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authorFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
committerFathi Boudra <fathi.boudra@linaro.org>2013-04-28 09:33:08 +0300
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treeb9996006addfd7ae70a39672b76843b49aebc189 /Documentation/DocBook/libata.tmpl
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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="libataDevGuide">
+ <bookinfo>
+ <title>libATA Developer's Guide</title>
+
+ <authorgroup>
+ <author>
+ <firstname>Jeff</firstname>
+ <surname>Garzik</surname>
+ </author>
+ </authorgroup>
+
+ <copyright>
+ <year>2003-2006</year>
+ <holder>Jeff Garzik</holder>
+ </copyright>
+
+ <legalnotice>
+ <para>
+ The contents of this file are subject to the Open
+ Software License version 1.1 that can be found at
+ <ulink url="http://fedoraproject.org/wiki/Licensing:OSL1.1">http://fedoraproject.org/wiki/Licensing:OSL1.1</ulink>
+ and is included herein by reference.
+ </para>
+
+ <para>
+ Alternatively, the contents of this file may be used under the terms
+ of the GNU General Public License version 2 (the "GPL") as distributed
+ in the kernel source COPYING file, in which case the provisions of
+ the GPL are applicable instead of the above. If you wish to allow
+ the use of your version of this file only under the terms of the
+ GPL and not to allow others to use your version of this file under
+ the OSL, indicate your decision by deleting the provisions above and
+ replace them with the notice and other provisions required by the GPL.
+ If you do not delete the provisions above, a recipient may use your
+ version of this file under either the OSL or the GPL.
+ </para>
+
+ </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+ <chapter id="libataIntroduction">
+ <title>Introduction</title>
+ <para>
+ libATA is a library used inside the Linux kernel to support ATA host
+ controllers and devices. libATA provides an ATA driver API, class
+ transports for ATA and ATAPI devices, and SCSI&lt;-&gt;ATA translation
+ for ATA devices according to the T10 SAT specification.
+ </para>
+ <para>
+ This Guide documents the libATA driver API, library functions, library
+ internals, and a couple sample ATA low-level drivers.
+ </para>
+ </chapter>
+
+ <chapter id="libataDriverApi">
+ <title>libata Driver API</title>
+ <para>
+ struct ata_port_operations is defined for every low-level libata
+ hardware driver, and it controls how the low-level driver
+ interfaces with the ATA and SCSI layers.
+ </para>
+ <para>
+ FIS-based drivers will hook into the system with ->qc_prep() and
+ ->qc_issue() high-level hooks. Hardware which behaves in a manner
+ similar to PCI IDE hardware may utilize several generic helpers,
+ defining at a bare minimum the bus I/O addresses of the ATA shadow
+ register blocks.
+ </para>
+ <sect1>
+ <title>struct ata_port_operations</title>
+
+ <sect2><title>Disable ATA port</title>
+ <programlisting>
+void (*port_disable) (struct ata_port *);
+ </programlisting>
+
+ <para>
+ Called from ata_bus_probe() error path, as well as when
+ unregistering from the SCSI module (rmmod, hot unplug).
+ This function should do whatever needs to be done to take the
+ port out of use. In most cases, ata_port_disable() can be used
+ as this hook.
+ </para>
+ <para>
+ Called from ata_bus_probe() on a failed probe.
+ Called from ata_scsi_release().
+ </para>
+
+ </sect2>
+
+ <sect2><title>Post-IDENTIFY device configuration</title>
+ <programlisting>
+void (*dev_config) (struct ata_port *, struct ata_device *);
+ </programlisting>
+
+ <para>
+ Called after IDENTIFY [PACKET] DEVICE is issued to each device
+ found. Typically used to apply device-specific fixups prior to
+ issue of SET FEATURES - XFER MODE, and prior to operation.
+ </para>
+ <para>
+ This entry may be specified as NULL in ata_port_operations.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Set PIO/DMA mode</title>
+ <programlisting>
+void (*set_piomode) (struct ata_port *, struct ata_device *);
+void (*set_dmamode) (struct ata_port *, struct ata_device *);
+void (*post_set_mode) (struct ata_port *);
+unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int);
+ </programlisting>
+
+ <para>
+ Hooks called prior to the issue of SET FEATURES - XFER MODE
+ command. The optional ->mode_filter() hook is called when libata
+ has built a mask of the possible modes. This is passed to the
+ ->mode_filter() function which should return a mask of valid modes
+ after filtering those unsuitable due to hardware limits. It is not
+ valid to use this interface to add modes.
+ </para>
+ <para>
+ dev->pio_mode and dev->dma_mode are guaranteed to be valid when
+ ->set_piomode() and when ->set_dmamode() is called. The timings for
+ any other drive sharing the cable will also be valid at this point.
+ That is the library records the decisions for the modes of each
+ drive on a channel before it attempts to set any of them.
+ </para>
+ <para>
+ ->post_set_mode() is
+ called unconditionally, after the SET FEATURES - XFER MODE
+ command completes successfully.
+ </para>
+
+ <para>
+ ->set_piomode() is always called (if present), but
+ ->set_dma_mode() is only called if DMA is possible.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Taskfile read/write</title>
+ <programlisting>
+void (*sff_tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
+void (*sff_tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
+ </programlisting>
+
+ <para>
+ ->tf_load() is called to load the given taskfile into hardware
+ registers / DMA buffers. ->tf_read() is called to read the
+ hardware registers / DMA buffers, to obtain the current set of
+ taskfile register values.
+ Most drivers for taskfile-based hardware (PIO or MMIO) use
+ ata_sff_tf_load() and ata_sff_tf_read() for these hooks.
