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://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>PIO data read/write</title>
 173         <programlisting>
 174 void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
 175         </programlisting>
 176
 177         <para>
 178 All bmdma-style drivers must implement this hook.  This is the low-level
 179 operation that actually copies the data bytes during a PIO data
 180 transfer.
 181 Typically the driver
 182 will choose one of ata_pio_data_xfer_noirq(), ata_pio_data_xfer(), or
 183 ata_mmio_data_xfer().
 184         </para>
 185
 186         </sect2>
 187
 188         <sect2><title>ATA command execute</title>
 189         <programlisting>
 190 void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
 191         </programlisting>
 192
 193         <para>
 194         causes an ATA command, previously loaded with
 195         ->tf_load(), to be initiated in hardware.
 196         Most drivers for taskfile-based hardware use ata_exec_command()
 197         for this hook.
 198         </para>
 199
 200         </sect2>
 201
 202         <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
 203         <programlisting>
 204 int (*check_atapi_dma) (struct ata_queued_cmd *qc);
 205         </programlisting>
 206
 207         <para>
 208 Allow low-level driver to filter ATA PACKET commands, returning a status
 209 indicating whether or not it is OK to use DMA for the supplied PACKET
 210 command.
 211         </para>
 212         <para>
 213         This hook may be specified as NULL, in which case libata will
 214         assume that atapi dma can be supported.
 215         </para>
 216
 217         </sect2>
 218
 219         <sect2><title>Read specific ATA shadow registers</title>
 220         <programlisting>
 221 u8   (*check_status)(struct ata_port *ap);
 222 u8   (*check_altstatus)(struct ata_port *ap);
 223         </programlisting>
 224
 225         <para>
 226         Reads the Status/AltStatus ATA shadow register from
 227         hardware.  On some hardware, reading the Status register has
 228         the side effect of clearing the interrupt condition.
 229         Most drivers for taskfile-based hardware use
 230         ata_check_status() for this hook.
 231         </para>
 232         <para>
 233         Note that because this is called from ata_device_add(), at
 234         least a dummy function that clears device interrupts must be
 235         provided for all drivers, even if the controller doesn't
 236         actually have a taskfile status register.
 237         </para>
 238
 239         </sect2>
 240
 241         <sect2><title>Select ATA device on bus</title>
 242         <programlisting>
 243 void (*dev_select)(struct ata_port *ap, unsigned int device);
 244         </programlisting>
 245
 246         <para>
 247         Issues the low-level hardware command(s) that causes one of N
 248         hardware devices to be considered 'selected' (active and
 249         available for use) on the ATA bus.  This generally has no
 250         meaning on FIS-based devices.
 251         </para>
 252         <para>
 253         Most drivers for taskfile-based hardware use
 254         ata_std_dev_select() for this hook.  Controllers which do not
 255         support second drives on a port (such as SATA contollers) will
 256         use ata_noop_dev_select().
 257         </para>
 258
 259         </sect2>
 260
 261         <sect2><title>Private tuning method</title>
 262         <programlisting>
 263 void (*set_mode) (struct ata_port *ap);
 264         </programlisting>
 265
 266         <para>
 267         By default libata performs drive and controller tuning in
 268         accordance with the ATA timing rules and also applies blacklists
 269         and cable limits. Some controllers need special handling and have
 270         custom tuning rules, typically raid controllers that use ATA
 271         commands but do not actually do drive timing.
 272         </para>
 273
 274         <warning>
 275         <para>
 276         This hook should not be used to replace the standard controller
 277         tuning logic when a controller has quirks. Replacing the default
 278         tuning logic in that case would bypass handling for drive and
 279         bridge quirks that may be important to data reliability. If a
 280         controller needs to filter the mode selection it should use the
 281         mode_filter hook instead.
 282         </para>
 283         </warning>
 284
 285         </sect2>
 286
 287         <sect2><title>Control PCI IDE BMDMA engine</title>
 288         <programlisting>
 289 void (*bmdma_setup) (struct ata_queued_cmd *qc);
 290 void (*bmdma_start) (struct ata_queued_cmd *qc);
 291 void (*bmdma_stop) (struct ata_port *ap);
 292 u8   (*bmdma_status) (struct ata_port *ap);
 293         </programlisting>
 294
 295         <para>
 296 When setting up an IDE BMDMA transaction, these hooks arm
 297 (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
 298 the hardware's DMA engine.  ->bmdma_status is used to read the standard
 299 PCI IDE DMA Status register.
 300         </para>
 301
 302         <para>
 303 These hooks are typically either no-ops, or simply not implemented, in
 304 FIS-based drivers.
 305         </para>
 306         <para>
 307 Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
 308 hook.  ata_bmdma_setup() will write the pointer to the PRD table to
 309 the IDE PRD Table Address register, enable DMA in the DMA Command
 310 register, and call exec_command() to begin the transfer.
 311         </para>
 312         <para>
 313 Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
 314 hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
 315 Command register.
 316         </para>
 317         <para>
 318 Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
 319 hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
 320 command register.
 321         </para>
 322         <para>
 323 Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
 324         </para>
 325
 326         </sect2>
 327
 328         <sect2><title>High-level taskfile hooks</title>
 329         <programlisting>
 330 void (*qc_prep) (struct ata_queued_cmd *qc);
 331 int (*qc_issue) (struct ata_queued_cmd *qc);
 332         </programlisting>
 333
 334         <para>
 335         Higher-level hooks, these two hooks can potentially supercede
 336         several of the above taskfile/DMA engine hooks.  ->qc_prep is
 337         called after the buffers have been DMA-mapped, and is typically
 338         used to populate the hardware's DMA scatter-gather table.
 339         Most drivers use the standard ata_qc_prep() helper function, but
 340         more advanced drivers roll their own.
 341         </para>
 342         <para>
 343         ->qc_issue is used to make a command active, once the hardware
 344         and S/G tables have been prepared.  IDE BMDMA drivers use the
 345         helper function ata_qc_issue_prot() for taskfile protocol-based
 346         dispatch.  More advanced drivers implement their own ->qc_issue.
 347         </para>
 348         <para>
 349         ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
 350         ->bmdma_start() as necessary to initiate a transfer.
