From 3b4bd47f8f4ed3aaf7c81c9b5d2d37ad79fadf4a Mon Sep 17 00:00:00 2001 From: Fathi Boudra Date: Sun, 28 Apr 2013 09:33:08 +0300 Subject: Imported Upstream version 3.9.0 --- Documentation/DocBook/libata.tmpl | 1625 +++++++++++++++++++++++++++++++++++++ 1 file changed, 1625 insertions(+) create mode 100644 Documentation/DocBook/libata.tmpl (limited to 'Documentation/DocBook/libata.tmpl') diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl new file mode 100644 index 00000000..deb71bae --- /dev/null +++ b/Documentation/DocBook/libata.tmpl @@ -0,0 +1,1625 @@ + + + + + + libATA Developer's Guide + + + + Jeff + Garzik + + + + + 2003-2006 + Jeff Garzik + + + + + The contents of this file are subject to the Open + Software License version 1.1 that can be found at + http://fedoraproject.org/wiki/Licensing:OSL1.1 + and is included herein by reference. + + + + 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. + + + + + + + + + Introduction + + 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. + + + This Guide documents the libATA driver API, library functions, library + internals, and a couple sample ATA low-level drivers. + + + + + libata Driver API + + 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. + + + 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. + + + struct ata_port_operations + + Disable ATA port + +void (*port_disable) (struct ata_port *); + + + + 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. + + + Called from ata_bus_probe() on a failed probe. + Called from ata_scsi_release(). + + + + + Post-IDENTIFY device configuration + +void (*dev_config) (struct ata_port *, struct ata_device *); + + + + 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. + + + This entry may be specified as NULL in ata_port_operations. + + + + + Set PIO/DMA mode + +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); + + + + 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. + + + 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. + + + ->post_set_mode() is + called unconditionally, after the SET FEATURES - XFER MODE + command completes successfully. + + + + ->set_piomode() is always called (if present), but + ->set_dma_mode() is only called if DMA is possible. + + + + + Taskfile read/write + +void (*sff_tf_load) (struct ata_port *ap, struct ata_taskfile *tf); +void (*sff_tf_read) (struct ata_port *ap, struct ata_taskfile *tf); + + + + ->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. + + + + + PIO data read/write + +void (*sff_data_xfer) (struct ata_device *, unsigned char *, unsigned int, int); + + + +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(). + + + + + ATA command execute + +void (*sff_exec_command)(struct ata_port *ap, struct ata_taskfile *tf); + + + + 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. + + + + + Per-cmd ATAPI DMA capabilities filter + +int (*check_atapi_dma) (struct ata_queued_cmd *qc); + + + +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. + + + This hook may be specified as NULL, in which case libata will + assume that atapi dma can be supported. + + + + + Read specific ATA shadow registers + +u8 (*sff_check_status)(struct ata_port *ap); +u8 (*sff_check_altstatus)(struct ata_port *ap); + + + + 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. + + + + + Write specific ATA shadow register + +void (*sff_set_devctl)(struct ata_port *ap, u8 ctl); + + + + Write the device control ATA shadow register to the hardware. + Most drivers don't need to define this. + + + + + Select ATA device on bus + +void (*sff_dev_select)(struct ata_port *ap, unsigned int device); + + + + 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. + + + Most drivers for taskfile-based hardware use + ata_sff_dev_select() for this hook. + + + + + Private tuning method + +void (*set_mode) (struct ata_port *ap); + + + + 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. + + + + + 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. + + + + + + Control PCI IDE BMDMA engine + +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); + + + +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. + + + +These hooks are typically either no-ops, or simply not implemented, in +FIS-based drivers. + + +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. + + +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. + + +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. + + +Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook. + + + + + High-level taskfile hooks + +void (*qc_prep) (struct ata_queued_cmd *qc); +int (*qc_issue) (struct ata_queued_cmd *qc); + + + + 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. + + + ->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. + + + ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and + ->bmdma_start() as necessary to initiate a transfer. + + + + + Exception and probe handling (EH) + +void (*eng_timeout) (struct ata_port *ap); +void (*phy_reset) (struct ata_port *ap); + + + +Deprecated. Use ->error_handler() instead. + + + +void (*freeze) (struct ata_port *ap); +void (*thaw) (struct ata_port *ap); + + + +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. + + + +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. + + +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. + + + +void (*error_handler) (struct ata_port *ap); + + + +->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: + + + +'prereset' hook (may be NULL) is called during an EH reset, before any other actions +are taken. + + + +'postreset' hook (may be NULL) is called after the EH reset is performed. Based on +existing conditions, severity of the problem, and hardware capabilities, + + + +Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be +called to perform the low-level EH reset. + + + +void (*post_internal_cmd) (struct ata_queued_cmd *qc); + + + +Perform any hardware-specific actions necessary to finish processing +after executing a probe-time or EH-time command via ata_exec_internal(). + + + + + Hardware interrupt handling + +irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); +void (*irq_clear) (struct ata_port *); + + + + ->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. + + + The second argument, dev_instance, should be cast to a pointer + to struct ata_host_set. + + + 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). + + + 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. + + + + + SATA phy read/write + +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); + + + + 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. + + + + + Init and shutdown + +int (*port_start) (struct ata_port *ap); +void (*port_stop) (struct ata_port *ap); +void (*host_stop) (struct ata_host_set *host_set); + + + + ->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. + + + 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. + + + ->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. + + + ->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. + + + + + + + + + Error handling + + + 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. + + + Origins of commands + + 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. + + + 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. + + + + How commands are issued + + + + Internal commands + + + 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. + + + 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. + + + Once initialization is complete, host_set lock is acquired + and the qc is issued. + + + + + SCSI commands + + + 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. + + + 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. + + + 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(). + + + Note that SCSI midlayer invokes hostt->queuecommand while + holding host_set lock, so all above occur while holding + host_set lock. + + + + + + + + How commands are processed + + 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. + + + Currently 6 ATA command protocols are used. They can be + sorted into the following four categories according to how + they are processed. + + + + ATA NO DATA or DMA + + + 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. + + + + + ATA PIO + + + 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. + + + + + ATAPI NODATA or DMA + + + 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. + + + + + ATAPI PIO + + + 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. + + + + + + + How commands are completed + + 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. + + + ata_qc_complete() does the following. + + + + + + + DMA memory is unmapped. + + + + + + ATA_QCFLAG_ACTIVE is clared from qc->flags. + + + + + + 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. + + + + + + __ata_qc_complete() is called, which does + + + + + qc->flags is cleared to zero. + + + + + + ap->active_tag and qc->tag are poisoned. + + + + + + qc->waiting is claread & completed (in that order). + + + + + + qc is deallocated by clearing appropriate bit in ap->qactive. + + + + + + + + + + + So, it basically notifies upper layer and deallocates qc. One + exception is short-circuit path in #3 which is used by + atapi_qc_complete(). + + + 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. + + + 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. + + + 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. + + + + + ata_scsi_error() + + 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(). + + + 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(). + + + 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. + + + 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. + + + + + Problems with the current EH + + + + + + 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. + + + + + + When handling timeouts, no action is taken to make device + forget about the timed out command and ready for new commands. + + + + + + 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. + + + + + + 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. + + + + + + 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. + + + First, advanced error handling often requires context and + internal qc execution. + + + 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. + + + 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. + + + + + + + + + libata Library +!Edrivers/ata/libata-core.c + + + + libata Core Internals +!Idrivers/ata/libata-core.c + + + + libata SCSI translation/emulation +!Edrivers/ata/libata-scsi.c +!Idrivers/ata/libata-scsi.c + + + + ATA errors and exceptions + + + 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. + + + + The term 'error' is used to describe conditions where either an + explicit error condition is reported from device or a command has + timed out. + + + + 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. + + + + Exception categories + + 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. + + + + In the following sections, two recovery actions - reset and + reconfiguring transport - are mentioned. These are described + further in . + + + + HSM violation + + This error is indicated when STATUS value doesn't match HSM + requirement during issuing or execution any ATA/ATAPI command. + + + + Examples + + + + ATA_STATUS doesn't contain !BSY && DRDY && !DRQ while trying + to issue a command. + + + + + + !BSY && !DRQ during PIO data transfer. + + + + + + DRQ on command completion. + + + + + + !