Documentation/DocBook/libata.tmpl

   1 <?xml version="1.0" encoding="UTF-8"?>
   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 *ap);
 124         </programlisting>
 125
 126         <para>
 127         Hooks called prior to the issue of SET FEATURES - XFER MODE
 128         command.  dev->pio_mode is guaranteed to be valid when
 129         ->set_piomode() is called, and dev->dma_mode is guaranteed to be
 130         valid when ->set_dmamode() is called.  ->post_set_mode() is
 131         called unconditionally, after the SET FEATURES - XFER MODE
 132         command completes successfully.
 133         </para>
 134
 135         <para>
 136         ->set_piomode() is always called (if present), but
 137         ->set_dma_mode() is only called if DMA is possible.
 138         </para>
 139
 140         </sect2>
 141
 142         <sect2><title>Taskfile read/write</title>
 143         <programlisting>
 144 void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
 145 void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
 146         </programlisting>
 147
 148         <para>
 149         ->tf_load() is called to load the given taskfile into hardware
 150         registers / DMA buffers.  ->tf_read() is called to read the
 151         hardware registers / DMA buffers, to obtain the current set of
 152         taskfile register values.
 153         Most drivers for taskfile-based hardware (PIO or MMIO) use
 154         ata_tf_load() and ata_tf_read() for these hooks.
 155         </para>
 156
 157         </sect2>
 158
 159         <sect2><title>ATA command execute</title>
 160         <programlisting>
 161 void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
 162         </programlisting>
 163
 164         <para>
 165         causes an ATA command, previously loaded with
 166         ->tf_load(), to be initiated in hardware.
 167         Most drivers for taskfile-based hardware use ata_exec_command()
 168         for this hook.
 169         </para>
 170
 171         </sect2>
 172
 173         <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
 174         <programlisting>
 175 int (*check_atapi_dma) (struct ata_queued_cmd *qc);
 176         </programlisting>
 177
 178         <para>
 179 Allow low-level driver to filter ATA PACKET commands, returning a status
 180 indicating whether or not it is OK to use DMA for the supplied PACKET
 181 command.
 182         </para>
 183         <para>
 184         This hook may be specified as NULL, in which case libata will
 185         assume that atapi dma can be supported.
 186         </para>
 187
 188         </sect2>
 189
 190         <sect2><title>Read specific ATA shadow registers</title>
 191         <programlisting>
 192 u8   (*check_status)(struct ata_port *ap);
 193 u8   (*check_altstatus)(struct ata_port *ap);
 194 u8   (*check_err)(struct ata_port *ap);
 195         </programlisting>
 196
 197         <para>
 198         Reads the Status/AltStatus/Error ATA shadow register from
 199         hardware.  On some hardware, reading the Status register has
 200         the side effect of clearing the interrupt condition.
 201         Most drivers for taskfile-based hardware use
 202         ata_check_status() for this hook.
 203         </para>
 204         <para>
 205         Note that because this is called from ata_device_add(), at
 206         least a dummy function that clears device interrupts must be
 207         provided for all drivers, even if the controller doesn't
 208         actually have a taskfile status register.
 209         </para>
 210
 211         </sect2>
 212
 213         <sect2><title>Select ATA device on bus</title>
 214         <programlisting>
 215 void (*dev_select)(struct ata_port *ap, unsigned int device);
 216         </programlisting>
 217
 218         <para>
 219         Issues the low-level hardware command(s) that causes one of N
 220         hardware devices to be considered 'selected' (active and
 221         available for use) on the ATA bus.  This generally has no
 222         meaning on FIS-based devices.
 223         </para>
 224         <para>
 225         Most drivers for taskfile-based hardware use
 226         ata_std_dev_select() for this hook.  Controllers which do not
 227         support second drives on a port (such as SATA contollers) will
 228         use ata_noop_dev_select().
