Documentation/PCI/pcieaer-howto.rst - linux - Git at Google

 .. SPDX-License-Identifier: GPL-2.0
 .. include:: <isonum.txt>

 ===========================================================
 The PCI Express Advanced Error Reporting Driver Guide HOWTO
 ===========================================================

 :Authors: - T. Long Nguyen <tom.l.nguyen@intel.com>
           - Yanmin Zhang <yanmin.zhang@intel.com>

 :Copyright: |copy| 2006 Intel Corporation

 Overview
 ===========

 About this guide
 ----------------

 This guide describes the basics of the PCI Express (PCIe) Advanced Error
 Reporting (AER) driver and provides information on how to use it, as
 well as how to enable the drivers of Endpoint devices to conform with
 the PCIe AER driver.


 What is the PCIe AER Driver?
 ----------------------------

 PCIe error signaling can occur on the PCIe link itself
 or on behalf of transactions initiated on the link. PCIe
 defines two error reporting paradigms: the baseline capability and
 the Advanced Error Reporting capability. The baseline capability is
 required of all PCIe components providing a minimum defined
 set of error reporting requirements. Advanced Error Reporting
 capability is implemented with a PCIe Advanced Error Reporting
 extended capability structure providing more robust error reporting.

 The PCIe AER driver provides the infrastructure to support PCIe Advanced
 Error Reporting capability. The PCIe AER driver provides three basic
 functions:

   - Gathers the comprehensive error information if errors occurred.
   - Reports error to the users.
   - Performs error recovery actions.

 The AER driver only attaches to Root Ports and RCECs that support the PCIe
 AER capability.


 User Guide
 ==========

 Include the PCIe AER Root Driver into the Linux Kernel
 ------------------------------------------------------

 The PCIe AER driver is a Root Port service driver attached
 via the PCIe Port Bus driver. If a user wants to use it, the driver
 must be compiled. It is enabled with CONFIG_PCIEAER, which
 depends on CONFIG_PCIEPORTBUS.

 Load PCIe AER Root Driver
 -------------------------

 Some systems have AER support in firmware. Enabling Linux AER support at
 the same time the firmware handles AER would result in unpredictable
 behavior. Therefore, Linux does not handle AER events unless the firmware
 grants AER control to the OS via the ACPI _OSC method. See the PCI Firmware
 Specification for details regarding _OSC usage.

 AER error output
 ----------------

 When a PCIe AER error is captured, an error message will be output to
 console. If it's a correctable error, it is output as an info message.
 Otherwise, it is printed as an error. So users could choose different
 log level to filter out correctable error messages.

 Below shows an example::

   0000:50:00.0: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, id=0500(Requester ID)
   0000:50:00.0:   device [8086:0329] error status/mask=00100000/00000000
   0000:50:00.0:    [20] Unsupported Request    (First)
   0000:50:00.0:   TLP Header: 04000001 00200a03 05010000 00050100

 In the example, 'Requester ID' means the ID of the device that sent
 the error message to the Root Port. Please refer to PCIe specs for other
 fields.

 AER Statistics / Counters
 -------------------------

 When PCIe AER errors are captured, the counters / statistics are also exposed
 in the form of sysfs attributes which are documented at
 Documentation/ABI/testing/sysfs-bus-pci-devices-aer_stats

 Developer Guide
 ===============

 To enable error recovery, a software driver must provide callbacks.

 To support AER better, developers need to understand how AER works.

 PCIe errors are classified into two types: correctable errors
 and uncorrectable errors. This classification is based on the impact
 of those errors, which may result in degraded performance or function
 failure.

 Correctable errors pose no impacts on the functionality of the
 interface. The PCIe protocol can recover without any software
 intervention or any loss of data. These errors are detected and
 corrected by hardware.

 Unlike correctable errors, uncorrectable
 errors impact functionality of the interface. Uncorrectable errors
 can cause a particular transaction or a particular PCIe link
 to be unreliable. Depending on those error conditions, uncorrectable
 errors are further classified into non-fatal errors and fatal errors.
 Non-fatal errors cause the particular transaction to be unreliable,
 but the PCIe link itself is fully functional. Fatal errors, on
 the other hand, cause the link to be unreliable.

 When PCIe error reporting is enabled, a device will automatically send an
 error message to the Root Port above it when it captures
 an error. The Root Port, upon receiving an error reporting message,
 internally processes and logs the error message in its AER
 Capability structure. Error information being logged includes storing
 the error reporting agent's requestor ID into the Error Source
 Identification Registers and setting the error bits of the Root Error
 Status Register accordingly. If AER error reporting is enabled in the Root
 Error Command Register, the Root Port generates an interrupt when an
 error is detected.

 Note that the errors as described above are related to the PCIe
 hierarchy and links. These errors do not include any device specific
 errors because device specific errors will still get sent directly to
 the device driver.

