Merge ../bleed-2.6

3 files changed, 1127 insertions, 63 deletions

diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl
index 375ae76..d260d92 100644
--- a/Documentation/DocBook/libata.tmpl
+++ b/Documentation/DocBook/libata.tmpl
@@ -415,6 +415,362 @@ and other resources, etc.
      </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 hostt->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/scsi/libata-core.c
@@ -431,6 +787,722 @@ and other resources, etc.
 !Idrivers/scsi/libata-scsi.c
   </chapter>
 
+  <chapter id="ataExceptions">
+     <title>ATA errors &amp; 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 excution 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 tranfer 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.  Upto
+	   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>
+	   Upto 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 upto
+	   ATA/ATAPI-7, it seems to imply that ABRT bit alone could
+	   indicate tranfer 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 upto 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 in 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 (seldomly 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/scsi/ata_piix.c
diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt
index 6dd274d..2d65c21 100644
--- a/Documentation/block/biodoc.txt
+++ b/Documentation/block/biodoc.txt
@@ -906,9 +906,20 @@ Aside:
 
 
 4. The I/O scheduler
-I/O schedulers are now per queue. They should be runtime switchable and modular
-but aren't yet. Jens has most bits to do this, but the sysfs implementation is
-missing.
+I/O scheduler, a.k.a. elevator, is implemented in two layers.  Generic dispatch
+queue and specific I/O schedulers.  Unless stated otherwise, elevator is used
+to refer to both parts and I/O scheduler to specific I/O schedulers.
+
+Block layer implements generic dispatch queue in ll_rw_blk.c and elevator.c.
+The generic dispatch queue is responsible for properly ordering barrier
+requests, requeueing, handling non-fs requests and all other subtleties.
+
+Specific I/O schedulers are responsible for ordering normal filesystem
+requests.  They can also choose to delay certain requests to improve
+throughput or whatever purpose.  As the plural form indicates, there are
+multiple I/O schedulers.  They can be built as modules but at least one should
+be built inside the kernel.  Each queue can choose different one and can also
+change to another one dynamically.
 
 A block layer call to the i/o scheduler follows the convention elv_xxx(). This
 calls elevator_xxx_fn in the elevator switch (drivers/block/elevator.c). Oh,
@@ -921,44 +932,36 @@ keeping work.
 The functions an elevator may implement are: (* are mandatory)
 elevator_merge_fn		called to query requests for merge with a bio
 
-elevator_merge_req_fn		" " "  with another request
+elevator_merge_req_fn		called when two requests get merged. the one
+				which gets merged into the other one will be
+				never seen by I/O scheduler again. IOW, after
+				being merged, the request is gone.
 
 elevator_merged_fn		called when a request in the scheduler has been
 				involved in a merge. It is used in the deadline
 				scheduler for example, to reposition the request
 				if its sorting order has changed.
 
-*elevator_next_req_fn		returns the next scheduled request, or NULL
-				if there are none (or none are ready).
+elevator_dispatch_fn		fills the dispatch queue with ready requests.
+				I/O schedulers are free to postpone requests by
+				not filling the dispatch queue unless @force
+				is non-zero.  Once dispatched, I/O schedulers
+				are not allowed to manipulate the requests -
+				they belong to generic dispatch queue.
 
-*elevator_add_req_fn		called to add a new request into the scheduler
+elevator_add_req_fn		called to add a new request into the scheduler
 
 elevator_queue_empty_fn		returns true if the merge queue is empty.
 				Drivers shouldn't use this, but rather check
 				if elv_next_request is NULL (without losing the
 				request if one exists!)
 
-elevator_remove_req_fn		This is called when a driver claims ownership of
-				the target request - it now belongs to the
-				driver. It must not be modified or merged.
-				Drivers must not lose the request! A subsequent
-				call of elevator_next_req_fn must  return the
-				_next_ request.
-
-elevator_requeue_req_fn		called to add a request to the scheduler. This
-				is used when the request has alrnadebeen
-				returned by elv_next_request, but hasn't
-				completed. If this is not implemented then
-				elevator_add_req_fn is called instead.
-
 elevator_former_req_fn
 elevator_latter_req_fn		These return the request before or after the
 				one specified in disk sort order. Used by the
 				block layer to find merge possibilities.
 
-elevator_completed_req_fn	called when a request is completed. This might
-				come about due to being merged with another or
-				when the device completes the request.
+elevator_completed_req_fn	called when a request is completed.
 
 elevator_may_queue_fn		returns true if the scheduler wants to allow the
 				current context to queue a new request even if
@@ -967,13 +970,33 @@ elevator_may_queue_fn		returns true if the scheduler wants to allow the
 
 elevator_set_req_fn
 elevator_put_req_fn		Must be used to allocate and free any elevator
-				specific storate for a request.
+				specific storage for a request.
+
+elevator_activate_req_fn	Called when device driver first sees a request.
+				I/O schedulers can use this callback to
+				determine when actual execution of a request
+				starts.
+elevator_deactivate_req_fn	Called when device driver decides to delay
+				a request by requeueing it.
 
 elevator_init_fn
 elevator_exit_fn		Allocate and free any elevator specific storage
 				for a queue.
 