 229         </para>
 230
 231         </sect2>
 232
 233         <sect2><title>Reset ATA bus</title>
 234         <programlisting>
 235 void (*phy_reset) (struct ata_port *ap);
 236         </programlisting>
 237
 238         <para>
 239         The very first step in the probe phase.  Actions vary depending
 240         on the bus type, typically.  After waking up the device and probing
 241         for device presence (PATA and SATA), typically a soft reset
 242         (SRST) will be performed.  Drivers typically use the helper
 243         functions ata_bus_reset() or sata_phy_reset() for this hook.
 244         Many SATA drivers use sata_phy_reset() or call it from within
 245         their own phy_reset() functions.
 246         </para>
 247
 248         </sect2>
 249
 250         <sect2><title>Control PCI IDE BMDMA engine</title>
 251         <programlisting>
 252 void (*bmdma_setup) (struct ata_queued_cmd *qc);
 253 void (*bmdma_start) (struct ata_queued_cmd *qc);
 254 void (*bmdma_stop) (struct ata_port *ap);
 255 u8   (*bmdma_status) (struct ata_port *ap);
 256         </programlisting>
 257
 258         <para>
 259 When setting up an IDE BMDMA transaction, these hooks arm
 260 (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
 261 the hardware's DMA engine.  ->bmdma_status is used to read the standard
 262 PCI IDE DMA Status register.
 263         </para>
 264
 265         <para>
 266 These hooks are typically either no-ops, or simply not implemented, in
 267 FIS-based drivers.
 268         </para>
 269         <para>
 270 Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
 271 hook.  ata_bmdma_setup() will write the pointer to the PRD table to
 272 the IDE PRD Table Address register, enable DMA in the DMA Command
 273 register, and call exec_command() to begin the transfer.
 274         </para>
 275         <para>
 276 Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
 277 hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
 278 Command register.
 279         </para>
 280         <para>
 281 Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
 282 hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
 283 command register.
 284         </para>
 285         <para>
 286 Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
 287         </para>
 288
 289         </sect2>
 290
 291         <sect2><title>High-level taskfile hooks</title>
 292         <programlisting>
 293 void (*qc_prep) (struct ata_queued_cmd *qc);
 294 int (*qc_issue) (struct ata_queued_cmd *qc);
 295         </programlisting>
 296
 297         <para>
 298         Higher-level hooks, these two hooks can potentially supercede
 299         several of the above taskfile/DMA engine hooks.  ->qc_prep is
 300         called after the buffers have been DMA-mapped, and is typically
 301         used to populate the hardware's DMA scatter-gather table.
 302         Most drivers use the standard ata_qc_prep() helper function, but
 303         more advanced drivers roll their own.
 304         </para>
 305         <para>
 306         ->qc_issue is used to make a command active, once the hardware
 307         and S/G tables have been prepared.  IDE BMDMA drivers use the
 308         helper function ata_qc_issue_prot() for taskfile protocol-based
 309         dispatch.  More advanced drivers implement their own ->qc_issue.
 310         </para>
 311         <para>
 312         ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
 313         ->bmdma_start() as necessary to initiate a transfer.
 314         </para>
 315
 316         </sect2>
 317
 318         <sect2><title>Timeout (error) handling</title>
 319         <programlisting>
 320 void (*eng_timeout) (struct ata_port *ap);
 321         </programlisting>
 322
 323         <para>
 324 This is a high level error handling function, called from the
 325 error handling thread, when a command times out.  Most newer
 326 hardware will implement its own error handling code here.  IDE BMDMA
 327 drivers may use the helper function ata_eng_timeout().
 328         </para>
 329
 330         </sect2>
 331
 332         <sect2><title>Hardware interrupt handling</title>
 333         <programlisting>
 334 irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
 335 void (*irq_clear) (struct ata_port *);
 336         </programlisting>
 337
 338         <para>
 339         ->irq_handler is the interrupt handling routine registered with
 340         the system, by libata.  ->irq_clear is called during probe just
 341         before the interrupt handler is registered, to be sure hardware
 342         is quiet.
 343         </para>
 344         <para>
 345         The second argument, dev_instance, should be cast to a pointer
 346         to struct ata_host_set.