+ </para>
+
+ </sect2>
+
+ <sect2><title>PIO data read/write</title>
+ <programlisting>
+void (*sff_data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
+ </programlisting>
+
+ <para>
+All bmdma-style drivers must implement this hook. This is the low-level
+operation that actually copies the data bytes during a PIO data
+transfer.
+Typically the driver will choose one of ata_sff_data_xfer_noirq(),
+ata_sff_data_xfer(), or ata_sff_data_xfer32().
+ </para>
+
+ </sect2>
+
+ <sect2><title>ATA command execute</title>
+ <programlisting>
+void (*sff_exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
+ </programlisting>
+
+ <para>
+ causes an ATA command, previously loaded with
+ ->tf_load(), to be initiated in hardware.
+ Most drivers for taskfile-based hardware use ata_sff_exec_command()
+ for this hook.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
+ <programlisting>
+int (*check_atapi_dma) (struct ata_queued_cmd *qc);
+ </programlisting>
+
+ <para>
+Allow low-level driver to filter ATA PACKET commands, returning a status
+indicating whether or not it is OK to use DMA for the supplied PACKET
+command.
+ </para>
+ <para>
+ This hook may be specified as NULL, in which case libata will
+ assume that atapi dma can be supported.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Read specific ATA shadow registers</title>
+ <programlisting>
+u8 (*sff_check_status)(struct ata_port *ap);
+u8 (*sff_check_altstatus)(struct ata_port *ap);
+ </programlisting>
+
+ <para>
+ Reads the Status/AltStatus ATA shadow register from
+ hardware. On some hardware, reading the Status register has
+ the side effect of clearing the interrupt condition.
+ Most drivers for taskfile-based hardware use
+ ata_sff_check_status() for this hook.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Write specific ATA shadow register</title>
+ <programlisting>
+void (*sff_set_devctl)(struct ata_port *ap, u8 ctl);
+ </programlisting>
+
+ <para>
+ Write the device control ATA shadow register to the hardware.
+ Most drivers don't need to define this.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Select ATA device on bus</title>
+ <programlisting>
+void (*sff_dev_select)(struct ata_port *ap, unsigned int device);
+ </programlisting>
+
+ <para>
+ Issues the low-level hardware command(s) that causes one of N
+ hardware devices to be considered 'selected' (active and
+ available for use) on the ATA bus. This generally has no
+ meaning on FIS-based devices.
+ </para>
+ <para>
+ Most drivers for taskfile-based hardware use
+ ata_sff_dev_select() for this hook.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Private tuning method</title>
+ <programlisting>
+void (*set_mode) (struct ata_port *ap);
+ </programlisting>
+
+ <para>
+ By default libata performs drive and controller tuning in
+ accordance with the ATA timing rules and also applies blacklists
+ and cable limits. Some controllers need special handling and have
+ custom tuning rules, typically raid controllers that use ATA
+ commands but do not actually do drive timing.
+ </para>
+
+ <warning>
+ <para>
+ This hook should not be used to replace the standard controller
+ tuning logic when a controller has quirks. Replacing the default
+ tuning logic in that case would bypass handling for drive and
+ bridge quirks that may be important to data reliability. If a
+ controller needs to filter the mode selection it should use the
+ mode_filter hook instead.
+ </para>
+ </warning>
+
+ </sect2>
+
+ <sect2><title>Control PCI IDE BMDMA engine</title>
+ <programlisting>
+void (*bmdma_setup) (struct ata_queued_cmd *qc);
+void (*bmdma_start) (struct ata_queued_cmd *qc);
+void (*bmdma_stop) (struct ata_port *ap);
+u8 (*bmdma_status) (struct ata_port *ap);
+ </programlisting>
+
+ <para>
+When setting up an IDE BMDMA transaction, these hooks arm
+(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
+the hardware's DMA engine. ->bmdma_status is used to read the standard
+PCI IDE DMA Status register.
+ </para>
+
+ <para>
+These hooks are typically either no-ops, or simply not implemented, in
+FIS-based drivers.
+ </para>
+ <para>
+Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
+hook. ata_bmdma_setup() will write the pointer to the PRD table to
+the IDE PRD Table Address register, enable DMA in the DMA Command
+register, and call exec_command() to begin the transfer.
+ </para>
+ <para>
+Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
+hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
+Command register.
+ </para>
+ <para>
+Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
+hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
+command register.
+ </para>
+ <para>
+Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
+ </para>
+
+ </sect2>
+
+ <sect2><title>High-level taskfile hooks</title>
+ <programlisting>
+void (*qc_prep) (struct ata_queued_cmd *qc);
+int (*qc_issue) (struct ata_queued_cmd *qc);
+ </programlisting>
+
+ <para>
+ Higher-level hooks, these two hooks can potentially supercede
+ several of the above taskfile/DMA engine hooks. ->qc_prep is
+ called after the buffers have been DMA-mapped, and is typically
+ used to populate the hardware's DMA scatter-gather table.
+ Most drivers use the standard ata_qc_prep() helper function, but
+ more advanced drivers roll their own.
+ </para>
+ <para>
+ ->qc_issue is used to make a command active, once the hardware
+ and S/G tables have been prepared. IDE BMDMA drivers use the
+ helper function ata_qc_issue_prot() for taskfile protocol-based
+ dispatch. More advanced drivers implement their own ->qc_issue.
+ </para>
+ <para>
+ ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
+ ->bmdma_start() as necessary to initiate a transfer.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Exception and probe handling (EH)</title>
+ <programlisting>
+void (*eng_timeout) (struct ata_port *ap);
+void (*phy_reset) (struct ata_port *ap);
+ </programlisting>
+
+ <para>
+Deprecated. Use ->error_handler() instead.