 351         </para>
 352
 353         </sect2>
 354
 355         <sect2><title>Exception and probe handling (EH)</title>
 356         <programlisting>
 357 void (*eng_timeout) (struct ata_port *ap);
 358 void (*phy_reset) (struct ata_port *ap);
 359         </programlisting>
 360
 361         <para>
 362 Deprecated.  Use ->error_handler() instead.
 363         </para>
 364
 365         <programlisting>
 366 void (*freeze) (struct ata_port *ap);
 367 void (*thaw) (struct ata_port *ap);
 368         </programlisting>
 369
 370         <para>
 371 ata_port_freeze() is called when HSM violations or some other
 372 condition disrupts normal operation of the port.  A frozen port
 373 is not allowed to perform any operation until the port is
 374 thawed, which usually follows a successful reset.
 375         </para>
 376
 377         <para>
 378 The optional ->freeze() callback can be used for freezing the port
 379 hardware-wise (e.g. mask interrupt and stop DMA engine).  If a
 380 port cannot be frozen hardware-wise, the interrupt handler
 381 must ack and clear interrupts unconditionally while the port
 382 is frozen.
 383         </para>
 384         <para>
 385 The optional ->thaw() callback is called to perform the opposite of ->freeze():
 386 prepare the port for normal operation once again.  Unmask interrupts,
 387 start DMA engine, etc.
 388         </para>
 389
 390         <programlisting>
 391 void (*error_handler) (struct ata_port *ap);
 392         </programlisting>
 393
 394         <para>
 395 ->error_handler() is a driver's hook into probe, hotplug, and recovery
 396 and other exceptional conditions.  The primary responsibility of an
 397 implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set
 398 of EH hooks as arguments:
 399         </para>
 400
 401         <para>
 402 'prereset' hook (may be NULL) is called during an EH reset, before any other actions
 403 are taken.
 404         </para>
 405
 406         <para>
 407 'postreset' hook (may be NULL) is called after the EH reset is performed.  Based on
 408 existing conditions, severity of the problem, and hardware capabilities,
 409         </para>
 410
 411         <para>
 412 Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be
 413 called to perform the low-level EH reset.
 414         </para>
 415
 416         <programlisting>
 417 void (*post_internal_cmd) (struct ata_queued_cmd *qc);
 418         </programlisting>
 419
 420         <para>
 421 Perform any hardware-specific actions necessary to finish processing
 422 after executing a probe-time or EH-time command via ata_exec_internal().
 423         </para>
 424
 425         </sect2>
 426
 427         <sect2><title>Hardware interrupt handling</title>
 428         <programlisting>
 429 irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
 430 void (*irq_clear) (struct ata_port *);
 431         </programlisting>
 432
 433         <para>
 434         ->irq_handler is the interrupt handling routine registered with
 435         the system, by libata.  ->irq_clear is called during probe just
 436         before the interrupt handler is registered, to be sure hardware
 437         is quiet.
 438         </para>
 439         <para>
 440         The second argument, dev_instance, should be cast to a pointer
 441         to struct ata_host_set.
 442         </para>
 443         <para>
 444         Most legacy IDE drivers use ata_interrupt() for the
 445         irq_handler hook, which scans all ports in the host_set,
 446         determines which queued command was active (if any), and calls
 447         ata_host_intr(ap,qc).
 448         </para>
 449         <para>
 450         Most legacy IDE drivers use ata_bmdma_irq_clear() for the
 451         irq_clear() hook, which simply clears the interrupt and error
 452         flags in the DMA status register.
 453         </para>
 454
 455         </sect2>
 456
 457         <sect2><title>SATA phy read/write</title>
 458         <programlisting>
 459 int (*scr_read) (struct ata_port *ap, unsigned int sc_reg,
 460                  u32 *val);
 461 int (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
 462                    u32 val);
 463         </programlisting>
 464
 465         <para>
 466         Read and write standard SATA phy registers.  Currently only used
 467         if ->phy_reset hook called the sata_phy_reset() helper function.
 468         sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
 469         </para>
 470
 471         </sect2>
 472
 473         <sect2><title>Init and shutdown</title>
 474         <programlisting>
 475 int (*port_start) (struct ata_port *ap);
 476 void (*port_stop) (struct ata_port *ap);
 477 void (*host_stop) (struct ata_host_set *host_set);
 478         </programlisting>
 479
 480         <para>
 481         ->port_start() is called just after the data structures for each
 482         port are initialized.  Typically this is used to alloc per-port
 483         DMA buffers / tables / rings, enable DMA engines, and similar
 484         tasks.  Some drivers also use this entry point as a chance to
 485         allocate driver-private memory for ap->private_data.
 486         </para>
 487         <para>
 488         Many drivers use ata_port_start() as this hook or call
 489         it from their own port_start() hooks.  ata_port_start()
 490         allocates space for a legacy IDE PRD table and returns.
 491         </para>
 492         <para>
 493         ->port_stop() is called after ->host_stop().  It's sole function
 494         is to release DMA/memory resources, now that they are no longer
 495         actively being used.  Many drivers also free driver-private
 496         data from port at this time.
 497         </para>
 498         <para>
 499         Many drivers use ata_port_stop() as this hook, which frees the
 500         PRD table.
 501         </para>
 502         <para>
 503         ->host_stop() is called after all ->port_stop() calls
 504 have completed.  The hook must finalize hardware shutdown, release DMA
 505 and other resources, etc.
 506         This hook may be specified as NULL, in which case it is not called.
 507         </para>
 508
 509         </sect2>
 510
 511      </sect1>
 512   </chapter>
 513
 514   <chapter id="libataEH">
 515         <title>Error handling</title>
 516
 517         <para>
 518         This chapter describes how errors are handled under libata.
 519         Readers are advised to read SCSI EH
 520         (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first.
 521         </para>
 522
 523         <sect1><title>Origins of commands</title>
 524         <para>
 525         In libata, a command is represented with struct ata_queued_cmd
 526         or qc.  qc's are preallocated during port initialization and
 527         repetitively used for command executions.  Currently only one
 528         qc is allocated per port but yet-to-be-merged NCQ branch
 529         allocates one for each tag and maps each qc to NCQ tag 1-to-1.
