRD Table Address register, enable DMA in the DMA Command
 312 register, and call exec_command() to begin the transfer.
 313         </para>
 314         <para>
 315 Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
 316 hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
 317 Command register.
 318         </para>
 319         <para>
 320 Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
 321 hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
 322 command register.
 323         </para>
 324         <para>
 325 Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
 326         </para>
 327
 328         </sect2>
 329
 330         <sect2><title>High-level taskfile hooks</title>
 331         <programlisting>
 332 void (*qc_prep) (struct ata_queued_cmd *qc);
 333 int (*qc_issue) (struct ata_queued_cmd *qc);
 334         </programlisting>
 335
 336         <para>
 337         Higher-level hooks, these two hooks can potentially supercede
 338         several of the above taskfile/DMA engine hooks.  ->qc_prep is
 339         called after the buffers have been DMA-mapped, and is typically
 340         used to populate the hardware's DMA scatter-gather table.
 341         Most drivers use the standard ata_qc_prep() helper function, but
 342         more advanced drivers roll their own.
 343         </para>
 344         <para>
 345         ->qc_issue is used to make a command active, once the hardware
 346         and S/G tables have been prepared.  IDE BMDMA drivers use the
 347         helper function ata_qc_issue_prot() for taskfile protocol-based
 348         dispatch.  More advanced drivers implement their own ->qc_issue.
 349         </para>
 350         <para>
 351         ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
 352         ->bmdma_start() as necessary to initiate a transfer.
 353         </para>
 354
 355         </sect2>
 356
 357         <sect2><title>Timeout (error) handling</title>
 358         <programlisting>
 359 void (*eng_timeout) (struct ata_port *ap);
 360         </programlisting>
 361
 362         <para>
 363 This is a high level error handling function, called from the
 364 error handling thread, when a command times out.  Most newer
 365 hardware will implement its own error handling code here.  IDE BMDMA
 366 drivers may use the helper function ata_eng_timeout().
 367         </para>
 368
 369         </sect2>
 370
 371         <sect2><title>Hardware interrupt handling</title>
 372         <programlisting>
 373 irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
 374 void (*irq_clear) (struct ata_port *);
 375         </programlisting>
 376
 377         <para>
 378         ->irq_handler is the interrupt handling routine registered with
 379         the system, by libata.  ->irq_clear is called during probe just
 380         before the interrupt handler is registered, to be sure hardware
 381         is quiet.
 382         </para>
 383         <para>
 384         The second argument, dev_instance, should be cast to a pointer
 385         to struct ata_host_set.
 386         </para>
 387         <para>
 388         Most legacy IDE drivers use ata_interrupt() for the
 389         irq_handler hook, which scans all ports in the host_set,
 390         determines which queued command was active (if any), and calls
 391         ata_host_intr(ap,qc).
 392         </para>
 393         <para>
 394         Most legacy IDE drivers use ata_bmdma_irq_clear() for the
 395         irq_clear() hook, which simply clears the interrupt and error
 396         flags in the DMA status register.
 397         </para>
 398
 399         </sect2>
 400
 401         <sect2><title>SATA phy read/write</title>
 402         <programlisting>
 403 u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
 404 void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
 405                    u32 val);
 406         </programlisting>
 407
 408         <para>
 409         Read and write standard SATA phy registers.  Currently only used
 410         if ->phy_reset hook called the sata_phy_reset() helper function.
 411         sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
 412         </para>
 413
 414         </sect2>
 415
 416         <sect2><title>Init and shutdown</title>
 417         <programlisting>
 418 int (*port_start) (struct ata_port *ap);
 419 void (*port_stop) (struct ata_port *ap);
 420 void (*host_stop) (struct ata_host_set *host_set);
 421         </programlisting>
 422
 423         <para>
 424         ->port_start() is called just after the data structures for each
 425         port are initialized.  Typically this is used to alloc per-port
 426         DMA buffers / tables / rings, enable DMA engines, and similar
 427         tasks.  Some drivers also use this entry point as a chance to
 428         allocate driver-private memory for ap->private_data.
 429         </para>
 430         <para>
 431         Many drivers use ata_port_start() as this hook or call
 432         it from their own port_start() hooks.  ata_port_start()
 433         allocates space for a legacy IDE PRD table and returns.
 434         </para>
 435         <para>
 436         ->port_stop() is called after ->host_stop().  It's sole function
 437         is to release DMA/memory resources, now that they are no longer
 438         actively being used.  Many drivers also free driver-private
 439         data from port at this time.
 440         </para>
 441         <para>
 442         Many drivers use ata_port_stop() as this hook, which frees the
 443         PRD table.
 444         </para>
 445         <para>
 446         ->host_stop() is called after all ->port_stop() calls
 447 have completed.  The hook must finalize hardware shutdown, release DMA
 448 and other resources, etc.
 449         This hook may be specified as NULL, in which case it is not called.
 450         </para>
 451
 452         </sect2>
 453
 454      </sect1>
 455   </chapter>
 456
 457   <chapter id="libataEH">
 458         <title>Error handling</title>
 459
 460         <para>
 461         This chapter describes how errors are handled under libata.
 462         Readers are advised to read SCSI EH
 463         (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first.