+ </para>
+
+ <programlisting>
+void (*freeze) (struct ata_port *ap);
+void (*thaw) (struct ata_port *ap);
+ </programlisting>
+
+ <para>
+ata_port_freeze() is called when HSM violations or some other
+condition disrupts normal operation of the port. A frozen port
+is not allowed to perform any operation until the port is
+thawed, which usually follows a successful reset.
+ </para>
+
+ <para>
+The optional ->freeze() callback can be used for freezing the port
+hardware-wise (e.g. mask interrupt and stop DMA engine). If a
+port cannot be frozen hardware-wise, the interrupt handler
+must ack and clear interrupts unconditionally while the port
+is frozen.
+ </para>
+ <para>
+The optional ->thaw() callback is called to perform the opposite of ->freeze():
+prepare the port for normal operation once again. Unmask interrupts,
+start DMA engine, etc.
+ </para>
+
+ <programlisting>
+void (*error_handler) (struct ata_port *ap);
+ </programlisting>
+
+ <para>
+->error_handler() is a driver's hook into probe, hotplug, and recovery
+and other exceptional conditions. The primary responsibility of an
+implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set
+of EH hooks as arguments:
+ </para>
+
+ <para>
+'prereset' hook (may be NULL) is called during an EH reset, before any other actions
+are taken.
+ </para>
+
+ <para>
+'postreset' hook (may be NULL) is called after the EH reset is performed. Based on
+existing conditions, severity of the problem, and hardware capabilities,
+ </para>
+
+ <para>
+Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be
+called to perform the low-level EH reset.
+ </para>
+
+ <programlisting>
+void (*post_internal_cmd) (struct ata_queued_cmd *qc);
+ </programlisting>
+
+ <para>
+Perform any hardware-specific actions necessary to finish processing
+after executing a probe-time or EH-time command via ata_exec_internal().
+ </para>
+
+ </sect2>
+
+ <sect2><title>Hardware interrupt handling</title>
+ <programlisting>
+irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
+void (*irq_clear) (struct ata_port *);
+ </programlisting>
+
+ <para>
+ ->irq_handler is the interrupt handling routine registered with
+ the system, by libata. ->irq_clear is called during probe just
+ before the interrupt handler is registered, to be sure hardware
+ is quiet.
+ </para>
+ <para>
+ The second argument, dev_instance, should be cast to a pointer
+ to struct ata_host_set.
+ </para>
+ <para>
+ Most legacy IDE drivers use ata_sff_interrupt() for the
+ irq_handler hook, which scans all ports in the host_set,
+ determines which queued command was active (if any), and calls
+ ata_sff_host_intr(ap,qc).
+ </para>
+ <para>
+ Most legacy IDE drivers use ata_sff_irq_clear() for the
+ irq_clear() hook, which simply clears the interrupt and error
+ flags in the DMA status register.
+ </para>
+
+ </sect2>
+
+ <sect2><title>SATA phy read/write</title>
+ <programlisting>
+int (*scr_read) (struct ata_port *ap, unsigned int sc_reg,
+ u32 *val);
+int (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
+ u32 val);
+ </programlisting>
+
+ <para>
+ Read and write standard SATA phy registers. Currently only used
+ if ->phy_reset hook called the sata_phy_reset() helper function.
+ sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
+ </para>
+
+ </sect2>
+
+ <sect2><title>Init and shutdown</title>
+ <programlisting>
+int (*port_start) (struct ata_port *ap);
+void (*port_stop) (struct ata_port *ap);
+void (*host_stop) (struct ata_host_set *host_set);
+ </programlisting>
+
+ <para>
+ ->port_start() is called just after the data structures for each
+ port are initialized. Typically this is used to alloc per-port
+ DMA buffers / tables / rings, enable DMA engines, and similar
+ tasks. Some drivers also use this entry point as a chance to
+ allocate driver-private memory for ap->private_data.
+ </para>
+ <para>
+ Many drivers use ata_port_start() as this hook or call
+ it from their own port_start() hooks. ata_port_start()
+ allocates space for a legacy IDE PRD table and returns.
+ </para>
+ <para>
+ ->port_stop() is called after ->host_stop(). Its sole function
+ is to release DMA/memory resources, now that they are no longer
+ actively being used. Many drivers also free driver-private
+ data from port at this time.
+ </para>
+ <para>
+ ->host_stop() is called after all ->port_stop() calls
+have completed. The hook must finalize hardware shutdown, release DMA
+and other resources, etc.
+ This hook may be specified as NULL, in which case it is not called.
+ </para>
+
+ </sect2>
+
+ </sect1>
+ </chapter>
+
+ <chapter id="libataEH">
+ <title>Error handling</title>
+
+ <para>
+ This chapter describes how errors are handled under libata.
+ Readers are advised to read SCSI EH
+ (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first.
+ </para>
+
+ <sect1><title>Origins of commands</title>
+ <para>
+ In libata, a command is represented with struct ata_queued_cmd
+ or qc. qc's are preallocated during port initialization and
+ repetitively used for command executions. Currently only one
+ qc is allocated per port but yet-to-be-merged NCQ branch
+ allocates one for each tag and maps each qc to NCQ tag 1-to-1.
+ </para>
+ <para>
+ libata commands can originate from two sources - libata itself
+ and SCSI midlayer. libata internal commands are used for
+ initialization and error handling. All normal blk requests
+ and commands for SCSI emulation are passed as SCSI commands
+ through queuecommand callback of SCSI host template.
+ </para>
+ </sect1>
+
+ <sect1><title>How commands are issued</title>
+
+ <variablelist>
+
+ <varlistentry><term>Internal commands</term>
+ <listitem>
+ <para>
+ First, qc is allocated and initialized using
+ ata_qc_new_init(). Although ata_qc_new_init() doesn't
+ implement any wait or retry mechanism when qc is not
+ available, internal commands are currently issued only during
+ initialization and error recovery, so no other command is
+ active and allocation is guaranteed to succeed.