 530         </para>
 531         <para>
 532         libata commands can originate from two sources - libata itself
 533         and SCSI midlayer.  libata internal commands are used for
 534         initialization and error handling.  All normal blk requests
 535         and commands for SCSI emulation are passed as SCSI commands
 536         through queuecommand callback of SCSI host template.
 537         </para>
 538         </sect1>
 539
 540         <sect1><title>How commands are issued</title>
 541
 542         <variablelist>
 543
 544         <varlistentry><term>Internal commands</term>
 545         <listitem>
 546         <para>
 547         First, qc is allocated and initialized using
 548         ata_qc_new_init().  Although ata_qc_new_init() doesn't
 549         implement any wait or retry mechanism when qc is not
 550         available, internal commands are currently issued only during
 551         initialization and error recovery, so no other command is
 552         active and allocation is guaranteed to succeed.
 553         </para>
 554         <para>
 555         Once allocated qc's taskfile is initialized for the command to
 556         be executed.  qc currently has two mechanisms to notify
 557         completion.  One is via qc->complete_fn() callback and the
 558         other is completion qc->waiting.  qc->complete_fn() callback
 559         is the asynchronous path used by normal SCSI translated
 560         commands and qc->waiting is the synchronous (issuer sleeps in
 561         process context) path used by internal commands.
 562         </para>
 563         <para>
 564         Once initialization is complete, host_set lock is acquired
 565         and the qc is issued.
 566         </para>
 567         </listitem>
 568         </varlistentry>
 569
 570         <varlistentry><term>SCSI commands</term>
 571         <listitem>
 572         <para>
 573         All libata drivers use ata_scsi_queuecmd() as
 574         hostt->queuecommand callback.  scmds can either be simulated
 575         or translated.  No qc is involved in processing a simulated
 576         scmd.  The result is computed right away and the scmd is
 577         completed.
 578         </para>
 579         <para>
 580         For a translated scmd, ata_qc_new_init() is invoked to
 581         allocate a qc and the scmd is translated into the qc.  SCSI
 582         midlayer's completion notification function pointer is stored
 583         into qc->scsidone.
 584         </para>
 585         <para>
 586         qc->complete_fn() callback is used for completion
 587         notification.  ATA commands use ata_scsi_qc_complete() while
 588         ATAPI commands use atapi_qc_complete().  Both functions end up
 589         calling qc->scsidone to notify upper layer when the qc is
 590         finished.  After translation is completed, the qc is issued
 591         with ata_qc_issue().
 592         </para>
 593         <para>
 594         Note that SCSI midlayer invokes hostt->queuecommand while
 595         holding host_set lock, so all above occur while holding
 596         host_set lock.
 597         </para>
 598         </listitem>
 599         </varlistentry>
 600
 601         </variablelist>
 602         </sect1>
 603
 604         <sect1><title>How commands are processed</title>
 605         <para>
 606         Depending on which protocol and which controller are used,
 607         commands are processed differently.  For the purpose of
 608         discussion, a controller which uses taskfile interface and all
 609         standard callbacks is assumed.
 610         </para>
 611         <para>
 612         Currently 6 ATA command protocols are used.  They can be
 613         sorted into the following four categories according to how
 614         they are processed.
 615         </para>
 616
 617         <variablelist>
 618            <varlistentry><term>ATA NO DATA or DMA</term>
 619            <listitem>
 620            <para>
 621            ATA_PROT_NODATA and ATA_PROT_DMA fall into this category.
 622            These types of commands don't require any software
 623            intervention once issued.  Device will raise interrupt on
 624            completion.
 625            </para>
 626            </listitem>
 627            </varlistentry>
 628
 629            <varlistentry><term>ATA PIO</term>
 630            <listitem>
 631            <para>
 632            ATA_PROT_PIO is in this category.  libata currently
 633            implements PIO with polling.  ATA_NIEN bit is set to turn
 634            off interrupt and pio_task on ata_wq performs polling and
 635            IO.
 636            </para>
 637            </listitem>
 638            </varlistentry>
 639
 640            <varlistentry><term>ATAPI NODATA or DMA</term>
 641            <listitem>
 642            <para>
 643            ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this
 644            category.  packet_task is used to poll BSY bit after
 645            issuing PACKET command.  Once BSY is turned off by the
 646            device, packet_task transfers CDB and hands off processing
 647            to interrupt handler.
 648            </para>
 649            </listitem>
 650            </varlistentry>
 651
 652            <varlistentry><term>ATAPI PIO</term>
 653            <listitem>
 654            <para>
 655            ATA_PROT_ATAPI is in this category.  ATA_NIEN bit is set
 656            and, as in ATAPI NODATA or DMA, packet_task submits cdb.
 657            However, after submitting cdb, further processing (data
 658            transfer) is handed off to pio_task.
 659            </para>
 660            </listitem>
 661            </varlistentry>
 662         </variablelist>
 663         </sect1>
 664
 665         <sect1><title>How commands are completed</title>
 666         <para>
 667         Once issued, all qc's are either completed with
 668         ata_qc_complete() or time out.  For commands which are handled
 669         by interrupts, ata_host_intr() invokes ata_qc_complete(), and,
 670         for PIO tasks, pio_task invokes ata_qc_complete().  In error
 671         cases, packet_task may also complete commands.
 672         </para>
 673         <para>
 674         ata_qc_complete() does the following.
 675         </para>
 676
 677         <orderedlist>
 678
 679         <listitem>
 680         <para>
 681         DMA memory is unmapped.
 682         </para>
 683         </listitem>
 684
 685         <listitem>
 686         <para>
 687         ATA_QCFLAG_ACTIVE is clared from qc->flags.
 688         </para>
 689         </listitem>
 690
 691         <listitem>
 692         <para>
 693         qc->complete_fn() callback is invoked.  If the return value of
 694         the callback is not zero.  Completion is short circuited and
 695         ata_qc_complete() returns.