 464         </para>
 465
 466         <sect1><title>Origins of commands</title>
 467         <para>
 468         In libata, a command is represented with struct ata_queued_cmd
 469         or qc.  qc's are preallocated during port initialization and
 470         repetitively used for command executions.  Currently only one
 471         qc is allocated per port but yet-to-be-merged NCQ branch
 472         allocates one for each tag and maps each qc to NCQ tag 1-to-1.
 473         </para>
 474         <para>
 475         libata commands can originate from two sources - libata itself
 476         and SCSI midlayer.  libata internal commands are used for
 477         initialization and error handling.  All normal blk requests
 478         and commands for SCSI emulation are passed as SCSI commands
 479         through queuecommand callback of SCSI host template.
 480         </para>
 481         </sect1>
 482
 483         <sect1><title>How commands are issued</title>
 484
 485         <variablelist>
 486
 487         <varlistentry><term>Internal commands</term>
 488         <listitem>
 489         <para>
 490         First, qc is allocated and initialized using
 491         ata_qc_new_init().  Although ata_qc_new_init() doesn't
 492         implement any wait or retry mechanism when qc is not
 493         available, internal commands are currently issued only during
 494         initialization and error recovery, so no other command is
 495         active and allocation is guaranteed to succeed.
 496         </para>
 497         <para>
 498         Once allocated qc's taskfile is initialized for the command to
 499         be executed.  qc currently has two mechanisms to notify
 500         completion.  One is via qc->complete_fn() callback and the
 501         other is completion qc->waiting.  qc->complete_fn() callback
 502         is the asynchronous path used by normal SCSI translated
 503         commands and qc->waiting is the synchronous (issuer sleeps in
 504         process context) path used by internal commands.
 505         </para>
 506         <para>
 507         Once initialization is complete, host_set lock is acquired
 508         and the qc is issued.
 509         </para>
 510         </listitem>
 511         </varlistentry>
 512
 513         <varlistentry><term>SCSI commands</term>
 514         <listitem>
 515         <para>
 516         All libata drivers use ata_scsi_queuecmd() as
 517         hostt->queuecommand callback.  scmds can either be simulated
 518         or translated.  No qc is involved in processing a simulated
 519         scmd.  The result is computed right away and the scmd is
 520         completed.
 521         </para>
 522         <para>
 523         For a translated scmd, ata_qc_new_init() is invoked to
 524         allocate a qc and the scmd is translated into the qc.  SCSI
 525         midlayer's completion notification function pointer is stored
 526         into qc->scsidone.
 527         </para>
 528         <para>
 529         qc->complete_fn() callback is used for completion
 530         notification.  ATA commands use ata_scsi_qc_complete() while
 531         ATAPI commands use atapi_qc_complete().  Both functions end up
 532         calling qc->scsidone to notify upper layer when the qc is
 533         finished.  After translation is completed, the qc is issued
 534         with ata_qc_issue().
 535         </para>
 536         <para>
 537         Note that SCSI midlayer invokes hostt->queuecommand while
 538         holding host_set lock, so all above occur while holding
 539         host_set lock.
 540         </para>
 541         </listitem>
 542         </varlistentry>
 543
 544         </variablelist>
 545         </sect1>
 546
 547         <sect1><title>How commands are processed</title>
 548         <para>
 549         Depending on which protocol and which controller are used,
 550         commands are processed differently.  For the purpose of
 551         discussion, a controller which uses taskfile interface and all
 552         standard callbacks is assumed.
 553         </para>
 554         <para>
 555         Currently 6 ATA command protocols are used.  They can be
 556         sorted into the following four categories according to how
 557         they are processed.
 558         </para>
 559
 560         <variablelist>
 561            <varlistentry><term>ATA NO DATA or DMA</term>
 562            <listitem>
 563            <para>
 564            ATA_PROT_NODATA and ATA_PROT_DMA fall into this category.
 565            These types of commands don't require any software
 566            intervention once issued.  Device will raise interrupt on
 567            completion.
 568            </para>
 569            </listitem>
 570            </varlistentry>
 571
 572            <varlistentry><term>ATA PIO</term>
 573            <listitem>
 574            <para>
 575            ATA_PROT_PIO is in this category.  libata currently
 576            implements PIO with polling.  ATA_NIEN bit is set to turn
 577            off interrupt and pio_task on ata_wq performs polling and
 578            IO.
 579            </para>
 580            </listitem>
 581            </varlistentry>
 582
 583            <varlistentry><term>ATAPI NODATA or DMA</term>
 584            <listitem>
 585            <para>
 586            ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this
 587            category.  packet_task is used to poll BSY bit after
 588            issuing PACKET command.  Once BSY is turned off by the
 589            device, packet_task transfers CDB and hands off processing
 590            to interrupt handler.
 591            </para>
 592            </listitem>
 593            </varlistentry>
 594
 595            <varlistentry><term>ATAPI PIO</term>
 596            <listitem>
 597            <para>
 598            ATA_PROT_ATAPI is in this category.  ATA_NIEN bit is set
 599            and, as in ATAPI NODATA or DMA, packet_task submits cdb.
 600            However, after submitting cdb, further processing (data
 601            transfer) is handed off to pio_task.
