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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>