+ </para>
+ <para>
+ Once allocated qc's taskfile is initialized for the command to
+ be executed. qc currently has two mechanisms to notify
+ completion. One is via qc->complete_fn() callback and the
+ other is completion qc->waiting. qc->complete_fn() callback
+ is the asynchronous path used by normal SCSI translated
+ commands and qc->waiting is the synchronous (issuer sleeps in
+ process context) path used by internal commands.
+ </para>
+ <para>
+ Once initialization is complete, host_set lock is acquired
+ and the qc is issued.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>SCSI commands</term>
+ <listitem>
+ <para>
+ All libata drivers use ata_scsi_queuecmd() as
+ hostt->queuecommand callback. scmds can either be simulated
+ or translated. No qc is involved in processing a simulated
+ scmd. The result is computed right away and the scmd is
+ completed.
+ </para>
+ <para>
+ For a translated scmd, ata_qc_new_init() is invoked to
+ allocate a qc and the scmd is translated into the qc. SCSI
+ midlayer's completion notification function pointer is stored
+ into qc->scsidone.
+ </para>
+ <para>
+ qc->complete_fn() callback is used for completion
+ notification. ATA commands use ata_scsi_qc_complete() while
+ ATAPI commands use atapi_qc_complete(). Both functions end up
+ calling qc->scsidone to notify upper layer when the qc is
+ finished. After translation is completed, the qc is issued
+ with ata_qc_issue().
+ </para>
+ <para>
+ Note that SCSI midlayer invokes hostt->queuecommand while
+ holding host_set lock, so all above occur while holding
+ host_set lock.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+ </sect1>
+
+ <sect1><title>How commands are processed</title>
+ <para>
+ Depending on which protocol and which controller are used,
+ commands are processed differently. For the purpose of
+ discussion, a controller which uses taskfile interface and all
+ standard callbacks is assumed.
+ </para>
+ <para>
+ Currently 6 ATA command protocols are used. They can be
+ sorted into the following four categories according to how
+ they are processed.
+ </para>
+
+ <variablelist>
+ <varlistentry><term>ATA NO DATA or DMA</term>
+ <listitem>
+ <para>
+ ATA_PROT_NODATA and ATA_PROT_DMA fall into this category.
+ These types of commands don't require any software
+ intervention once issued. Device will raise interrupt on
+ completion.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>ATA PIO</term>
+ <listitem>
+ <para>
+ ATA_PROT_PIO is in this category. libata currently
+ implements PIO with polling. ATA_NIEN bit is set to turn
+ off interrupt and pio_task on ata_wq performs polling and
+ IO.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>ATAPI NODATA or DMA</term>
+ <listitem>
+ <para>
+ ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this
+ category. packet_task is used to poll BSY bit after
+ issuing PACKET command. Once BSY is turned off by the
+ device, packet_task transfers CDB and hands off processing
+ to interrupt handler.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>ATAPI PIO</term>
+ <listitem>
+ <para>
+ ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set
+ and, as in ATAPI NODATA or DMA, packet_task submits cdb.
+ However, after submitting cdb, further processing (data
+ transfer) is handed off to pio_task.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </sect1>
+
+ <sect1><title>How commands are completed</title>
+ <para>
+ Once issued, all qc's are either completed with
+ ata_qc_complete() or time out. For commands which are handled
+ by interrupts, ata_host_intr() invokes ata_qc_complete(), and,
+ for PIO tasks, pio_task invokes ata_qc_complete(). In error
+ cases, packet_task may also complete commands.
+ </para>
+ <para>
+ ata_qc_complete() does the following.
+ </para>
+
+ <orderedlist>
+
+ <listitem>
+ <para>
+ DMA memory is unmapped.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ ATA_QCFLAG_ACTIVE is clared from qc->flags.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ qc->complete_fn() callback is invoked. If the return value of
+ the callback is not zero. Completion is short circuited and
+ ata_qc_complete() returns.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ __ata_qc_complete() is called, which does
+ <orderedlist>
+
+ <listitem>
+ <para>
+ qc->flags is cleared to zero.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ ap->active_tag and qc->tag are poisoned.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ qc->waiting is claread &amp; completed (in that order).
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ qc is deallocated by clearing appropriate bit in ap->qactive.
+ </para>
+ </listitem>
+
+ </orderedlist>
+ </para>
+ </listitem>
+
+ </orderedlist>
+
+ <para>
+ So, it basically notifies upper layer and deallocates qc. One
+ exception is short-circuit path in #3 which is used by
+ atapi_qc_complete().
+ </para>
+ <para>
+ For all non-ATAPI commands, whether it fails or not, almost
+ the same code path is taken and very little error handling
+ takes place. A qc is completed with success status if it
+ succeeded, with failed status otherwise.
+ </para>
+ <para>
+ However, failed ATAPI commands require more handling as
+ REQUEST SENSE is needed to acquire sense data. If an ATAPI
+ command fails, ata_qc_complete() is invoked with error status,
+ which in turn invokes atapi_qc_complete() via
+ qc->complete_fn() callback.
+ </para>
+ <para>
+ This makes atapi_qc_complete() set scmd->result to
+ SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As
+ the sense data is empty but scmd->result is CHECK CONDITION,
+ SCSI midlayer will invoke EH for the scmd, and returning 1
+ makes ata_qc_complete() to return without deallocating the qc.
+ This leads us to ata_scsi_error() with partially completed qc.