 602            </para>
 603            </listitem>
 604            </varlistentry>
 605         </variablelist>
 606         </sect1>
 607
 608         <sect1><title>How commands are completed</title>
 609         <para>
 610         Once issued, all qc's are either completed with
 611         ata_qc_complete() or time out.  For commands which are handled
 612         by interrupts, ata_host_intr() invokes ata_qc_complete(), and,
 613         for PIO tasks, pio_task invokes ata_qc_complete().  In error
 614         cases, packet_task may also complete commands.
 615         </para>
 616         <para>
 617         ata_qc_complete() does the following.
 618         </para>
 619
 620         <orderedlist>
 621
 622         <listitem>
 623         <para>
 624         DMA memory is unmapped.
 625         </para>
 626         </listitem>
 627
 628         <listitem>
 629         <para>
 630         ATA_QCFLAG_ACTIVE is clared from qc->flags.
 631         </para>
 632         </listitem>
 633
 634         <listitem>
 635         <para>
 636         qc->complete_fn() callback is invoked.  If the return value of
 637         the callback is not zero.  Completion is short circuited and
 638         ata_qc_complete() returns.
 639         </para>
 640         </listitem>
 641
 642         <listitem>
 643         <para>
 644         __ata_qc_complete() is called, which does
 645            <orderedlist>
 646
 647            <listitem>
 648            <para>
 649            qc->flags is cleared to zero.
 650            </para>
 651            </listitem>
 652
 653            <listitem>
 654            <para>
 655            ap->active_tag and qc->tag are poisoned.
 656            </para>
 657            </listitem>
 658
 659            <listitem>
 660            <para>
 661            qc->waiting is claread &amp; completed (in that order).
 662            </para>
 663            </listitem>
 664
 665            <listitem>
 666            <para>
 667            qc is deallocated by clearing appropriate bit in ap->qactive.
 668            </para>
 669            </listitem>
 670
 671            </orderedlist>
 672         </para>
 673         </listitem>
 674
 675         </orderedlist>
 676
 677         <para>
 678         So, it basically notifies upper layer and deallocates qc.  One
 679         exception is short-circuit path in #3 which is used by
 680         atapi_qc_complete().
 681         </para>
 682         <para>
 683         For all non-ATAPI commands, whether it fails or not, almost
 684         the same code path is taken and very little error handling
 685         takes place.  A qc is completed with success status if it
 686         succeeded, with failed status otherwise.
 687         </para>
 688         <para>
 689         However, failed ATAPI commands require more handling as
 690         REQUEST SENSE is needed to acquire sense data.  If an ATAPI
 691         command fails, ata_qc_complete() is invoked with error status,
 692         which in turn invokes atapi_qc_complete() via
 693         qc->complete_fn() callback.
 694         </para>
 695         <para>
 696         This makes atapi_qc_complete() set scmd->result to
 697         SAM_STAT_CHECK_CONDITION, complete the scmd and return 1.  As
 698         the sense data is empty but scmd->result is CHECK CONDITION,
 699         SCSI midlayer will invoke EH for the scmd, and returning 1
 700         makes ata_qc_complete() to return without deallocating the qc.
 701         This leads us to ata_scsi_error() with partially completed qc.
 702         </para>
 703
 704         </sect1>
 705
 706         <sect1><title>ata_scsi_error()</title>
 707         <para>
 708         ata_scsi_error() is the current transportt->eh_strategy_handler()
 709         for libata.  As discussed above, this will be entered in two
 710         cases - timeout and ATAPI error completion.  This function
 711         calls low level libata driver's eng_timeout() callback, the
 712         standard callback for which is ata_eng_timeout().  It checks
 713         if a qc is active and calls ata_qc_timeout() on the qc if so.
 714         Actual error handling occurs in ata_qc_timeout().
 715         </para>
 716         <para>
 717         If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and
 718         completes the qc.  Note that as we're currently in EH, we
 719         cannot call scsi_done.  As described in SCSI EH doc, a
 720         recovered scmd should be either retried with
 721         scsi_queue_insert() or finished with scsi_finish_command().
 722         Here, we override qc->scsidone with scsi_finish_command() and
 723         calls ata_qc_complete().
 724         </para>
 725         <para>
 726         If EH is invoked due to a failed ATAPI qc, the qc here is
 727         completed but not deallocated.  The purpose of this
 728         half-completion is to use the qc as place holder to make EH
 729         code reach this place.  This is a bit hackish, but it works.
 730         </para>
 731         <para>
 732         Once control reaches here, the qc is deallocated by invoking
 733         __ata_qc_complete() explicitly.  Then, internal qc for REQUEST
 734         SENSE is issued.  Once sense data is acquired, scmd is
 735         finished by directly invoking scsi_finish_command() on the
 736         scmd.  Note that as we already have completed and deallocated
 737         the qc which was associated with the scmd, we don't need
 738         to/cannot call ata_qc_complete() again.
 739         </para>
 740
 741         </sect1>
 742
 743         <sect1><title>Problems with the current EH</title>
 744
 745         <itemizedlist>
 746
 747         <listitem>
 748         <para>
 749         Error representation is too crude.  Currently any and all
 750         error conditions are represented with ATA STATUS and ERROR
 751         registers.  Errors which aren't ATA device errors are treated
 752         as ATA device errors by setting ATA_ERR bit.  Better error
 753         descriptor which can properly represent ATA and other
 754         errors/exceptions is needed.
 755         </para>
 756         </listitem>
 757
 758         <listitem>
 759         <para>
 760         When handling timeouts, no action is taken to make device
 761         forget about the timed out command and ready for new commands.