 696         </para>
 697         </listitem>
 698
 699         <listitem>
 700         <para>
 701         __ata_qc_complete() is called, which does
 702            <orderedlist>
 703
 704            <listitem>
 705            <para>
 706            qc->flags is cleared to zero.
 707            </para>
 708            </listitem>
 709
 710            <listitem>
 711            <para>
 712            ap->active_tag and qc->tag are poisoned.
 713            </para>
 714            </listitem>
 715
 716            <listitem>
 717            <para>
 718            qc->waiting is claread &amp; completed (in that order).
 719            </para>
 720            </listitem>
 721
 722            <listitem>
 723            <para>
 724            qc is deallocated by clearing appropriate bit in ap->qactive.
 725            </para>
 726            </listitem>
 727
 728            </orderedlist>
 729         </para>
 730         </listitem>
 731
 732         </orderedlist>
 733
 734         <para>
 735         So, it basically notifies upper layer and deallocates qc.  One
 736         exception is short-circuit path in #3 which is used by
 737         atapi_qc_complete().
 738         </para>
 739         <para>
 740         For all non-ATAPI commands, whether it fails or not, almost
 741         the same code path is taken and very little error handling
 742         takes place.  A qc is completed with success status if it
 743         succeeded, with failed status otherwise.
 744         </para>
 745         <para>
 746         However, failed ATAPI commands require more handling as
 747         REQUEST SENSE is needed to acquire sense data.  If an ATAPI
 748         command fails, ata_qc_complete() is invoked with error status,
 749         which in turn invokes atapi_qc_complete() via
 750         qc->complete_fn() callback.
 751         </para>
 752         <para>
 753         This makes atapi_qc_complete() set scmd->result to
 754         SAM_STAT_CHECK_CONDITION, complete the scmd and return 1.  As
 755         the sense data is empty but scmd->result is CHECK CONDITION,
 756         SCSI midlayer will invoke EH for the scmd, and returning 1
 757         makes ata_qc_complete() to return without deallocating the qc.
 758         This leads us to ata_scsi_error() with partially completed qc.
 759         </para>
 760
 761         </sect1>
 762
 763         <sect1><title>ata_scsi_error()</title>
 764         <para>
 765         ata_scsi_error() is the current transportt->eh_strategy_handler()
 766         for libata.  As discussed above, this will be entered in two
 767         cases - timeout and ATAPI error completion.  This function
 768         calls low level libata driver's eng_timeout() callback, the
 769         standard callback for which is ata_eng_timeout().  It checks
 770         if a qc is active and calls ata_qc_timeout() on the qc if so.
 771         Actual error handling occurs in ata_qc_timeout().
 772         </para>
 773         <para>
 774         If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and
 775         completes the qc.  Note that as we're currently in EH, we
 776         cannot call scsi_done.  As described in SCSI EH doc, a
 777         recovered scmd should be either retried with
 778         scsi_queue_insert() or finished with scsi_finish_command().
 779         Here, we override qc->scsidone with scsi_finish_command() and
 780         calls ata_qc_complete().
 781         </para>
 782         <para>
 783         If EH is invoked due to a failed ATAPI qc, the qc here is
 784         completed but not deallocated.  The purpose of this
 785         half-completion is to use the qc as place holder to make EH
 786         code reach this place.  This is a bit hackish, but it works.
 787         </para>
 788         <para>
 789         Once control reaches here, the qc is deallocated by invoking
 790         __ata_qc_complete() explicitly.  Then, internal qc for REQUEST
 791         SENSE is issued.  Once sense data is acquired, scmd is
 792         finished by directly invoking scsi_finish_command() on the
 793         scmd.  Note that as we already have completed and deallocated
 794         the qc which was associated with the scmd, we don't need
 795         to/cannot call ata_qc_complete() again.
 796         </para>
 797
 798         </sect1>
 799
 800         <sect1><title>Problems with the current EH</title>
 801
 802         <itemizedlist>
 803
 804         <listitem>
 805         <para>
 806         Error representation is too crude.  Currently any and all
 807         error conditions are represented with ATA STATUS and ERROR
 808         registers.  Errors which aren't ATA device errors are treated
 809         as ATA device errors by setting ATA_ERR bit.  Better error
 810         descriptor which can properly represent ATA and other
 811         errors/exceptions is needed.
 812         </para>
 813         </listitem>
 814
 815         <listitem>
 816         <para>
 817         When handling timeouts, no action is taken to make device
 818         forget about the timed out command and ready for new commands.
 819         </para>
 820         </listitem>
 821
 822         <listitem>
 823         <para>
 824         EH handling via ata_scsi_error() is not properly protected
 825         from usual command processing.  On EH entrance, the device is
 826         not in quiescent state.  Timed out commands may succeed or
 827         fail any time.  pio_task and atapi_task may still be running.
 828         </para>
 829         </listitem>
 830
 831         <listitem>
 832         <para>
 833         Too weak error recovery.  Devices / controllers causing HSM
 834         mismatch errors and other errors quite often require reset to
 835         return to known state.  Also, advanced error handling is
 836         necessary to support features like NCQ and hotplug.
 837         </para>
 838         </listitem>
 839
 840         <listitem>
 841         <para>
 842         ATA errors are directly handled in the interrupt handler and
 843         PIO errors in pio_task.  This is problematic for advanced
 844         error handling for the following reasons.
 845         </para>
 846         <para>
 847         First, advanced error handling often requires context and
 848         internal qc execution.
 849         </para>
 850         <para>
 851         Second, even a simple failure (say, CRC error) needs
 852         information gathering and could trigger complex error handling
 853         (say, resetting &amp; reconfiguring).  Having multiple code
 854         paths to gather information, enter EH and trigger actions
 855         makes life painful.
 856         </para>
 857         <para>
 858         Third, scattered EH code makes implementing low level drivers
 859         difficult.  Low level drivers override libata callbacks.  If
 860         EH is scattered over several places, each affected callbacks
 861         should perform its part of error handling.  This can be error
 862         prone and painful.