+ </para>
+
+ </sect1>
+
+ <sect1><title>ata_scsi_error()</title>
+ <para>
+ ata_scsi_error() is the current transportt->eh_strategy_handler()
+ for libata. As discussed above, this will be entered in two
+ cases - timeout and ATAPI error completion. This function
+ calls low level libata driver's eng_timeout() callback, the
+ standard callback for which is ata_eng_timeout(). It checks
+ if a qc is active and calls ata_qc_timeout() on the qc if so.
+ Actual error handling occurs in ata_qc_timeout().
+ </para>
+ <para>
+ If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and
+ completes the qc. Note that as we're currently in EH, we
+ cannot call scsi_done. As described in SCSI EH doc, a
+ recovered scmd should be either retried with
+ scsi_queue_insert() or finished with scsi_finish_command().
+ Here, we override qc->scsidone with scsi_finish_command() and
+ calls ata_qc_complete().
+ </para>
+ <para>
+ If EH is invoked due to a failed ATAPI qc, the qc here is
+ completed but not deallocated. The purpose of this
+ half-completion is to use the qc as place holder to make EH
+ code reach this place. This is a bit hackish, but it works.
+ </para>
+ <para>
+ Once control reaches here, the qc is deallocated by invoking
+ __ata_qc_complete() explicitly. Then, internal qc for REQUEST
+ SENSE is issued. Once sense data is acquired, scmd is
+ finished by directly invoking scsi_finish_command() on the
+ scmd. Note that as we already have completed and deallocated
+ the qc which was associated with the scmd, we don't need
+ to/cannot call ata_qc_complete() again.
+ </para>
+
+ </sect1>
+
+ <sect1><title>Problems with the current EH</title>
+
+ <itemizedlist>
+
+ <listitem>
+ <para>
+ Error representation is too crude. Currently any and all
+ error conditions are represented with ATA STATUS and ERROR
+ registers. Errors which aren't ATA device errors are treated
+ as ATA device errors by setting ATA_ERR bit. Better error
+ descriptor which can properly represent ATA and other
+ errors/exceptions is needed.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ When handling timeouts, no action is taken to make device
+ forget about the timed out command and ready for new commands.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ EH handling via ata_scsi_error() is not properly protected
+ from usual command processing. On EH entrance, the device is
+ not in quiescent state. Timed out commands may succeed or
+ fail any time. pio_task and atapi_task may still be running.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Too weak error recovery. Devices / controllers causing HSM
+ mismatch errors and other errors quite often require reset to
+ return to known state. Also, advanced error handling is
+ necessary to support features like NCQ and hotplug.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ ATA errors are directly handled in the interrupt handler and
+ PIO errors in pio_task. This is problematic for advanced
+ error handling for the following reasons.
+ </para>
+ <para>
+ First, advanced error handling often requires context and
+ internal qc execution.
+ </para>
+ <para>
+ Second, even a simple failure (say, CRC error) needs
+ information gathering and could trigger complex error handling
+ (say, resetting &amp; reconfiguring). Having multiple code
+ paths to gather information, enter EH and trigger actions
+ makes life painful.
+ </para>
+ <para>
+ Third, scattered EH code makes implementing low level drivers
+ difficult. Low level drivers override libata callbacks. If
+ EH is scattered over several places, each affected callbacks
+ should perform its part of error handling. This can be error
+ prone and painful.
+ </para>
+ </listitem>
+
+ </itemizedlist>
+ </sect1>
+ </chapter>
+
+ <chapter id="libataExt">
+ <title>libata Library</title>
+!Edrivers/ata/libata-core.c
+ </chapter>
+
+ <chapter id="libataInt">
+ <title>libata Core Internals</title>
+!Idrivers/ata/libata-core.c
+ </chapter>
+
+ <chapter id="libataScsiInt">
+ <title>libata SCSI translation/emulation</title>
+!Edrivers/ata/libata-scsi.c
+!Idrivers/ata/libata-scsi.c
+ </chapter>
+
+ <chapter id="ataExceptions">
+ <title>ATA errors and exceptions</title>
+
+ <para>
+ This chapter tries to identify what error/exception conditions exist
+ for ATA/ATAPI devices and describe how they should be handled in
+ implementation-neutral way.
+ </para>
+
+ <para>
+ The term 'error' is used to describe conditions where either an
+ explicit error condition is reported from device or a command has
+ timed out.
+ </para>
+
+ <para>
+ The term 'exception' is either used to describe exceptional
+ conditions which are not errors (say, power or hotplug events), or
+ to describe both errors and non-error exceptional conditions. Where
+ explicit distinction between error and exception is necessary, the
+ term 'non-error exception' is used.
+ </para>
+
+ <sect1 id="excat">
+ <title>Exception categories</title>
+ <para>
+ Exceptions are described primarily with respect to legacy
+ taskfile + bus master IDE interface. If a controller provides
+ other better mechanism for error reporting, mapping those into
+ categories described below shouldn't be difficult.
+ </para>
+
+ <para>
+ In the following sections, two recovery actions - reset and
+ reconfiguring transport - are mentioned. These are described
+ further in <xref linkend="exrec"/>.
+ </para>
+
+ <sect2 id="excatHSMviolation">
+ <title>HSM violation</title>
+ <para>
+ This error is indicated when STATUS value doesn't match HSM
+ requirement during issuing or execution any ATA/ATAPI command.
+ </para>
+
+ <itemizedlist>
+ <title>Examples</title>
+
+ <listitem>
+ <para>
+ ATA_STATUS doesn't contain !BSY &amp;&amp; DRDY &amp;&amp; !DRQ while trying
+ to issue a command.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ !BSY &amp;&amp; !DRQ during PIO data transfer.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ DRQ on command completion.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ !BSY &amp;&amp; ERR after CDB transfer starts but before the
+ last byte of CDB is transferred. ATA/ATAPI standard states
+ that &quot;The device shall not terminate the PACKET command
+ with an error before the last byte of the command packet has
+ been written&quot; in the error outputs description of PACKET
+ command and the state diagram doesn't include such
+ transitions.