 762         </para>
 763         </listitem>
 764
 765         <listitem>
 766         <para>
 767         EH handling via ata_scsi_error() is not properly protected
 768         from usual command processing.  On EH entrance, the device is
 769         not in quiescent state.  Timed out commands may succeed or
 770         fail any time.  pio_task and atapi_task may still be running.
 771         </para>
 772         </listitem>
 773
 774         <listitem>
 775         <para>
 776         Too weak error recovery.  Devices / controllers causing HSM
 777         mismatch errors and other errors quite often require reset to
 778         return to known state.  Also, advanced error handling is
 779         necessary to support features like NCQ and hotplug.
 780         </para>
 781         </listitem>
 782
 783         <listitem>
 784         <para>
 785         ATA errors are directly handled in the interrupt handler and
 786         PIO errors in pio_task.  This is problematic for advanced
 787         error handling for the following reasons.
 788         </para>
 789         <para>
 790         First, advanced error handling often requires context and
 791         internal qc execution.
 792         </para>
 793         <para>
 794         Second, even a simple failure (say, CRC error) needs
 795         information gathering and could trigger complex error handling
 796         (say, resetting &amp; reconfiguring).  Having multiple code
 797         paths to gather information, enter EH and trigger actions
 798         makes life painful.
 799         </para>
 800         <para>
 801         Third, scattered EH code makes implementing low level drivers
 802         difficult.  Low level drivers override libata callbacks.  If
 803         EH is scattered over several places, each affected callbacks
 804         should perform its part of error handling.  This can be error
 805         prone and painful.
 806         </para>
 807         </listitem>
 808
 809         </itemizedlist>
 810         </sect1>
 811   </chapter>
 812
 813   <chapter id="libataExt">
 814      <title>libata Library</title>
 815 !Edrivers/scsi/libata-core.c
 816   </chapter>
 817
 818   <chapter id="libataInt">
 819      <title>libata Core Internals</title>
 820 !Idrivers/scsi/libata-core.c
 821   </chapter>
 822
 823   <chapter id="libataScsiInt">
 824      <title>libata SCSI translation/emulation</title>
 825 !Edrivers/scsi/libata-scsi.c
 826 !Idrivers/scsi/libata-scsi.c
 827   </chapter>
 828
 829   <chapter id="ataExceptions">
 830      <title>ATA errors &amp; exceptions</title>
 831
 832   <para>
 833   This chapter tries to identify what error/exception conditions exist
 834   for ATA/ATAPI devices and describe how they should be handled in
 835   implementation-neutral way.
 836   </para>
 837
 838   <para>
 839   The term 'error' is used to describe conditions where either an
 840   explicit error condition is reported from device or a command has
 841   timed out.
 842   </para>
 843
 844   <para>
 845   The term 'exception' is either used to describe exceptional
 846   conditions which are not errors (say, power or hotplug events), or
 847   to describe both errors and non-error exceptional conditions.  Where
 848   explicit distinction between error and exception is necessary, the
 849   term 'non-error exception' is used.
 850   </para>
 851
 852   <sect1 id="excat">
 853      <title>Exception categories</title>
 854      <para>
 855      Exceptions are described primarily with respect to legacy
 856      taskfile + bus master IDE interface.  If a controller provides
 857      other better mechanism for error reporting, mapping those into
 858      categories described below shouldn't be difficult.
 859      </para>
 860
 861      <para>
 862      In the following sections, two recovery actions - reset and
 863      reconfiguring transport - are mentioned.  These are described
 864      further in <xref linkend="exrec"/>.
 865      </para>
 866
 867      <sect2 id="excatHSMviolation">
 868         <title>HSM violation</title>
 869         <para>
 870         This error is indicated when STATUS value doesn't match HSM
 871         requirement during issuing or excution any ATA/ATAPI command.
 872         </para>
 873
 874         <itemizedlist>
 875         <title>Examples</title>
 876
 877         <listitem>
 878         <para>
 879         ATA_STATUS doesn't contain !BSY &amp;&amp; DRDY &amp;&amp; !DRQ while trying
 880         to issue a command.
 881         </para>
 882         </listitem>
 883
 884         <listitem>
 885         <para>
 886         !BSY &amp;&amp; !DRQ during PIO data transfer.
 887         </para>
 888         </listitem>
 889
 890         <listitem>
 891         <para>
 892         DRQ on command completion.
 893         </para>
 894         </listitem>
 895
 896         <listitem>
 897         <para>
 898         !BSY &amp;&amp; ERR after CDB tranfer starts but before the
 899         last byte of CDB is transferred.  ATA/ATAPI standard states
 900         that &quot;The device shall not terminate the PACKET command
 901         with an error before the last byte of the command packet has
 902         been written&quot; in the error outputs description of PACKET
 903         command and the state diagram doesn't include such
 904         transitions.
 905         </para>
 906         </listitem>
 907
 908         </itemizedlist>
 909
 910         <para>
 911         In these cases, HSM is violated and not much information
 912         regarding the error can be acquired from STATUS or ERROR
 913         register.  IOW, this error can be anything - driver bug,
 914         faulty device, controller and/or cable.