 863         </para>
 864         </listitem>
 865
 866         </itemizedlist>
 867         </sect1>
 868   </chapter>
 869
 870   <chapter id="libataExt">
 871      <title>libata Library</title>
 872 !Edrivers/ata/libata-core.c
 873   </chapter>
 874
 875   <chapter id="libataInt">
 876      <title>libata Core Internals</title>
 877 !Idrivers/ata/libata-core.c
 878   </chapter>
 879
 880   <chapter id="libataScsiInt">
 881      <title>libata SCSI translation/emulation</title>
 882 !Edrivers/ata/libata-scsi.c
 883 !Idrivers/ata/libata-scsi.c
 884   </chapter>
 885
 886   <chapter id="ataExceptions">
 887      <title>ATA errors and exceptions</title>
 888
 889   <para>
 890   This chapter tries to identify what error/exception conditions exist
 891   for ATA/ATAPI devices and describe how they should be handled in
 892   implementation-neutral way.
 893   </para>
 894
 895   <para>
 896   The term 'error' is used to describe conditions where either an
 897   explicit error condition is reported from device or a command has
 898   timed out.
 899   </para>
 900
 901   <para>
 902   The term 'exception' is either used to describe exceptional
 903   conditions which are not errors (say, power or hotplug events), or
 904   to describe both errors and non-error exceptional conditions.  Where
 905   explicit distinction between error and exception is necessary, the
 906   term 'non-error exception' is used.
 907   </para>
 908
 909   <sect1 id="excat">
 910      <title>Exception categories</title>
 911      <para>
 912      Exceptions are described primarily with respect to legacy
 913      taskfile + bus master IDE interface.  If a controller provides
 914      other better mechanism for error reporting, mapping those into
 915      categories described below shouldn't be difficult.
 916      </para>
 917
 918      <para>
 919      In the following sections, two recovery actions - reset and
 920      reconfiguring transport - are mentioned.  These are described
 921      further in <xref linkend="exrec"/>.
 922      </para>
 923
 924      <sect2 id="excatHSMviolation">
 925         <title>HSM violation</title>
 926         <para>
 927         This error is indicated when STATUS value doesn't match HSM
 928         requirement during issuing or excution any ATA/ATAPI command.
 929         </para>
 930
 931         <itemizedlist>
 932         <title>Examples</title>
 933
 934         <listitem>
 935         <para>
 936         ATA_STATUS doesn't contain !BSY &amp;&amp; DRDY &amp;&amp; !DRQ while trying
 937         to issue a command.
 938         </para>
 939         </listitem>
 940
 941         <listitem>
 942         <para>
 943         !BSY &amp;&amp; !DRQ during PIO data transfer.
 944         </para>
 945         </listitem>
 946
 947         <listitem>
 948         <para>
 949         DRQ on command completion.
 950         </para>
 951         </listitem>
 952
 953         <listitem>
 954         <para>
 955         !BSY &amp;&amp; ERR after CDB tranfer starts but before the
 956         last byte of CDB is transferred.  ATA/ATAPI standard states
 957         that &quot;The device shall not terminate the PACKET command
 958         with an error before the last byte of the command packet has
 959         been written&quot; in the error outputs description of PACKET
 960         command and the state diagram doesn't include such
 961         transitions.
 962         </para>
 963         </listitem>
 964
 965         </itemizedlist>
 966
 967         <para>
 968         In these cases, HSM is violated and not much information
 969         regarding the error can be acquired from STATUS or ERROR
 970         register.  IOW, this error can be anything - driver bug,
 971         faulty device, controller and/or cable.
 972         </para>
 973
 974         <para>
 975         As HSM is violated, reset is necessary to restore known state.
 976         Reconfiguring transport for lower speed might be helpful too
 977         as transmission errors sometimes cause this kind of errors.
 978         </para>
 979      </sect2>
 980
 981      <sect2 id="excatDevErr">
 982         <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title>
 983
 984         <para>
 985         These are errors detected and reported by ATA/ATAPI devices
 986         indicating device problems.  For this type of errors, STATUS
 987         and ERROR register values are valid and describe error
 988         condition.  Note that some of ATA bus errors are detected by
 989         ATA/ATAPI devices and reported using the same mechanism as
 990         device errors.  Those cases are described later in this
 991         section.
 992         </para>
 993
 994         <para>
 995         For ATA commands, this type of errors are indicated by !BSY
 996         &amp;&amp; ERR during command execution and on completion.
 997         </para>
 998
 999         <para>For ATAPI commands,</para>
1000
1001         <itemizedlist>
1002
1003         <listitem>
1004         <para>
1005         !BSY &amp;&amp; ERR &amp;&amp; ABRT right after issuing PACKET
1006         indicates that PACKET command is not supported and falls in
1007         this category.
1008         </para>
1009         </listitem>
1010
1011         <listitem>
1012         <para>
1013         !BSY &amp;&amp; ERR(==CHK) &amp;&amp; !ABRT after the last
1014         byte of CDB is transferred indicates CHECK CONDITION and
1015         doesn't fall in this category.
1016         </para>
1017         </listitem>
1018
1019         <listitem>
1020         <para>
1021         !BSY &amp;&amp; ERR(==CHK) &amp;&amp; ABRT after the last byte
1022         of CDB is transferred *probably* indicates CHECK CONDITION and
1023         doesn't fall in this category.
1024         </para>
1025         </listitem>
1026
1027         </itemizedlist>
1028
1029         <para>
1030         Of errors detected as above, the followings are not ATA/ATAPI
1031         device errors but ATA bus errors and should be handled
1032         according to <xref linkend="excatATAbusErr"/>.
1033         </para>
1034
1035         <variablelist>
1036
1037            <varlistentry>
1038            <term>CRC error during data transfer</term>
1039            <listitem>
1040            <para>
1041            This is indicated by ICRC bit in the ERROR register and
1042            means that corruption occurred during data transfer.  Upto
1043            ATA/ATAPI-7, the standard specifies that this bit is only
1044            applicable to UDMA transfers but ATA/ATAPI-8 draft revision
1045            1f says that the bit may be applicable to multiword DMA and
1046            PIO.
1047            </para>
1048            </listitem>
1049            </varlistentry>
1050
1051            <varlistentry>
1052            <term>ABRT error during data transfer or on completion</term>
1053            <listitem>
1054            <para>
1055            Upto ATA/ATAPI-7, the standard specifies that ABRT could be
1056            set on ICRC errors and on cases where a device is not able
1057            to complete a command.  Combined with the fact that MWDMA
1058            and PIO transfer errors aren't allowed to use ICRC bit upto
1059            ATA/ATAPI-7, it seems to imply that ABRT bit alone could
1060            indicate tranfer errors.