+ </para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para>
+ In these cases, HSM is violated and not much information
+ regarding the error can be acquired from STATUS or ERROR
+ register. IOW, this error can be anything - driver bug,
+ faulty device, controller and/or cable.
+ </para>
+
+ <para>
+ As HSM is violated, reset is necessary to restore known state.
+ Reconfiguring transport for lower speed might be helpful too
+ as transmission errors sometimes cause this kind of errors.
+ </para>
+ </sect2>
+
+ <sect2 id="excatDevErr">
+ <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title>
+
+ <para>
+ These are errors detected and reported by ATA/ATAPI devices
+ indicating device problems. For this type of errors, STATUS
+ and ERROR register values are valid and describe error
+ condition. Note that some of ATA bus errors are detected by
+ ATA/ATAPI devices and reported using the same mechanism as
+ device errors. Those cases are described later in this
+ section.
+ </para>
+
+ <para>
+ For ATA commands, this type of errors are indicated by !BSY
+ &amp;&amp; ERR during command execution and on completion.
+ </para>
+
+ <para>For ATAPI commands,</para>
+
+ <itemizedlist>
+
+ <listitem>
+ <para>
+ !BSY &amp;&amp; ERR &amp;&amp; ABRT right after issuing PACKET
+ indicates that PACKET command is not supported and falls in
+ this category.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ !BSY &amp;&amp; ERR(==CHK) &amp;&amp; !ABRT after the last
+ byte of CDB is transferred indicates CHECK CONDITION and
+ doesn't fall in this category.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ !BSY &amp;&amp; ERR(==CHK) &amp;&amp; ABRT after the last byte
+ of CDB is transferred *probably* indicates CHECK CONDITION and
+ doesn't fall in this category.
+ </para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para>
+ Of errors detected as above, the followings are not ATA/ATAPI
+ device errors but ATA bus errors and should be handled
+ according to <xref linkend="excatATAbusErr"/>.
+ </para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term>CRC error during data transfer</term>
+ <listitem>
+ <para>
+ This is indicated by ICRC bit in the ERROR register and
+ means that corruption occurred during data transfer. Up to
+ ATA/ATAPI-7, the standard specifies that this bit is only
+ applicable to UDMA transfers but ATA/ATAPI-8 draft revision
+ 1f says that the bit may be applicable to multiword DMA and
+ PIO.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>ABRT error during data transfer or on completion</term>
+ <listitem>
+ <para>
+ Up to ATA/ATAPI-7, the standard specifies that ABRT could be
+ set on ICRC errors and on cases where a device is not able
+ to complete a command. Combined with the fact that MWDMA
+ and PIO transfer errors aren't allowed to use ICRC bit up to
+ ATA/ATAPI-7, it seems to imply that ABRT bit alone could
+ indicate transfer errors.
+ </para>
+ <para>
+ However, ATA/ATAPI-8 draft revision 1f removes the part
+ that ICRC errors can turn on ABRT. So, this is kind of
+ gray area. Some heuristics are needed here.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>
+ ATA/ATAPI device errors can be further categorized as follows.
+ </para>
+
+ <variablelist>
+
+ <varlistentry>
+ <term>Media errors</term>
+ <listitem>
+ <para>
+ This is indicated by UNC bit in the ERROR register. ATA
+ devices reports UNC error only after certain number of
+ retries cannot recover the data, so there's nothing much
+ else to do other than notifying upper layer.
+ </para>
+ <para>
+ READ and WRITE commands report CHS or LBA of the first
+ failed sector but ATA/ATAPI standard specifies that the
+ amount of transferred data on error completion is
+ indeterminate, so we cannot assume that sectors preceding
+ the failed sector have been transferred and thus cannot
+ complete those sectors successfully as SCSI does.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>Media changed / media change requested error</term>
+ <listitem>
+ <para>
+ &lt;&lt;TODO: fill here&gt;&gt;
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>Address error</term>
+ <listitem>
+ <para>
+ This is indicated by IDNF bit in the ERROR register.
+ Report to upper layer.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>Other errors</term>
+ <listitem>
+ <para>
+ This can be invalid command or parameter indicated by ABRT
+ ERROR bit or some other error condition. Note that ABRT
+ bit can indicate a lot of things including ICRC and Address
+ errors. Heuristics needed.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>
+ Depending on commands, not all STATUS/ERROR bits are
+ applicable. These non-applicable bits are marked with
+ &quot;na&quot; in the output descriptions but up to ATA/ATAPI-7
+ no definition of &quot;na&quot; can be found. However,
+ ATA/ATAPI-8 draft revision 1f describes &quot;N/A&quot; as
+ follows.
+ </para>
+
+ <blockquote>
+ <variablelist>
+ <varlistentry><term>3.2.3.3a N/A</term>
+ <listitem>
+ <para>
+ A keyword the indicates a field has no defined value in
+ this standard and should not be checked by the host or
+ device. N/A fields should be cleared to zero.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </blockquote>
+
+ <para>
+ So, it seems reasonable to assume that &quot;na&quot; bits are
+ cleared to zero by devices and thus need no explicit masking.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatATAPIcc">
+ <title>ATAPI device CHECK CONDITION</title>
+
+ <para>
+ ATAPI device CHECK CONDITION error is indicated by set CHK bit
+ (ERR bit) in the STATUS register after the last byte of CDB is
+ transferred for a PACKET command. For this kind of errors,
+ sense data should be acquired to gather information regarding
+ the errors. REQUEST SENSE packet command should be used to
+ acquire sense data.