-4.2 I/O scheduler implementation
+4.2 Request flows seen by I/O schedulers
+All requests seens by I/O schedulers strictly follow one of the following three
+flows.
+
+ set_req_fn ->
+
+ i.   add_req_fn -> (merged_fn ->)* -> dispatch_fn -> activate_req_fn ->
+      (deactivate_req_fn -> activate_req_fn ->)* -> completed_req_fn
+ ii.  add_req_fn -> (merged_fn ->)* -> merge_req_fn
+ iii. [none]
+
+ -> put_req_fn
+
+4.3 I/O scheduler implementation
 The generic i/o scheduler algorithm attempts to sort/merge/batch requests for
 optimal disk scan and request servicing performance (based on generic
 principles and device capabilities), optimized for:
@@ -993,18 +1016,7 @@ request in sort order to prevent binary tree lookups.
 This arrangement is not a generic block layer characteristic however, so
 elevators may implement queues as they please.
 
-ii. Last merge hint
-The last merge hint is part of the generic queue layer. I/O schedulers must do
-some management on it. For the most part, the most important thing is to make
-sure q->last_merge is cleared (set to NULL) when the request on it is no longer
-a candidate for merging (for example if it has been sent to the driver).
-
-The last merge performed is cached as a hint for the subsequent request. If
-sequential data is being submitted, the hint is used to perform merges without
-any scanning. This is not sufficient when there are multiple processes doing
-I/O though, so a "merge hash" is used by some schedulers.
-
-iii. Merge hash
+ii. Merge hash
 AS and deadline use a hash table indexed by the last sector of a request. This
 enables merging code to quickly look up "back merge" candidates, even when
 multiple I/O streams are being performed at once on one disk.
@@ -1013,29 +1025,8 @@ multiple I/O streams are being performed at once on one disk.
 are far less common than "back merges" due to the nature of most I/O patterns.
 Front merges are handled by the binary trees in AS and deadline schedulers.
 
-iv. Handling barrier cases
-A request with flags REQ_HARDBARRIER or REQ_SOFTBARRIER must not be ordered
-around. That is, they must be processed after all older requests, and before
-any newer ones. This includes merges!
-
-In AS and deadline schedulers, barriers have the effect of flushing the reorder
-queue. The performance cost of this will vary from nothing to a lot depending
-on i/o patterns and device characteristics. Obviously they won't improve
-performance, so their use should be kept to a minimum.
-
-v. Handling insertion position directives
-A request may be inserted with a position directive. The directives are one of
-ELEVATOR_INSERT_BACK, ELEVATOR_INSERT_FRONT, ELEVATOR_INSERT_SORT.
-
-ELEVATOR_INSERT_SORT is a general directive for non-barrier requests.
-ELEVATOR_INSERT_BACK is used to insert a barrier to the back of the queue.
-ELEVATOR_INSERT_FRONT is used to insert a barrier to the front of the queue, and
-overrides the ordering requested by any previous barriers. In practice this is
-harmless and required, because it is used for SCSI requeueing. This does not
-require flushing the reorder queue, so does not impose a performance penalty.
-
-vi. Plugging the queue to batch requests in anticipation of opportunities for
-  merge/sort optimizations
+iii. Plugging the queue to batch requests in anticipation of opportunities for
+     merge/sort optimizations
 
 This is just the same as in 2.4 so far, though per-device unplugging
 support is anticipated for 2.5. Also with a priority-based i/o scheduler,
@@ -1069,7 +1060,7 @@ Aside:
   blk_kick_queue() to unplug a specific queue (right away ?)
   or optionally, all queues, is in the plan.
 
-4.3 I/O contexts
+4.4 I/O contexts
 I/O contexts provide a dynamically allocated per process data area. They may
 be used in I/O schedulers, and in the block layer (could be used for IO statis,
 priorities for example). See *io_context in drivers/block/ll_rw_blk.c, and
diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt
index a55f0f9..b0fe41d 100644
--- a/Documentation/networking/bonding.txt
+++ b/Documentation/networking/bonding.txt
@@ -777,7 +777,7 @@ doing so is the same as described in the "Configuring Multiple Bonds
 Manually" section, below.
 
 	NOTE: It has been observed that some Red Hat supplied kernels
-are apparently unable to rename modules at load time (the "-obonding1"
+are apparently unable to rename modules at load time (the "-o bond1"
 part).  Attempts to pass that option to modprobe will produce an
 "Operation not permitted" error.  This has been reported on some
 Fedora Core kernels, and has been seen on RHEL 4 as well.  On kernels
@@ -883,7 +883,8 @@ the above does not work, and the second bonding instance never sees
 its options.  In that case, the second options line can be substituted
 as follows:
 
-install bonding1 /sbin/modprobe bonding -obond1 mode=balance-alb miimon=50
+install bond1 /sbin/modprobe --ignore-install bonding -o bond1 \
+	mode=balance-alb miimon=50
 
 	This may be repeated any number of times, specifying a new and
 unique name in place of bond1 for each subsequent instance.