 915         </para>
 916
 917         <para>
 918         As HSM is violated, reset is necessary to restore known state.
 919         Reconfiguring transport for lower speed might be helpful too
 920         as transmission errors sometimes cause this kind of errors.
 921         </para>
 922      </sect2>
 923
 924      <sect2 id="excatDevErr">
 925         <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title>
 926
 927         <para>
 928         These are errors detected and reported by ATA/ATAPI devices
 929         indicating device problems.  For this type of errors, STATUS
 930         and ERROR register values are valid and describe error
 931         condition.  Note that some of ATA bus errors are detected by
 932         ATA/ATAPI devices and reported using the same mechanism as
 933         device errors.  Those cases are described later in this
 934         section.
 935         </para>
 936
 937         <para>
 938         For ATA commands, this type of errors are indicated by !BSY
 939         &amp;&amp; ERR during command execution and on completion.
 940         </para>
 941
 942         <para>For ATAPI commands,</para>
 943
 944         <itemizedlist>
 945
 946         <listitem>
 947         <para>
 948         !BSY &amp;&amp; ERR &amp;&amp; ABRT right after issuing PACKET
 949         indicates that PACKET command is not supported and falls in
 950         this category.
 951         </para>
 952         </listitem>
 953
 954         <listitem>
 955         <para>
 956         !BSY &amp;&amp; ERR(==CHK) &amp;&amp; !ABRT after the last
 957         byte of CDB is transferred indicates CHECK CONDITION and
 958         doesn't fall in this category.
 959         </para>
 960         </listitem>
 961
 962         <listitem>
 963         <para>
 964         !BSY &amp;&amp; ERR(==CHK) &amp;&amp; ABRT after the last byte
 965         of CDB is transferred *probably* indicates CHECK CONDITION and
 966         doesn't fall in this category.
 967         </para>
 968         </listitem>
 969
 970         </itemizedlist>
 971
 972         <para>
 973         Of errors detected as above, the followings are not ATA/ATAPI
 974         device errors but ATA bus errors and should be handled
 975         according to <xref linkend="excatATAbusErr"/>.
 976         </para>
 977
 978         <variablelist>
 979
 980            <varlistentry>
 981            <term>CRC error during data transfer</term>
 982            <listitem>
 983            <para>
 984            This is indicated by ICRC bit in the ERROR register and
 985            means that corruption occurred during data transfer.  Upto
 986            ATA/ATAPI-7, the standard specifies that this bit is only
 987            applicable to UDMA transfers but ATA/ATAPI-8 draft revision
 988            1f says that the bit may be applicable to multiword DMA and
 989            PIO.
 990            </para>
 991            </listitem>
 992            </varlistentry>
 993
 994            <varlistentry>
 995            <term>ABRT error during data transfer or on completion</term>
 996            <listitem>
 997            <para>
 998            Upto ATA/ATAPI-7, the standard specifies that ABRT could be
 999            set on ICRC errors and on cases where a device is not able
1000            to complete a command.  Combined with the fact that MWDMA
1001            and PIO transfer errors aren't allowed to use ICRC bit upto
1002            ATA/ATAPI-7, it seems to imply that ABRT bit alone could
1003            indicate tranfer errors.
1004            </para>
1005            <para>
1006            However, ATA/ATAPI-8 draft revision 1f removes the part
1007            that ICRC errors can turn on ABRT.  So, this is kind of
1008            gray area.  Some heuristics are needed here.
1009            </para>
1010            </listitem>
1011            </varlistentry>
1012
1013         </variablelist>
1014
1015         <para>
1016         ATA/ATAPI device errors can be further categorized as follows.
1017         </para>
1018
1019         <variablelist>
1020
1021            <varlistentry>
1022            <term>Media errors</term>
1023            <listitem>
1024            <para>
1025            This is indicated by UNC bit in the ERROR register.  ATA
1026            devices reports UNC error only after certain number of
1027            retries cannot recover the data, so there's nothing much
1028            else to do other than notifying upper layer.
1029            </para>
1030            <para>
1031            READ and WRITE commands report CHS or LBA of the first
1032            failed sector but ATA/ATAPI standard specifies that the
1033            amount of transferred data on error completion is
1034            indeterminate, so we cannot assume that sectors preceding
1035            the failed sector have been transferred and thus cannot
1036            complete those sectors successfully as SCSI does.
1037            </para>
1038            </listitem>
1039            </varlistentry>
1040
1041            <varlistentry>
1042            <term>Media changed / media change requested error</term>
1043            <listitem>
1044            <para>
1045            &lt;&lt;TODO: fill here&gt;&gt;
1046            </para>
1047            </listitem>
1048            </varlistentry>
1049
1050            <varlistentry><term>Address error</term>
1051            <listitem>
1052            <para>
1053            This is indicated by IDNF bit in the ERROR register.
1054            Report to upper layer.
1055            </para>
1056            </listitem>
1057            </varlistentry>
1058
1059            <varlistentry><term>Other errors</term>
1060            <listitem>
1061            <para>
1062            This can be invalid command or parameter indicated by ABRT
1063            ERROR bit or some other error condition.  Note that ABRT
1064            bit can indicate a lot of things including ICRC and Address
1065            errors.  Heuristics needed.