+ </para>
+
+ <para>
+ Once sense data is acquired, this type of errors can be
+ handled similary to other SCSI errors. Note that sense data
+ may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR
+ &amp;&amp; ASC/ASCQ 47h/00h SCSI PARITY ERROR). In such
+ cases, the error should be considered as an ATA bus error and
+ handled according to <xref linkend="excatATAbusErr"/>.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatNCQerr">
+ <title>ATA device error (NCQ)</title>
+
+ <para>
+ NCQ command error is indicated by cleared BSY and set ERR bit
+ during NCQ command phase (one or more NCQ commands
+ outstanding). Although STATUS and ERROR registers will
+ contain valid values describing the error, READ LOG EXT is
+ required to clear the error condition, determine which command
+ has failed and acquire more information.
+ </para>
+
+ <para>
+ READ LOG EXT Log Page 10h reports which tag has failed and
+ taskfile register values describing the error. With this
+ information the failed command can be handled as a normal ATA
+ command error as in <xref linkend="excatDevErr"/> and all
+ other in-flight commands must be retried. Note that this
+ retry should not be counted - it's likely that commands
+ retried this way would have completed normally if it were not
+ for the failed command.
+ </para>
+
+ <para>
+ Note that ATA bus errors can be reported as ATA device NCQ
+ errors. This should be handled as described in <xref
+ linkend="excatATAbusErr"/>.
+ </para>
+
+ <para>
+ If READ LOG EXT Log Page 10h fails or reports NQ, we're
+ thoroughly screwed. This condition should be treated
+ according to <xref linkend="excatHSMviolation"/>.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatATAbusErr">
+ <title>ATA bus error</title>
+
+ <para>
+ ATA bus error means that data corruption occurred during
+ transmission over ATA bus (SATA or PATA). This type of errors
+ can be indicated by
+ </para>
+
+ <itemizedlist>
+
+ <listitem>
+ <para>
+ ICRC or ABRT error as described in <xref linkend="excatDevErr"/>.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Controller-specific error completion with error information
+ indicating transmission error.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ On some controllers, command timeout. In this case, there may
+ be a mechanism to determine that the timeout is due to
+ transmission error.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Unknown/random errors, timeouts and all sorts of weirdities.
+ </para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para>
+ As described above, transmission errors can cause wide variety
+ of symptoms ranging from device ICRC error to random device
+ lockup, and, for many cases, there is no way to tell if an
+ error condition is due to transmission error or not;
+ therefore, it's necessary to employ some kind of heuristic
+ when dealing with errors and timeouts. For example,
+ encountering repetitive ABRT errors for known supported
+ command is likely to indicate ATA bus error.
+ </para>
+
+ <para>
+ Once it's determined that ATA bus errors have possibly
+ occurred, lowering ATA bus transmission speed is one of
+ actions which may alleviate the problem. See <xref
+ linkend="exrecReconf"/> for more information.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatPCIbusErr">
+ <title>PCI bus error</title>
+
+ <para>
+ Data corruption or other failures during transmission over PCI
+ (or other system bus). For standard BMDMA, this is indicated
+ by Error bit in the BMDMA Status register. This type of
+ errors must be logged as it indicates something is very wrong
+ with the system. Resetting host controller is recommended.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatLateCompletion">
+ <title>Late completion</title>
+
+ <para>
+ This occurs when timeout occurs and the timeout handler finds
+ out that the timed out command has completed successfully or
+ with error. This is usually caused by lost interrupts. This
+ type of errors must be logged. Resetting host controller is
+ recommended.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatUnknown">
+ <title>Unknown error (timeout)</title>
+
+ <para>
+ This is when timeout occurs and the command is still
+ processing or the host and device are in unknown state. When
+ this occurs, HSM could be in any valid or invalid state. To
+ bring the device to known state and make it forget about the
+ timed out command, resetting is necessary. The timed out
+ command may be retried.
+ </para>
+
+ <para>
+ Timeouts can also be caused by transmission errors. Refer to
+ <xref linkend="excatATAbusErr"/> for more details.
+ </para>
+
+ </sect2>
+
+ <sect2 id="excatHoplugPM">
+ <title>Hotplug and power management exceptions</title>
+
+ <para>
+ &lt;&lt;TODO: fill here&gt;&gt;
+ </para>
+
+ </sect2>
+
+ </sect1>
+
+ <sect1 id="exrec">
+ <title>EH recovery actions</title>
+
+ <para>
+ This section discusses several important recovery actions.
+ </para>
+
+ <sect2 id="exrecClr">
+ <title>Clearing error condition</title>
+
+ <para>
+ Many controllers require its error registers to be cleared by
+ error handler. Different controllers may have different
+ requirements.
+ </para>
+
+ <para>
+ For SATA, it's strongly recommended to clear at least SError
+ register during error handling.
+ </para>
+ </sect2>
+
+ <sect2 id="exrecRst">
+ <title>Reset</title>
+
+ <para>
+ During EH, resetting is necessary in the following cases.
+ </para>
+
+ <itemizedlist>
+
+ <listitem>
+ <para>
+ HSM is in unknown or invalid state
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ HBA is in unknown or invalid state
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ EH needs to make HBA/device forget about in-flight commands
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ HBA/device behaves weirdly
+ </para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para>
+ Resetting during EH might be a good idea regardless of error
+ condition to improve EH robustness. Whether to reset both or
+ either one of HBA and device depends on situation but the
+ following scheme is recommended.
+ </para>
+
+ <itemizedlist>
+
+ <listitem>
+ <para>
+ When it's known that HBA is in ready state but ATA/ATAPI
+ device is in unknown state, reset only device.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ If HBA is in unknown state, reset both HBA and device.