1061            </para>
1062            <para>
1063            However, ATA/ATAPI-8 draft revision 1f removes the part
1064            that ICRC errors can turn on ABRT.  So, this is kind of
1065            gray area.  Some heuristics are needed here.
1066            </para>
1067            </listitem>
1068            </varlistentry>
1069
1070         </variablelist>
1071
1072         <para>
1073         ATA/ATAPI device errors can be further categorized as follows.
1074         </para>
1075
1076         <variablelist>
1077
1078            <varlistentry>
1079            <term>Media errors</term>
1080            <listitem>
1081            <para>
1082            This is indicated by UNC bit in the ERROR register.  ATA
1083            devices reports UNC error only after certain number of
1084            retries cannot recover the data, so there's nothing much
1085            else to do other than notifying upper layer.
1086            </para>
1087            <para>
1088            READ and WRITE commands report CHS or LBA of the first
1089            failed sector but ATA/ATAPI standard specifies that the
1090            amount of transferred data on error completion is
1091            indeterminate, so we cannot assume that sectors preceding
1092            the failed sector have been transferred and thus cannot
1093            complete those sectors successfully as SCSI does.
1094            </para>
1095            </listitem>
1096            </varlistentry>
1097
1098            <varlistentry>
1099            <term>Media changed / media change requested error</term>
1100            <listitem>
1101            <para>
1102            &lt;&lt;TODO: fill here&gt;&gt;
1103            </para>
1104            </listitem>
1105            </varlistentry>
1106
1107            <varlistentry><term>Address error</term>
1108            <listitem>
1109            <para>
1110            This is indicated by IDNF bit in the ERROR register.
1111            Report to upper layer.
1112            </para>
1113            </listitem>
1114            </varlistentry>
1115
1116            <varlistentry><term>Other errors</term>
1117            <listitem>
1118            <para>
1119            This can be invalid command or parameter indicated by ABRT
1120            ERROR bit or some other error condition.  Note that ABRT
1121            bit can indicate a lot of things including ICRC and Address
1122            errors.  Heuristics needed.
1123            </para>
1124            </listitem>
1125            </varlistentry>
1126
1127         </variablelist>
1128
1129         <para>
1130         Depending on commands, not all STATUS/ERROR bits are
1131         applicable.  These non-applicable bits are marked with
1132         &quot;na&quot; in the output descriptions but upto ATA/ATAPI-7
1133         no definition of &quot;na&quot; can be found.  However,
1134         ATA/ATAPI-8 draft revision 1f describes &quot;N/A&quot; as
1135         follows.
1136         </para>
1137
1138         <blockquote>
1139         <variablelist>
1140            <varlistentry><term>3.2.3.3a N/A</term>
1141            <listitem>
1142            <para>
1143            A keyword the indicates a field has no defined value in
1144            this standard and should not be checked by the host or
1145            device. N/A fields should be cleared to zero.
1146            </para>
1147            </listitem>
1148            </varlistentry>
1149         </variablelist>
1150         </blockquote>
1151
1152         <para>
1153         So, it seems reasonable to assume that &quot;na&quot; bits are
1154         cleared to zero by devices and thus need no explicit masking.
1155         </para>
1156
1157      </sect2>
1158
1159      <sect2 id="excatATAPIcc">
1160         <title>ATAPI device CHECK CONDITION</title>
1161
1162         <para>
1163         ATAPI device CHECK CONDITION error is indicated by set CHK bit
1164         (ERR bit) in the STATUS register after the last byte of CDB is
1165         transferred for a PACKET command.  For this kind of errors,
1166         sense data should be acquired to gather information regarding
1167         the errors.  REQUEST SENSE packet command should be used to
1168         acquire sense data.
1169         </para>
1170
1171         <para>
1172         Once sense data is acquired, this type of errors can be
1173         handled similary to other SCSI errors.  Note that sense data
1174         may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR
1175         &amp;&amp; ASC/ASCQ 47h/00h SCSI PARITY ERROR).  In such
1176         cases, the error should be considered as an ATA bus error and
1177         handled according to <xref linkend="excatATAbusErr"/>.
1178         </para>
1179
1180      </sect2>
1181
1182      <sect2 id="excatNCQerr">
1183         <title>ATA device error (NCQ)</title>
1184
1185         <para>
1186         NCQ command error is indicated by cleared BSY and set ERR bit
1187         during NCQ command phase (one or more NCQ commands
1188         outstanding).  Although STATUS and ERROR registers will
1189         contain valid values describing the error, READ LOG EXT is
1190         required to clear the error condition, determine which command
1191         has failed and acquire more information.
1192         </para>
1193
1194         <para>
1195         READ LOG EXT Log Page 10h reports which tag has failed and
1196         taskfile register values describing the error.  With this
1197         information the failed command can be handled as a normal ATA
1198         command error as in <xref linkend="excatDevErr"/> and all
1199         other in-flight commands must be retried.  Note that this
1200         retry should not be counted - it's likely that commands
1201         retried this way would have completed normally if it were not
1202         for the failed command.
1203         </para>
1204
1205         <para>
1206         Note that ATA bus errors can be reported as ATA device NCQ
1207         errors.  This should be handled as described in <xref
1208         linkend="excatATAbusErr"/>.
1209         </para>
1210
1211         <para>
1212         If READ LOG EXT Log Page 10h fails or reports NQ, we're
1213         thoroughly screwed.  This condition should be treated
1214         according to <xref linkend="excatHSMviolation"/>.
1215         </para>
1216
1217      </sect2>
1218
1219      <sect2 id="excatATAbusErr">
1220         <title>ATA bus error</title>
1221
1222         <para>
1223         ATA bus error means that data corruption occurred during
1224         transmission over ATA bus (SATA or PATA).  This type of errors
1225         can be indicated by
1226         </para>
1227
1228         <itemizedlist>
1229
1230         <listitem>
1231         <para>
1232         ICRC or ABRT error as described in <xref linkend="excatDevErr"/>.
1233         </para>
1234         </listitem>
1235
1236         <listitem>
1237         <para>
1238         Controller-specific error completion with error information
1239         indicating transmission error.