 347         </para>
 348         <para>
 349         Most legacy IDE drivers use ata_interrupt() for the
 350         irq_handler hook, which scans all ports in the host_set,
 351         determines which queued command was active (if any), and calls
 352         ata_host_intr(ap,qc).
 353         </para>
 354         <para>
 355         Most legacy IDE drivers use ata_bmdma_irq_clear() for the
 356         irq_clear() hook, which simply clears the interrupt and error
 357         flags in the DMA status register.
 358         </para>
 359
 360         </sect2>
 361
 362         <sect2><title>SATA phy read/write</title>
 363         <programlisting>
 364 u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
 365 void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
 366                    u32 val);
 367         </programlisting>
 368
 369         <para>
 370         Read and write standard SATA phy registers.  Currently only used
 371         if ->phy_reset hook called the sata_phy_reset() helper function.
 372         sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
 373         </para>
 374
 375         </sect2>
 376
 377         <sect2><title>Init and shutdown</title>
 378         <programlisting>
 379 int (*port_start) (struct ata_port *ap);
 380 void (*port_stop) (struct ata_port *ap);
 381 void (*host_stop) (struct ata_host_set *host_set);
 382         </programlisting>
 383
 384         <para>
 385         ->port_start() is called just after the data structures for each
 386         port are initialized.  Typically this is used to alloc per-port
 387         DMA buffers / tables / rings, enable DMA engines, and similar
 388         tasks.  Some drivers also use this entry point as a chance to
 389         allocate driver-private memory for ap->private_data.
 390         </para>
 391         <para>
 392         Many drivers use ata_port_start() as this hook or call
 393         it from their own port_start() hooks.  ata_port_start()
 394         allocates space for a legacy IDE PRD table and returns.
 395         </para>
 396         <para>
 397         ->port_stop() is called after ->host_stop().  It's sole function
 398         is to release DMA/memory resources, now that they are no longer
 399         actively being used.  Many drivers also free driver-private
 400         data from port at this time.
 401         </para>
 402         <para>
 403         Many drivers use ata_port_stop() as this hook, which frees the
 404         PRD table.
 405         </para>
 406         <para>
 407         ->host_stop() is called after all ->port_stop() calls
 408 have completed.  The hook must finalize hardware shutdown, release DMA
 409 and other resources, etc.
 410         This hook may be specified as NULL, in which case it is not called.
 411         </para>
 412
 413         </sect2>
 414
 415      </sect1>
 416   </chapter>
 417
 418   <chapter id="libataExt">
 419      <title>libata Library</title>
 420 !Edrivers/scsi/libata-core.c
 421   </chapter>
 422
 423   <chapter id="libataInt">
 424      <title>libata Core Internals</title>
 425 !Idrivers/scsi/libata-core.c
 426   </chapter>
 427
 428   <chapter id="libataScsiInt">
 429      <title>libata SCSI translation/emulation</title>
 430 !Edrivers/scsi/libata-scsi.c
 431 !Idrivers/scsi/libata-scsi.c
 432   </chapter>
 433
 434   <chapter id="PiixInt">
 435      <title>ata_piix Internals</title>
 436 !Idrivers/scsi/ata_piix.c
 437   </chapter>
 438
 439   <chapter id="SILInt">
 440      <title>sata_sil Internals</title>
 441 !Idrivers/scsi/sata_sil.c
 442   </chapter>
 443
 444   <chapter id="libataThanks">
 445      <title>Thanks</title>
 446   <para>
 447   The bulk of the ATA knowledge comes thanks to long conversations with
 448   Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
 449   and SCSI specifications.
 450   </para>
 451   <para>
 452   Thanks to Alan Cox for pointing out similarities
 453   between SATA and SCSI, and in general for motivation to hack on
 454   libata.
 455   </para>
 456   <para>
 457   libata's device detection
 458   method, ata_pio_devchk, and in general all the early probing was
 459   based on extensive study of Hale Landis's probe/reset code in his
 460   ATADRVR driver (www.ata-atapi.com).
 461   </para>
 462   </chapter>
 463
 464 </book>