+ </para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para>
+ HBA resetting is implementation specific. For a controller
+ complying to taskfile/BMDMA PCI IDE, stopping active DMA
+ transaction may be sufficient iff BMDMA state is the only HBA
+ context. But even mostly taskfile/BMDMA PCI IDE complying
+ controllers may have implementation specific requirements and
+ mechanism to reset themselves. This must be addressed by
+ specific drivers.
+ </para>
+
+ <para>
+ OTOH, ATA/ATAPI standard describes in detail ways to reset
+ ATA/ATAPI devices.
+ </para>
+
+ <variablelist>
+
+ <varlistentry><term>PATA hardware reset</term>
+ <listitem>
+ <para>
+ This is hardware initiated device reset signalled with
+ asserted PATA RESET- signal. There is no standard way to
+ initiate hardware reset from software although some
+ hardware provides registers that allow driver to directly
+ tweak the RESET- signal.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>Software reset</term>
+ <listitem>
+ <para>
+ This is achieved by turning CONTROL SRST bit on for at
+ least 5us. Both PATA and SATA support it but, in case of
+ SATA, this may require controller-specific support as the
+ second Register FIS to clear SRST should be transmitted
+ while BSY bit is still set. Note that on PATA, this resets
+ both master and slave devices on a channel.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term>
+ <listitem>
+ <para>
+ Although ATA/ATAPI standard doesn't describe exactly, EDD
+ implies some level of resetting, possibly similar level
+ with software reset. Host-side EDD protocol can be handled
+ with normal command processing and most SATA controllers
+ should be able to handle EDD's just like other commands.
+ As in software reset, EDD affects both devices on a PATA
+ bus.
+ </para>
+ <para>
+ Although EDD does reset devices, this doesn't suit error
+ handling as EDD cannot be issued while BSY is set and it's
+ unclear how it will act when device is in unknown/weird
+ state.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>ATAPI DEVICE RESET command</term>
+ <listitem>
+ <para>
+ This is very similar to software reset except that reset
+ can be restricted to the selected device without affecting
+ the other device sharing the cable.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry><term>SATA phy reset</term>
+ <listitem>
+ <para>
+ This is the preferred way of resetting a SATA device. In
+ effect, it's identical to PATA hardware reset. Note that
+ this can be done with the standard SCR Control register.
+ As such, it's usually easier to implement than software
+ reset.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ </variablelist>
+
+ <para>
+ One more thing to consider when resetting devices is that
+ resetting clears certain configuration parameters and they
+ need to be set to their previous or newly adjusted values
+ after reset.
+ </para>
+
+ <para>
+ Parameters affected are.
+ </para>
+
+ <itemizedlist>
+
+ <listitem>
+ <para>
+ CHS set up with INITIALIZE DEVICE PARAMETERS (seldom used)
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Parameters set with SET FEATURES including transfer mode setting
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Block count set with SET MULTIPLE MODE
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Other parameters (SET MAX, MEDIA LOCK...)
+ </para>
+ </listitem>
+
+ </itemizedlist>
+
+ <para>
+ ATA/ATAPI standard specifies that some parameters must be
+ maintained across hardware or software reset, but doesn't
+ strictly specify all of them. Always reconfiguring needed
+ parameters after reset is required for robustness. Note that
+ this also applies when resuming from deep sleep (power-off).
+ </para>
+
+ <para>
+ Also, ATA/ATAPI standard requires that IDENTIFY DEVICE /
+ IDENTIFY PACKET DEVICE is issued after any configuration
+ parameter is updated or a hardware reset and the result used
+ for further operation. OS driver is required to implement
+ revalidation mechanism to support this.
+ </para>
+
+ </sect2>
+
+ <sect2 id="exrecReconf">
+ <title>Reconfigure transport</title>
+
+ <para>
+ For both PATA and SATA, a lot of corners are cut for cheap
+ connectors, cables or controllers and it's quite common to see
+ high transmission error rate. This can be mitigated by
+ lowering transmission speed.
+ </para>
+
+ <para>
+ The following is a possible scheme Jeff Garzik suggested.
+ </para>
+
+ <blockquote>
+ <para>
+ If more than $N (3?) transmission errors happen in 15 minutes,
+ </para>
+ <itemizedlist>
+ <listitem>
+ <para>
+ if SATA, decrease SATA PHY speed. if speed cannot be decreased,
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ decrease UDMA xfer speed. if at UDMA0, switch to PIO4,
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ decrease PIO xfer speed. if at PIO3, complain, but continue
+ </para>
+ </listitem>
+ </itemizedlist>
+ </blockquote>
+
+ </sect2>
+
+ </sect1>
+
+ </chapter>
+
+ <chapter id="PiixInt">
+ <title>ata_piix Internals</title>
+!Idrivers/ata/ata_piix.c
+ </chapter>
+
+ <chapter id="SILInt">
+ <title>sata_sil Internals</title>
+!Idrivers/ata/sata_sil.c
+ </chapter>
+
+ <chapter id="libataThanks">
+ <title>Thanks</title>
+ <para>
+ The bulk of the ATA knowledge comes thanks to long conversations with
+ Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
+ and SCSI specifications.
+ </para>
+ <para>
+ Thanks to Alan Cox for pointing out similarities
+ between SATA and SCSI, and in general for motivation to hack on
+ libata.
+ </para>
+ <para>
+ libata's device detection
+ method, ata_pio_devchk, and in general all the early probing was
+ based on extensive study of Hale Landis's probe/reset code in his
+ ATADRVR driver (www.ata-atapi.com).
+ </para>
+ </chapter>
+
+</book>