|author||Mike Mason <firstname.lastname@example.org>||2009-07-30 15:39:29 -0700|
|committer||Jesse Barnes <email@example.com>||2009-09-09 13:29:38 -0700|
PCI: document PCIe fundamental reset interfaces
The attached patch updates the Documentation/PCI/pci-error-recovery.txt file with changes related to this new bit field, as well a few unrelated updates. Signed-off-by: Linas Vepstas <firstname.lastname@example.org> Signed-off-by: Mike Mason <email@example.com> Signed-off-by: Richard Lary <firstname.lastname@example.org> Signed-off-by: Jesse Barnes <email@example.com>
Diffstat (limited to 'Documentation/PCI')
1 files changed, 77 insertions, 42 deletions
diff --git a/Documentation/PCI/pci-error-recovery.txt b/Documentation/PCI/pci-error-recovery.txt
index 6650af432523..e83f2ea76415 100644
@@ -4,15 +4,17 @@
February 2, 2006
Current document maintainer:
- Linas Vepstas <firstname.lastname@example.org>
+ Linas Vepstas <email@example.com>
+ updated by Richard Lary <firstname.lastname@example.org>
+ and Mike Mason <email@example.com> on 27-Jul-2009
Many PCI bus controllers are able to detect a variety of hardware
PCI errors on the bus, such as parity errors on the data and address
busses, as well as SERR and PERR errors. Some of the more advanced
chipsets are able to deal with these errors; these include PCI-E chipsets,
-and the PCI-host bridges found on IBM Power4 and Power5-based pSeries
-boxes. A typical action taken is to disconnect the affected device,
+and the PCI-host bridges found on IBM Power4, Power5 and Power6-based
+pSeries boxes. A typical action taken is to disconnect the affected device,
halting all I/O to it. The goal of a disconnection is to avoid system
corruption; for example, to halt system memory corruption due to DMA's
to "wild" addresses. Typically, a reconnection mechanism is also
@@ -37,10 +39,11 @@ is forced by the need to handle multi-function devices, that is,
devices that have multiple device drivers associated with them.
In the first stage, each driver is allowed to indicate what type
of reset it desires, the choices being a simple re-enabling of I/O
-or requesting a hard reset (a full electrical #RST of the PCI card).
-If any driver requests a full reset, that is what will be done.
+or requesting a slot reset.
-After a full reset and/or a re-enabling of I/O, all drivers are
+If any driver requests a slot reset, that is what will be done.
+After a reset and/or a re-enabling of I/O, all drivers are
again notified, so that they may then perform any device setup/config
that may be required. After these have all completed, a final
"resume normal operations" event is sent out.
@@ -101,7 +104,7 @@ if it implements any, it must implement error_detected(). If a callback
is not implemented, the corresponding feature is considered unsupported.
For example, if mmio_enabled() and resume() aren't there, then it
is assumed that the driver is not doing any direct recovery and requires
-a reset. If link_reset() is not implemented, the card is assumed as
+a slot reset. If link_reset() is not implemented, the card is assumed to
not care about link resets. Typically a driver will want to know about
@@ -111,7 +114,7 @@ sequence described below.
STEP 0: Error Event
-PCI bus error is detect by the PCI hardware. On powerpc, the slot
+A PCI bus error is detected by the PCI hardware. On powerpc, the slot
is isolated, in that all I/O is blocked: all reads return 0xffffffff,
all writes are ignored.
@@ -139,7 +142,7 @@ The driver must return one of the following result codes:
a chance to extract some diagnostic information (see
- Driver returns this if it can't recover without a hard
+ Driver returns this if it can't recover without a
Driver returns this if it doesn't want to recover at all.
@@ -169,11 +172,11 @@ is STEP 6 (Permanent Failure).
>>> The current powerpc implementation doesn't much care if the device
>>> attempts I/O at this point, or not. I/O's will fail, returning
->>> a value of 0xff on read, and writes will be dropped. If the device
->>> driver attempts more than 10K I/O's to a frozen adapter, it will
->>> assume that the device driver has gone into an infinite loop, and
->>> it will panic the kernel. There doesn't seem to be any other
->>> way of stopping a device driver that insists on spinning on I/O.
+>>> a value of 0xff on read, and writes will be dropped. If more than
+>>> EEH_MAX_FAILS I/O's are attempted to a frozen adapter, EEH
+>>> assumes that the device driver has gone into an infinite loop
+>>> and prints an error to syslog. A reboot is then required to
+>>> get the device working again.
STEP 2: MMIO Enabled
@@ -182,15 +185,14 @@ DMA), and then calls the mmio_enabled() callback on all affected
This is the "early recovery" call. IOs are allowed again, but DMA is
-not (hrm... to be discussed, I prefer not), with some restrictions. This
-is NOT a callback for the driver to start operations again, only to
-peek/poke at the device, extract diagnostic information, if any, and
-eventually do things like trigger a device local reset or some such,
-but not restart operations. This is callback is made if all drivers on
-a segment agree that they can try to recover and if no automatic link reset
-was performed by the HW. If the platform can't just re-enable IOs without
-a slot reset or a link reset, it wont call this callback, and instead
-will have gone directly to STEP 3 (Link Reset) or STEP 4 (Slot Reset)
+not, with some restrictions. This is NOT a callback for the driver to
+start operations again, only to peek/poke at the device, extract diagnostic
+information, if any, and eventually do things like trigger a device local
+reset or some such, but not restart operations. This callback is made if
+all drivers on a segment agree that they can try to recover and if no automatic
+link reset was performed by the HW. If the platform can't just re-enable IOs
+without a slot reset or a link reset, it will not call this callback, and
+instead will have gone directly to STEP 3 (Link Reset) or STEP 4 (Slot Reset)
>>> The following is proposed; no platform implements this yet:
>>> Proposal: All I/O's should be done _synchronously_ from within
@@ -228,9 +230,6 @@ proceeds to either STEP3 (Link Reset) or to STEP 5 (Resume Operations).