1240         </para>
1241         </listitem>
1242
1243         <listitem>
1244         <para>
1245         On some controllers, command timeout.  In this case, there may
1246         be a mechanism to determine that the timeout is due to
1247         transmission error.
1248         </para>
1249         </listitem>
1250
1251         <listitem>
1252         <para>
1253         Unknown/random errors, timeouts and all sorts of weirdities.
1254         </para>
1255         </listitem>
1256
1257         </itemizedlist>
1258
1259         <para>
1260         As described above, transmission errors can cause wide variety
1261         of symptoms ranging from device ICRC error to random device
1262         lockup, and, for many cases, there is no way to tell if an
1263         error condition is due to transmission error or not;
1264         therefore, it's necessary to employ some kind of heuristic
1265         when dealing with errors and timeouts.  For example,
1266         encountering repetitive ABRT errors for known supported
1267         command is likely to indicate ATA bus error.
1268         </para>
1269
1270         <para>
1271         Once it's determined that ATA bus errors have possibly
1272         occurred, lowering ATA bus transmission speed is one of
1273         actions which may alleviate the problem.  See <xref
1274         linkend="exrecReconf"/> for more information.
1275         </para>
1276
1277      </sect2>
1278
1279      <sect2 id="excatPCIbusErr">
1280         <title>PCI bus error</title>
1281
1282         <para>
1283         Data corruption or other failures during transmission over PCI
1284         (or other system bus).  For standard BMDMA, this is indicated
1285         by Error bit in the BMDMA Status register.  This type of
1286         errors must be logged as it indicates something is very wrong
1287         with the system.  Resetting host controller is recommended.
1288         </para>
1289
1290      </sect2>
1291
1292      <sect2 id="excatLateCompletion">
1293         <title>Late completion</title>
1294
1295         <para>
1296         This occurs when timeout occurs and the timeout handler finds
1297         out that the timed out command has completed successfully or
1298         with error.  This is usually caused by lost interrupts.  This
1299         type of errors must be logged.  Resetting host controller is
1300         recommended.
1301         </para>
1302
1303      </sect2>
1304
1305      <sect2 id="excatUnknown">
1306         <title>Unknown error (timeout)</title>
1307
1308         <para>
1309         This is when timeout occurs and the command is still
1310         processing or the host and device are in unknown state.  When
1311         this occurs, HSM could be in any valid or invalid state.  To
1312         bring the device to known state and make it forget about the
1313         timed out command, resetting is necessary.  The timed out
1314         command may be retried.
1315         </para>
1316
1317         <para>
1318         Timeouts can also be caused by transmission errors.  Refer to
1319         <xref linkend="excatATAbusErr"/> for more details.
1320         </para>
1321
1322      </sect2>
1323
1324      <sect2 id="excatHoplugPM">
1325         <title>Hotplug and power management exceptions</title>
1326
1327         <para>
1328         &lt;&lt;TODO: fill here&gt;&gt;
1329         </para>
1330
1331      </sect2>
1332
1333   </sect1>
1334
1335   <sect1 id="exrec">
1336      <title>EH recovery actions</title>
1337
1338      <para>
1339      This section discusses several important recovery actions.
1340      </para>
1341
1342      <sect2 id="exrecClr">
1343         <title>Clearing error condition</title>
1344
1345         <para>
1346         Many controllers require its error registers to be cleared by
1347         error handler.  Different controllers may have different
1348         requirements.
1349         </para>
1350
1351         <para>
1352         For SATA, it's strongly recommended to clear at least SError
1353         register during error handling.
1354         </para>
1355      </sect2>
1356
1357      <sect2 id="exrecRst">
1358         <title>Reset</title>
1359
1360         <para>
1361         During EH, resetting is necessary in the following cases.
1362         </para>
1363
1364         <itemizedlist>
1365
1366         <listitem>
1367         <para>
1368         HSM is in unknown or invalid state
1369         </para>
1370         </listitem>
1371
1372         <listitem>
1373         <para>
1374         HBA is in unknown or invalid state
1375         </para>
1376         </listitem>
1377
1378         <listitem>
1379         <para>
1380         EH needs to make HBA/device forget about in-flight commands
1381         </para>
1382         </listitem>
1383
1384         <listitem>
1385         <para>
1386         HBA/device behaves weirdly
1387         </para>
1388         </listitem>
1389
1390         </itemizedlist>
1391
1392         <para>
1393         Resetting during EH might be a good idea regardless of error
1394         condition to improve EH robustness.  Whether to reset both or
1395         either one of HBA and device depends on situation but the
1396         following scheme is recommended.
1397         </para>
1398
1399         <itemizedlist>
1400
1401         <listitem>
1402         <para>
1403         When it's known that HBA is in ready state but ATA/ATAPI
1404         device is in unknown state, reset only device.
1405         </para>
1406         </listitem>
1407
1408         <listitem>
1409         <para>
1410         If HBA is in unknown state, reset both HBA and device.
1411         </para>
1412         </listitem>
1413
1414         </itemizedlist>
1415
1416         <para>
1417         HBA resetting is implementation specific.  For a controller
1418         complying to taskfile/BMDMA PCI IDE, stopping active DMA
1419         transaction may be sufficient iff BMDMA state is the only HBA
1420         context.  But even mostly taskfile/BMDMA PCI IDE complying
1421         controllers may have implementation specific requirements and
1422         mechanism to reset themselves.  This must be addressed by
1423         specific drivers.
1424         </para>
1425
1426         <para>
1427         OTOH, ATA/ATAPI standard describes in detail ways to reset
1428         ATA/ATAPI devices.
1429         </para>
1430
1431         <variablelist>
1432
1433            <varlistentry><term>PATA hardware reset</term>
1434            <listitem>
1435            <para>
1436            This is hardware initiated device reset signalled with
1437            asserted PATA RESET- signal.  There is no standard way to
1438            initiate hardware reset from software although some
1439            hardware provides registers that allow driver to directly
1440            tweak the RESET- signal.