1066            </para>
1067            </listitem>
1068            </varlistentry>
1069
1070         </variablelist>
1071
1072         <para>
1073         Depending on commands, not all STATUS/ERROR bits are
1074         applicable.  These non-applicable bits are marked with
1075         &quot;na&quot; in the output descriptions but upto ATA/ATAPI-7
1076         no definition of &quot;na&quot; can be found.  However,
1077         ATA/ATAPI-8 draft revision 1f describes &quot;N/A&quot; as
1078         follows.
1079         </para>
1080
1081         <blockquote>
1082         <variablelist>
1083            <varlistentry><term>3.2.3.3a N/A</term>
1084            <listitem>
1085            <para>
1086            A keyword the indicates a field has no defined value in
1087            this standard and should not be checked by the host or
1088            device. N/A fields should be cleared to zero.
1089            </para>
1090            </listitem>
1091            </varlistentry>
1092         </variablelist>
1093         </blockquote>
1094
1095         <para>
1096         So, it seems reasonable to assume that &quot;na&quot; bits are
1097         cleared to zero by devices and thus need no explicit masking.
1098         </para>
1099
1100      </sect2>
1101
1102      <sect2 id="excatATAPIcc">
1103         <title>ATAPI device CHECK CONDITION</title>
1104
1105         <para>
1106         ATAPI device CHECK CONDITION error is indicated by set CHK bit
1107         (ERR bit) in the STATUS register after the last byte of CDB is
1108         transferred for a PACKET command.  For this kind of errors,
1109         sense data should be acquired to gather information regarding
1110         the errors.  REQUEST SENSE packet command should be used to
1111         acquire sense data.
1112         </para>
1113
1114         <para>
1115         Once sense data is acquired, this type of errors can be
1116         handled similary to other SCSI errors.  Note that sense data
1117         may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR
1118         &amp;&amp; ASC/ASCQ 47h/00h SCSI PARITY ERROR).  In such
1119         cases, the error should be considered as an ATA bus error and
1120         handled according to <xref linkend="excatATAbusErr"/>.
1121         </para>
1122
1123      </sect2>
1124
1125      <sect2 id="excatNCQerr">
1126         <title>ATA device error (NCQ)</title>
1127
1128         <para>
1129         NCQ command error is indicated by cleared BSY and set ERR bit
1130         during NCQ command phase (one or more NCQ commands
1131         outstanding).  Although STATUS and ERROR registers will
1132         contain valid values describing the error, READ LOG EXT is
1133         required to clear the error condition, determine which command
1134         has failed and acquire more information.
1135         </para>
1136
1137         <para>
1138         READ LOG EXT Log Page 10h reports which tag has failed and
1139         taskfile register values describing the error.  With this
1140         information the failed command can be handled as a normal ATA
1141         command error as in <xref linkend="excatDevErr"/> and all
1142         other in-flight commands must be retried.  Note that this
1143         retry should not be counted - it's likely that commands
1144         retried this way would have completed normally if it were not
1145         for the failed command.
1146         </para>
1147
1148         <para>
1149         Note that ATA bus errors can be reported as ATA device NCQ
1150         errors.  This should be handled as described in <xref
1151         linkend="excatATAbusErr"/>.
1152         </para>
1153
1154         <para>
1155         If READ LOG EXT Log Page 10h fails or reports NQ, we're
1156         thoroughly screwed.  This condition should be treated
1157         according to <xref linkend="excatHSMviolation"/>.
1158         </para>
1159
1160      </sect2>
1161
1162      <sect2 id="excatATAbusErr">
1163         <title>ATA bus error</title>
1164
1165         <para>
1166         ATA bus error means that data corruption occurred during
1167         transmission over ATA bus (SATA or PATA).  This type of errors
1168         can be indicated by
1169         </para>
1170
1171         <itemizedlist>
1172
1173         <listitem>
1174         <para>
1175         ICRC or ABRT error as described in <xref linkend="excatDevErr"/>.
1176         </para>
1177         </listitem>
1178
1179         <listitem>
1180         <para>
1181         Controller-specific error completion with error information
1182         indicating transmission error.
1183         </para>
1184         </listitem>
1185
1186         <listitem>
1187         <para>
1188         On some controllers, command timeout.  In this case, there may
1189         be a mechanism to determine that the timeout is due to
1190         transmission error.
1191         </para>
1192         </listitem>
1193
1194         <listitem>
1195         <para>
1196         Unknown/random errors, timeouts and all sorts of weirdities.
1197         </para>
1198         </listitem>
1199
1200         </itemizedlist>
1201
1202         <para>
1203         As described above, transmission errors can cause wide variety
1204         of symptoms ranging from device ICRC error to random device
1205         lockup, and, for many cases, there is no way to tell if an
1206         error condition is due to transmission error or not;
1207         therefore, it's necessary to employ some kind of heuristic
1208         when dealing with errors and timeouts.  For example,
1209         encountering repetitive ABRT errors for known supported
1210         command is likely to indicate ATA bus error.
1211         </para>
1212
1213         <para>
1214         Once it's determined that ATA bus errors have possibly
1215         occurred, lowering ATA bus transmission speed is one of
1216         actions which may alleviate the problem.  See <xref
1217         linkend="exrecReconf"/> for more information.
