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Lukas Wunner d0a2dee7d4 PCI/AER: Allow drivers to opt in to Bus Reset on Non-Fatal Errors 
When Advanced Error Reporting was introduced in September 2006 by commit
6c2b374d74 ("PCI-Express AER implemetation: AER core and aerdriver"), it
sought to adhere to the recovery flow and callbacks specified in
Documentation/PCI/pci-error-recovery.rst.

That document had been added in January 2006, when Enhanced Error Handling
(EEH) was introduced for PowerPC with commit 065c635907 ("[PATCH] PCI
Error Recovery: documentation").

However the AER driver deviates from the document in that it never
performs a Secondary Bus Reset on Non-Fatal Errors, but always on Fatal
Errors.  By contrast, EEH allows drivers to opt in or out of a Bus Reset
regardless of error severity, by returning PCI_ERS_RESULT_NEED_RESET or
PCI_ERS_RESULT_CAN_RECOVER from their ->error_detected() callback.  If all
drivers agree that they can recover without a Bus Reset, EEH skips it.
Should one of them request a Bus Reset, it overrides all other drivers.

This inconsistency between EEH and AER seems problematic because drivers
need to be aware of and cope with it.

The file Documentation/PCI/pcieaer-howto.rst hints at a rationale for
always performing a Bus Reset on Fatal Errors:  "Fatal errors [...] cause
the link to be unreliable.  [...] This [reset_link] callback is used to
reset the PCIe physical link when a fatal error happens.  If an error
message indicates a fatal error, [...] performing link reset at upstream
is necessary."

There's no such rationale provided for never performing a Bus Reset on
Non-Fatal Errors.

The "xe" driver has a need to attempt a reset of local units on graphics
cards upon a Non-Fatal Error.  If that is insufficient for recovery, the
driver wants to opt in to a Bus Reset.

Accommodate such use cases and align AER more closely with EEH by
performing a Bus Reset in pcie_do_recovery() if drivers request it and the
faulting device's channel_state is pci_channel_io_normal.  The AER driver
sets this channel_state for Non-Fatal Errors.  For Fatal Errors, it uses
pci_channel_io_frozen.

This limits the deviation from Documentation/PCI/pci-error-recovery.rst
and EEH to the unconditional Bus Reset on Fatal Errors.

pcie_do_recovery() is also invoked by the Downstream Port Containment and
Error Disconnect Recover drivers.  They both set the channel_state to
pci_channel_io_frozen, hence pcie_do_recovery() continues to always invoke
the ->reset_subordinates() callback in their case.  That is necessary
because the callback brings the link back up at the containing Downstream
Port.

There are two behavioral changes resulting from this commit:

First, if channel_state is pci_channel_io_normal and one of the affected
drivers returns PCI_ERS_RESULT_NEED_RESET from its ->error_detected()
callback, a Bus Reset will now be performed.  There are drivers doing this
and although it would be possible to avoid a behavioral change by letting
them return PCI_ERS_RESULT_CAN_RECOVER instead, the impression I got from
examination of all drivers is that they actually expect or want a Bus
Reset (cxl_error_detected() is a case in point).  In any case, if they can
cope with a Bus Reset on Fatal Errors, they shouldn't have issues with a
Bus Reset on Non-Fatal Errors.

Second, if channel_state is pci_channel_io_frozen and all affected drivers
return PCI_ERS_RESULT_CAN_RECOVER from ->error_detected(), their
->mmio_enabled() callback is now invoked prior to performing a Bus Reset,
instead of afterwards.  This actually makes sense:  For example,
drivers/scsi/sym53c8xx_2/sym_glue.c dumps debug registers in its
->mmio_enabled() callback.  Doing so after reset right now captures the
post-reset state instead of the faulting state, which is useless.

There is only one other driver which implements ->mmio_enabled() and
returns PCI_ERS_RESULT_CAN_RECOVER from ->error_detected() for
channel_state pci_channel_io_frozen, drivers/scsi/ipr.c (IBM Power RAID).
It appears to only be used on EEH platforms.  So the second behavioral
change is limited to these two drivers.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/28fd805043bb57af390168d05abb30898cf4fc58.1755008151.git.lukas@wunner.de
History 2025-08-13 13:20:26 -05:00
arch - Fix an interrupt vector setup race which leads to a non-functioning device 2025-08-10 08:15:32 +03:00
block block-6.17-20250808 2025-08-09 08:47:28 +03:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
Documentation EFI updates for v6.17 2025-08-09 18:10:01 +03:00
drivers PCI/AER: Allow drivers to opt in to Bus Reset on Non-Fatal Errors 2025-08-13 13:20:26 -05:00
fs NFS client updates for Linux 6.17 2025-08-09 07:20:44 +03:00
include TTY revert fix for 6.16-rc1 2025-08-09 18:12:23 +03:00
init Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
io_uring io_uring/memmap: cast nr_pages to size_t before shifting 2025-08-08 06:35:14 -06:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel - Remove an obsolete comment and fix spelling 2025-08-10 08:51:37 +03:00
lib block-6.17-20250808 2025-08-09 08:47:28 +03:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm Significant patch series in this pull request: 2025-08-05 16:02:07 +03:00
net NFS client updates for Linux 6.17 2025-08-09 07:20:44 +03:00
rust Rust changes for v6.17 2025-08-03 13:49:10 -07:00
samples Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
scripts Kbuild updates for v6.17 2025-08-06 07:32:52 +03:00
security + Features 2025-08-04 08:17:28 -07:00
sound gpio updates for v6.17-rc1 2025-08-09 08:15:43 +03:00
tools tools/power turbostat: version 2025.09.09 2025-08-10 09:02:36 +03:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge tag 'kvm-x86-no_assignment-6.17' of https://github.com/kvm-x86/linux into HEAD 2025-07-29 08:36:42 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore gitignore: allow .pylintrc to be tracked 2025-07-02 17:10:04 -06:00
.mailmap Significant patch series in this pull request: 2025-08-03 16:23:09 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Kbuild updates for v6.17 2025-08-06 07:32:52 +03:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS spi: Fixes for v6.17 2025-08-09 08:43:24 +03:00
Makefile Linux 6.17-rc1 2025-08-10 19:41:16 +03:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.