1441            </para>
1442            </listitem>
1443            </varlistentry>
1444
1445            <varlistentry><term>Software reset</term>
1446            <listitem>
1447            <para>
1448            This is achieved by turning CONTROL SRST bit on for at
1449            least 5us.  Both PATA and SATA support it but, in case of
1450            SATA, this may require controller-specific support as the
1451            second Register FIS to clear SRST should be transmitted
1452            while BSY bit is still set.  Note that on PATA, this resets
1453            both master and slave devices on a channel.
1454            </para>
1455            </listitem>
1456            </varlistentry>
1457
1458            <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term>
1459            <listitem>
1460            <para>
1461            Although ATA/ATAPI standard doesn't describe exactly, EDD
1462            implies some level of resetting, possibly similar level
1463            with software reset.  Host-side EDD protocol can be handled
1464            with normal command processing and most SATA controllers
1465            should be able to handle EDD's just like other commands.
1466            As in software reset, EDD affects both devices on a PATA
1467            bus.
1468            </para>
1469            <para>
1470            Although EDD does reset devices, this doesn't suit error
1471            handling as EDD cannot be issued while BSY is set and it's
1472            unclear how it will act when device is in unknown/weird
1473            state.
1474            </para>
1475            </listitem>
1476            </varlistentry>
1477
1478            <varlistentry><term>ATAPI DEVICE RESET command</term>
1479            <listitem>
1480            <para>
1481            This is very similar to software reset except that reset
1482            can be restricted to the selected device without affecting
1483            the other device sharing the cable.
1484            </para>
1485            </listitem>
1486            </varlistentry>
1487
1488            <varlistentry><term>SATA phy reset</term>
1489            <listitem>
1490            <para>
1491            This is the preferred way of resetting a SATA device.  In
1492            effect, it's identical to PATA hardware reset.  Note that
1493            this can be done with the standard SCR Control register.
1494            As such, it's usually easier to implement than software
1495            reset.
1496            </para>
1497            </listitem>
1498            </varlistentry>
1499
1500         </variablelist>
1501
1502         <para>
1503         One more thing to consider when resetting devices is that
1504         resetting clears certain configuration parameters and they
1505         need to be set to their previous or newly adjusted values
1506         after reset.
1507         </para>
1508
1509         <para>
1510         Parameters affected are.
1511         </para>
1512
1513         <itemizedlist>
1514
1515         <listitem>
1516         <para>
1517         CHS set up with INITIALIZE DEVICE PARAMETERS (seldomly used)
1518         </para>
1519         </listitem>
1520
1521         <listitem>
1522         <para>
1523         Parameters set with SET FEATURES including transfer mode setting
1524         </para>
1525         </listitem>
1526
1527         <listitem>
1528         <para>
1529         Block count set with SET MULTIPLE MODE
1530         </para>
1531         </listitem>
1532
1533         <listitem>
1534         <para>
1535         Other parameters (SET MAX, MEDIA LOCK...)
1536         </para>
1537         </listitem>
1538
1539         </itemizedlist>
1540
1541         <para>
1542         ATA/ATAPI standard specifies that some parameters must be
1543         maintained across hardware or software reset, but doesn't
1544         strictly specify all of them.  Always reconfiguring needed
1545         parameters after reset is required for robustness.  Note that
1546         this also applies when resuming from deep sleep (power-off).
1547         </para>
1548
1549         <para>
1550         Also, ATA/ATAPI standard requires that IDENTIFY DEVICE /
1551         IDENTIFY PACKET DEVICE is issued after any configuration
1552         parameter is updated or a hardware reset and the result used
1553         for further operation.  OS driver is required to implement
1554         revalidation mechanism to support this.
1555         </para>
1556
1557      </sect2>
1558
1559      <sect2 id="exrecReconf">
1560         <title>Reconfigure transport</title>
1561
1562         <para>
1563         For both PATA and SATA, a lot of corners are cut for cheap
1564         connectors, cables or controllers and it's quite common to see
1565         high transmission error rate.  This can be mitigated by
1566         lowering transmission speed.
1567         </para>
1568
1569         <para>
1570         The following is a possible scheme Jeff Garzik suggested.
1571         </para>
1572
1573         <blockquote>
1574         <para>
1575         If more than $N (3?) transmission errors happen in 15 minutes,
1576         </para>
1577         <itemizedlist>
1578         <listitem>
1579         <para>
1580         if SATA, decrease SATA PHY speed.  if speed cannot be decreased,
1581         </para>
1582         </listitem>
1583         <listitem>
1584         <para>
1585         decrease UDMA xfer speed.  if at UDMA0, switch to PIO4,
1586         </para>
1587         </listitem>
1588         <listitem>
1589         <para>
1590         decrease PIO xfer speed.  if at PIO3, complain, but continue
1591         </para>
1592         </listitem>
1593         </itemizedlist>
1594         </blockquote>
1595
1596      </sect2>
1597
1598   </sect1>
1599
1600   </chapter>
1601
1602   <chapter id="PiixInt">
1603      <title>ata_piix Internals</title>
1604 !Idrivers/ata/ata_piix.c
1605   </chapter>
1606
1607   <chapter id="SILInt">
1608      <title>sata_sil Internals</title>
1609 !Idrivers/ata/sata_sil.c
1610   </chapter>
1611
1612   <chapter id="libataThanks">
1613      <title>Thanks</title>
1614   <para>
1615   The bulk of the ATA knowledge comes thanks to long conversations with
1616   Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
1617   and SCSI specifications.
1618   </para>
1619   <para>
1620   Thanks to Alan Cox for pointing out similarities
1621   between SATA and SCSI, and in general for motivation to hack on
1622   libata.
1623   </para>
1624   <para>
1625   libata's device detection
1626   method, ata_pio_devchk, and in general all the early probing was
1627   based on extensive study of Hale Landis's probe/reset code in his
1628   ATADRVR driver (www.ata-atapi.com).
1629   </para>
1630   </chapter>
1631
1632 </book>