If any driver returned PCI_ERS_RESULT_NEED_RESET, then the platform
proceeds to STEP 4 (Slot Reset)
->>> The current powerpc implementation does not implement this callback.
STEP 3: Link Reset
The platform resets the link, and then calls the link_reset() callback
@@ -253,16 +252,33 @@ The platform then proceeds to either STEP 4 (Slot Reset) or STEP 5
>>> The current powerpc implementation does not implement this callback.
STEP 4: Slot Reset
-The platform performs a soft or hard reset of the device, and then
-calls the slot_reset() callback.
-A soft reset consists of asserting the adapter #RST line and then
+In response to a return value of PCI_ERS_RESULT_NEED_RESET, the
+the platform will peform a slot reset on the requesting PCI device(s).
+The actual steps taken by a platform to perform a slot reset
+will be platform-dependent. Upon completion of slot reset, the
+platform will call the device slot_reset() callback.
+Powerpc platforms implement two levels of slot reset:
+soft reset(default) and fundamental(optional) reset.
+Powerpc soft reset consists of asserting the adapter #RST line and then
restoring the PCI BAR's and PCI configuration header to a state
that is equivalent to what it would be after a fresh system
power-on followed by power-on BIOS/system firmware initialization.
+Soft reset is also known as hot-reset.
+Powerpc fundamental reset is supported by PCI Express cards only
+and results in device's state machines, hardware logic, port states and
+configuration registers to initialize to their default conditions.
+For most PCI devices, a soft reset will be sufficient for recovery.
+Optional fundamental reset is provided to support a limited number
+of PCI Express PCI devices for which a soft reset is not sufficient
If the platform supports PCI hotplug, then the reset might be
performed by toggling the slot electrical power off/on.
@@ -274,10 +290,12 @@ may result in hung devices, kernel panics, or silent data corruption.
This call gives drivers the chance to re-initialize the hardware
(re-download firmware, etc.). At this point, the driver may assume
-that he card is in a fresh state and is fully functional. In
-particular, interrupt generation should work normally.
+that the card is in a fresh state and is fully functional. The slot
+is unfrozen and the driver has full access to PCI config space,
+memory mapped I/O space and DMA. Interrupts (Legacy, MSI, or MSI-X)
+will also be available.
-Drivers should not yet restart normal I/O processing operations
+Drivers should not restart normal I/O processing operations
at this point. If all device drivers report success on this
callback, the platform will call resume() to complete the sequence,
and let the driver restart normal I/O processing.
@@ -302,11 +320,21 @@ driver performs device init only from PCI function 0:
Same as above.
+Drivers for PCI Express cards that require a fundamental reset must
+set the needs_freset bit in the pci_dev structure in their probe function.
+For example, the QLogic qla2xxx driver sets the needs_freset bit for certain
+PCI card types:
++ /* Set EEH reset type to fundamental if required by hba */
++ if (IS_QLA24XX(ha) || IS_QLA25XX(ha) || IS_QLA81XX(ha))
++ pdev->needs_freset = 1;
Platform proceeds either to STEP 5 (Resume Operations) or STEP 6 (Permanent
->>> The current powerpc implementation does not currently try a
->>> power-cycle reset if the driver returned PCI_ERS_RESULT_DISCONNECT.
+>>> The current powerpc implementation does not try a power-cycle
+>>> reset if the driver returned PCI_ERS_RESULT_DISCONNECT.
>>> However, it probably should.
@@ -348,7 +376,7 @@ software errors.
Conclusion; General Remarks
-The way those callbacks are called is platform policy. A platform with
+The way the callbacks are called is platform policy. A platform with
no slot reset capability may want to just "ignore" drivers that can't
recover (disconnect them) and try to let other cards on the same segment
recover. Keep in mind that in most real life cases, though, there will
@@ -361,8 +389,8 @@ That is, the recovery API only requires that:
- There is no guarantee that interrupt delivery can proceed from any
device on the segment starting from the error detection and until the
-resume callback is sent, at which point interrupts are expected to be
+slot_reset callback is called, at which point interrupts are expected
+to be fully operational.
- There is no guarantee that interrupt delivery is stopped, that is,
a driver that gets an interrupt after detecting an error, or that detects
@@ -381,16 +409,23 @@ anyway :)
>>> Implementation details for the powerpc platform are discussed in
>>> the file Documentation/powerpc/eeh-pci-error-recovery.txt
->>> As of this writing, there are six device drivers with patches
->>> implementing error recovery. Not all of these patches are in
+>>> As of this writing, there is a growing list of device drivers with
+>>> patches implementing error recovery. Not all of these patches are in
>>> mainline yet. These may be used as "examples":