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diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 2f767e30b59e..abe71345160b 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -9,7 +9,7 @@ DOCBOOKS := z8530book.xml \ networking.xml \ lsm.xml \ - libata.xml mtdnand.xml librs.xml rapidio.xml \ + mtdnand.xml librs.xml rapidio.xml \ s390-drivers.xml scsi.xml \ sh.xml w1.xml diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl deleted file mode 100644 index 0320910b866d..000000000000 --- a/Documentation/DocBook/libata.tmpl +++ /dev/null @@ -1,1625 +0,0 @@ -<?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<->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 cleared 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 cleared & 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 & 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 && DRDY && !DRQ while trying - to issue a command. - </para> - </listitem> - - <listitem> - <para> - !BSY && !DRQ during PIO data transfer. - </para> - </listitem> - - <listitem> - <para> - DRQ on command completion. - </para> - </listitem> - - <listitem> - <para> - !BSY && ERR after CDB transfer starts but before the - last byte of CDB is transferred. ATA/ATAPI standard states - that "The device shall not terminate the PACKET command - with an error before the last byte of the command packet has - been written" 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 - && ERR during command execution and on completion. - </para> - - <para>For ATAPI commands,</para> - - <itemizedlist> - - <listitem> - <para> - !BSY && ERR && ABRT right after issuing PACKET - indicates that PACKET command is not supported and falls in - this category. - </para> - </listitem> - - <listitem> - <para> - !BSY && ERR(==CHK) && !ABRT after the last - byte of CDB is transferred indicates CHECK CONDITION and - doesn't fall in this category. - </para> - </listitem> - - <listitem> - <para> - !BSY && ERR(==CHK) && 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 following 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> - <<TODO: fill here>> - </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 - "na" in the output descriptions but up to ATA/ATAPI-7 - no definition of "na" can be found. However, - ATA/ATAPI-8 draft revision 1f describes "N/A" 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 "na" 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 similarly to other SCSI errors. Note that sense data - may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR - && 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> - <<TODO: fill here>> - </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> |