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. + + + + + + + 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. + + + + 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. + + + + + ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION) + + + 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. + + + + For ATA commands, this type of errors are indicated by !BSY + && ERR during command execution and on completion. + + + For ATAPI commands, + + + + + + !BSY && ERR && ABRT right after issuing PACKET + indicates that PACKET command is not supported and falls in + this category. + + + + + + !BSY && ERR(==CHK) && !ABRT after the last + byte of CDB is transferred indicates CHECK CONDITION and + doesn't fall in this category. + + + + + + !BSY && ERR(==CHK) && ABRT after the last byte + of CDB is transferred *probably* indicates CHECK CONDITION and + doesn't fall in this category. + + + + + + + Of errors detected as above, the followings are not ATA/ATAPI + device errors but ATA bus errors and should be handled + according to . + + + + + + CRC error during data transfer + + + 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. + + + + + + ABRT error during data transfer or on completion + + + 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. + + + 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. + + + + + + + + ATA/ATAPI device errors can be further categorized as follows. + + + + + + Media errors + + + 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. + + + 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. + + + + + + Media changed / media change requested error + + + <<TODO: fill here>> + + + + + Address error + + + This is indicated by IDNF bit in the ERROR register. + Report to upper layer. + + + + + Other errors + + + 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. + + + + + + + + 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. + + +
+ + 3.2.3.3a N/A + + + 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. + + + + +
+ + + So, it seems reasonable to assume that "na" bits are + cleared to zero by devices and thus need no explicit masking. + + + + + + ATAPI device CHECK CONDITION + + + 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. + + + + 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 + && ASC/ASCQ 47h/00h SCSI PARITY ERROR). In such + cases, the error should be considered as an ATA bus error and + handled according to . + + + + + + ATA device error (NCQ) + + + 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. + + + + 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 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. + + + + Note that ATA bus errors can be reported as ATA device NCQ + errors. This should be handled as described in . + + + + If READ LOG EXT Log Page 10h fails or reports NQ, we're + thoroughly screwed. This condition should be treated + according to . + + + + + + ATA bus error + + + ATA bus error means that data corruption occurred during + transmission over ATA bus (SATA or PATA). This type of errors + can be indicated by + + + + + + + ICRC or ABRT error as described in . + + + + + + Controller-specific error completion with error information + indicating transmission error. + + + + + + On some controllers, command timeout. In this case, there may + be a mechanism to determine that the timeout is due to + transmission error. + + + + + + Unknown/random errors, timeouts and all sorts of weirdities. + + + + + + + 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. + + + + 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 for more information. + + + + + + PCI bus error + + + 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. + + + + + + Late completion + + + 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. + + + + + + Unknown error (timeout) + + + 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. + + + + Timeouts can also be caused by transmission errors. Refer to + for more details. + + + + + + Hotplug and power management exceptions + + + <<TODO: fill here>> + + + + + + + + EH recovery actions + + + This section discusses several important recovery actions. + + + + Clearing error condition + + + Many controllers require its error registers to be cleared by + error handler. Different controllers may have different + requirements. + + + + For SATA, it's strongly recommended to clear at least SError + register during error handling. + + + + + Reset + + + During EH, resetting is necessary in the following cases. + + + + + + + HSM is in unknown or invalid state + + + + + + HBA is in unknown or invalid state + + + + + + EH needs to make HBA/device forget about in-flight commands + + + + + + HBA/device behaves weirdly + + + + + + + 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. + + + + + + + When it's known that HBA is in ready state but ATA/ATAPI + device is in unknown state, reset only device. + + + + + + If HBA is in unknown state, reset both HBA and device. + + + + + + + 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. + + + + OTOH, ATA/ATAPI standard describes in detail ways to reset + ATA/ATAPI devices. + + + + + PATA hardware reset + + + 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. + + + + + Software reset + + + 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. + + + + + EXECUTE DEVICE DIAGNOSTIC command + + + 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. + + + 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. + + + + + ATAPI DEVICE RESET command + + + 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. + + + + + SATA phy reset + + + 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. + + + + + + + + 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. + + + + Parameters affected are. + + + + + + + CHS set up with INITIALIZE DEVICE PARAMETERS (seldom used) + + + + + + Parameters set with SET FEATURES including transfer mode setting + + + + + + Block count set with SET MULTIPLE MODE + + + + + + Other parameters (SET MAX, MEDIA LOCK...) + + + + + + + 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). + + + + 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. + + + + + + Reconfigure transport + + + 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. + + + + The following is a possible scheme Jeff Garzik suggested. + + +
+ + If more than $N (3?) transmission errors happen in 15 minutes, + + + + + if SATA, decrease SATA PHY speed. if speed cannot be decreased, + + + + + decrease UDMA xfer speed. if at UDMA0, switch to PIO4, + + + + + decrease PIO xfer speed. if at PIO3, complain, but continue + + + +
+ + + + + + + + + ata_piix Internals +!Idrivers/ata/ata_piix.c + + + + sata_sil Internals +!Idrivers/ata/sata_sil.c + + + + Thanks + + 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. + + + Thanks to Alan Cox for pointing out similarities + between SATA and SCSI, and in general for motivation to hack on + libata. + + + 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). + + + + -- cgit v1.2.3