1218         </para>
1219
1220      </sect2>
1221
1222      <sect2 id="excatPCIbusErr">
1223         <title>PCI bus error</title>
1224
1225         <para>
1226         Data corruption or other failures during transmission over PCI
1227         (or other system bus).  For standard BMDMA, this is indicated
1228         by Error bit in the BMDMA Status register.  This type of
1229         errors must be logged as it indicates something is very wrong
1230         with the system.  Resetting host controller is recommended.
1231         </para>
1232
1233      </sect2>
1234
1235      <sect2 id="excatLateCompletion">
1236         <title>Late completion</title>
1237
1238         <para>
1239         This occurs when timeout occurs and the timeout handler finds
1240         out that the timed out command has completed successfully or
1241         with error.  This is usually caused by lost interrupts.  This
1242         type of errors must be logged.  Resetting host controller is
1243         recommended.
1244         </para>
1245
1246      </sect2>
1247
1248      <sect2 id="excatUnknown">
1249         <title>Unknown error (timeout)</title>
1250
1251         <para>
1252         This is when timeout occurs and the command is still
1253         processing or the host and device are in unknown state.  When
1254         this occurs, HSM could be in any valid or invalid state.  To
1255         bring the device to known state and make it forget about the
1256         timed out command, resetting is necessary.  The timed out
1257         command may be retried.
1258         </para>
1259
1260         <para>
1261         Timeouts can also be caused by transmission errors.  Refer to
1262         <xref linkend="excatATAbusErr"/> for more details.
1263         </para>
1264
1265      </sect2>
1266
1267      <sect2 id="excatHoplugPM">
1268         <title>Hotplug and power management exceptions</title>
1269
1270         <para>
1271         &lt;&lt;TODO: fill here&gt;&gt;
1272         </para>
1273
1274      </sect2>
1275
1276   </sect1>
1277
1278   <sect1 id="exrec">
1279      <title>EH recovery actions</title>
1280
1281      <para>
1282      This section discusses several important recovery actions.
1283      </para>
1284
1285      <sect2 id="exrecClr">
1286         <title>Clearing error condition</title>
1287
1288         <para>
1289         Many controllers require its error registers to be cleared by
1290         error handler.  Different controllers may have different
1291         requirements.
1292         </para>
1293
1294         <para>
1295         For SATA, it's strongly recommended to clear at least SError
1296         register during error handling.
1297         </para>
1298      </sect2>
1299
1300      <sect2 id="exrecRst">
1301         <title>Reset</title>
1302
1303         <para>
1304         During EH, resetting is necessary in the following cases.
1305         </para>
1306
1307         <itemizedlist>
1308
1309         <listitem>
1310         <para>
1311         HSM is in unknown or invalid state
1312         </para>
1313         </listitem>
1314
1315         <listitem>
1316         <para>
1317         HBA is in unknown or invalid state
1318         </para>
1319         </listitem>
1320
1321         <listitem>
1322         <para>
1323         EH needs to make HBA/device forget about in-flight commands
1324         </para>
1325         </listitem>
1326
1327         <listitem>
1328         <para>
1329         HBA/device behaves weirdly
1330         </para>
1331         </listitem>
1332
1333         </itemizedlist>
1334
1335         <para>
1336         Resetting during EH might be a good idea regardless of error
1337         condition to improve EH robustness.  Whether to reset both or
1338         either one of HBA and device depends on situation but the
1339         following scheme is recommended.
1340         </para>
1341
1342         <itemizedlist>
1343
1344         <listitem>
1345         <para>
1346         When it's known that HBA is in ready state but ATA/ATAPI
1347         device in in unknown state, reset only device.
1348         </para>
1349         </listitem>
1350
1351         <listitem>
1352         <para>
1353         If HBA is in unknown state, reset both HBA and device.
1354         </para>
1355         </listitem>
1356
1357         </itemizedlist>
1358
1359         <para>
1360         HBA resetting is implementation specific.  For a controller
1361         complying to taskfile/BMDMA PCI IDE, stopping active DMA
1362         transaction may be sufficient iff BMDMA state is the only HBA
1363         context.  But even mostly taskfile/BMDMA PCI IDE complying
1364         controllers may have implementation specific requirements and
1365         mechanism to reset themselves.  This must be addressed by
1366         specific drivers.
1367         </para>
1368
1369         <para>
1370         OTOH, ATA/ATAPI standard describes in detail ways to reset
1371         ATA/ATAPI devices.
1372         </para>
1373
1374         <variablelist>
1375
1376            <varlistentry><term>PATA hardware reset</term>
1377            <listitem>
1378            <para>
1379            This is hardware initiated device reset signalled with
1380            asserted PATA RESET- signal.  There is no standard way to
1381            initiate hardware reset from software although some
1382            hardware provides registers that allow driver to directly
1383            tweak the RESET- signal.
1384            </para>
1385            </listitem>
1386            </varlistentry>
1387
1388            <varlistentry><term>Software reset</term>
1389            <listitem>
1390            <para>
1391            This is achieved by turning CONTROL SRST bit on for at
1392            least 5us.  Both PATA and SATA support it but, in case of
1393            SATA, this may require controller-specific support as the
1394            second Register FIS to clear SRST should be transmitted
1395            while BSY bit is still set.  Note that on PATA, this resets
1396            both master and slave devices on a channel.
1397            </para>
1398            </listitem>
1399            </varlistentry>
1400
1401            <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term>
1402            <listitem>
1403            <para>
1404            Although ATA/ATAPI standard doesn't describe exactly, EDD
1405            implies some level of resetting, possibly similar level
1406            with software reset.  Host-side EDD protocol can be handled
1407            with normal command processing and most SATA controllers
1408            should be able to handle EDD's just like other commands.
1409            As in software reset, EDD affects both devices on a PATA
1410            bus.
1411            </para>
1412            <para>
1413            Although EDD does reset devices, this doesn't suit error
1414            handling as EDD cannot be issued while BSY is set and it's
1415            unclear how it will act when device is in unknown/weird
1416            state.
1417            </para>
1418            </listitem>
1419            </varlistentry>
1420
1421            <varlistentry><term>ATAPI DEVICE RESET command</term>
1422            <listitem>
1423            <para>
1424            This is very similar to software reset except that reset
1425            can be restricted to the selected device without affecting
1426            the other device sharing the cable.
1427            </para>
1428            </listitem>
1429            </varlistentry>
1430
1431            <varlistentry><term>SATA phy reset</term>
1432            <listitem>
1433            <para>
1434            This is the preferred way of resetting a SATA device.  In
1435            effect, it's identical to PATA hardware reset.  Note that
1436            this can be done with the standard SCR Control register.
1437            As such, it's usually easier to implement than software
1438            reset.
1439            </para>
1440            </listitem>
1441            </varlistentry>
1442
1443         </variablelist>
1444
1445         <para>
1446         One more thing to consider when resetting devices is that
1447         resetting clears certain configuration parameters and they
1448         need to be set to their previous or newly adjusted values
1449         after reset.
1450         </para>
1451
1452         <para>
1453         Parameters affected are.
1454         </para>
1455
1456         <itemizedlist>
1457
1458         <listitem>
1459         <para>
1460         CHS set up with INITIALIZE DEVICE PARAMETERS (seldomly used)
1461         </para>
1462         </listitem>
1463
1464         <listitem>
1465         <para>
1466         Parameters set with SET FEATURES including transfer mode setting
1467         </para>
1468         </listitem>
1469
1470         <listitem>
1471         <para>
1472         Block count set with SET MULTIPLE MODE
1473         </para>
1474         </listitem>
1475
1476         <listitem>
1477         <para>
1478         Other parameters (SET MAX, MEDIA LOCK...)
1479         </para>
1480         </listitem>
1481
1482         </itemizedlist>
1483
1484         <para>
1485         ATA/ATAPI standard specifies that some parameters must be
1486         maintained across hardware or software reset, but doesn't
1487         strictly specify all of them.  Always reconfiguring needed
1488         parameters after reset is required for robustness.  Note that
1489         this also applies when resuming from deep sleep (power-off).
1490         </para>
1491
1492         <para>
1493         Also, ATA/ATAPI standard requires that IDENTIFY DEVICE /
1494         IDENTIFY PACKET DEVICE is issued after any configuration
1495         parameter is updated or a hardware reset and the result used
1496         for further operation.  OS driver is required to implement
1497         revalidation mechanism to support this.
1498         </para>
1499
1500      </sect2>
1501
1502      <sect2 id="exrecReconf">
1503         <title>Reconfigure transport</title>
1504
1505         <para>
1506         For both PATA and SATA, a lot of corners are cut for cheap
1507         connectors, cables or controllers and it's quite common to see
1508         high transmission error rate.  This can be mitigated by
1509         lowering transmission speed.
1510         </para>
1511
1512         <para>
1513         The following is a possible scheme Jeff Garzik suggested.
1514         </para>
1515
1516         <blockquote>
1517         <para>
1518         If more than $N (3?) transmission errors happen in 15 minutes,
1519         </para>
1520         <itemizedlist>
1521         <listitem>
1522         <para>
1523         if SATA, decrease SATA PHY speed.  if speed cannot be decreased,
1524         </para>
1525         </listitem>
1526         <listitem>
1527         <para>
1528         decrease UDMA xfer speed.  if at UDMA0, switch to PIO4,
1529         </para>
1530         </listitem>
1531         <listitem>
1532         <para>
1533         decrease PIO xfer speed.  if at PIO3, complain, but continue
1534         </para>
1535         </listitem>
1536         </itemizedlist>
1537         </blockquote>
1538
1539      </sect2>
1540
1541   </sect1>
1542
1543   </chapter>
1544
1545   <chapter id="PiixInt">
1546      <title>ata_piix Internals</title>
1547 !Idrivers/scsi/ata_piix.c
1548   </chapter>
1549
1550   <chapter id="SILInt">
1551      <title>sata_sil Internals</title>
1552 !Idrivers/scsi/sata_sil.c
1553   </chapter>
1554
1555   <chapter id="libataThanks">
1556      <title>Thanks</title>
1557   <para>
1558   The bulk of the ATA knowledge comes thanks to long conversations with
1559   Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
1560   and SCSI specifications.
1561   </para>
1562   <para>
1563   Thanks to Alan Cox for pointing out similarities
1564   between SATA and SCSI, and in general for motivation to hack on
1565   libata.
1566   </para>
1567   <para>
1568   libata's device detection
1569   method, ata_pio_devchk, and in general all the early probing was
1570   based on extensive study of Hale Landis's probe/reset code in his
1571   ATADRVR driver (www.ata-atapi.com).
1572   </para>
1573   </chapter>
1574
1575 </book>