 Provide callbacks
 -----------------

 callback reset_link to reset PCIe link
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 This callback is used to reset the PCIe physical link when a
 fatal error happens. The Root Port AER service driver provides a
 default reset_link function, but different Upstream Ports might
 have different specifications to reset the PCIe link, so
 Upstream Port drivers may provide their own reset_link functions.

 Section 3.2.2.2 provides more detailed info on when to call
 reset_link.

 PCI error-recovery callbacks
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 The PCIe AER Root driver uses error callbacks to coordinate
 with downstream device drivers associated with a hierarchy in question
 when performing error recovery actions.

 Data struct pci_driver has a pointer, err_handler, to point to
 pci_error_handlers who consists of a couple of callback function
 pointers. The AER driver follows the rules defined in
 pci-error-recovery.rst except PCIe-specific parts (e.g.
 reset_link). Please refer to pci-error-recovery.rst for detailed
 definitions of the callbacks.

 The sections below specify when to call the error callback functions.

 Correctable errors
 ~~~~~~~~~~~~~~~~~~

 Correctable errors pose no impacts on the functionality of
 the interface. The PCIe protocol can recover without any
 software intervention or any loss of data. These errors do not
 require any recovery actions. The AER driver clears the device's
 correctable error status register accordingly and logs these errors.

 Non-correctable (non-fatal and fatal) errors
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 If an error message indicates a non-fatal error, performing link reset
 at upstream is not required. The AER driver calls error_detected(dev,
 pci_channel_io_normal) to all drivers associated within a hierarchy in
 question. For example::

   Endpoint <==> Downstream Port B <==> Upstream Port A <==> Root Port

 If Upstream Port A captures an AER error, the hierarchy consists of
 Downstream Port B and Endpoint.

 A driver may return PCI_ERS_RESULT_CAN_RECOVER,
 PCI_ERS_RESULT_DISCONNECT, or PCI_ERS_RESULT_NEED_RESET, depending on
 whether it can recover or the AER driver calls mmio_enabled as next.

 If an error message indicates a fatal error, kernel will broadcast
 error_detected(dev, pci_channel_io_frozen) to all drivers within
 a hierarchy in question. Then, performing link reset at upstream is
 necessary. As different kinds of devices might use different approaches
 to reset link, AER port service driver is required to provide the
 function to reset link via callback parameter of pcie_do_recovery()
 function. If reset_link is not NULL, recovery function will use it
 to reset the link. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER
 and reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes
 to mmio_enabled.

 Frequent Asked Questions
 ------------------------

 Q:
   What happens if a PCIe device driver does not provide an
   error recovery handler (pci_driver->err_handler is equal to NULL)?

 A:
   The devices attached with the driver won't be recovered. If the
   error is fatal, kernel will print out warning messages. Please refer
   to section 3 for more information.

 Q:
   What happens if an upstream port service driver does not provide
   callback reset_link?

 A:
   Fatal error recovery will fail if the errors are reported by the
   upstream ports who are attached by the service driver.


 Software error injection
 ========================

 Debugging PCIe AER error recovery code is quite difficult because it
 is hard to trigger real hardware errors. Software based error
 injection can be used to fake various kinds of PCIe errors.

 First you should enable PCIe AER software error injection in kernel
 configuration, that is, following item should be in your .config.

 CONFIG_PCIEAER_INJECT=y or CONFIG_PCIEAER_INJECT=m

 After reboot with new kernel or insert the module, a device file named
 /dev/aer_inject should be created.

 Then, you need a user space tool named aer-inject, which can be gotten
 from:

     https://github.com/intel/aer-inject.git

 More information about aer-inject can be found in the document in
 its source code.
	.. SPDX-License-Identifier: GPL-2.0
	.. include:: <isonum.txt>

	===========================================================
	The PCI Express Advanced Error Reporting Driver Guide HOWTO
	===========================================================

	:Authors: - T. Long Nguyen <tom.l.nguyen@intel.com>
	- Yanmin Zhang <yanmin.zhang@intel.com>

	:Copyright: \|copy\| 2006 Intel Corporation

	Overview
	===========

	About this guide
	----------------

	This guide describes the basics of the PCI Express (PCIe) Advanced Error
	Reporting (AER) driver and provides information on how to use it, as
	well as how to enable the drivers of Endpoint devices to conform with
	the PCIe AER driver.


	What is the PCIe AER Driver?
	----------------------------

	PCIe error signaling can occur on the PCIe link itself
	or on behalf of transactions initiated on the link. PCIe
	defines two error reporting paradigms: the baseline capability and
	the Advanced Error Reporting capability. The baseline capability is
	required of all PCIe components providing a minimum defined
	set of error reporting requirements. Advanced Error Reporting
	capability is implemented with a PCIe Advanced Error Reporting
	extended capability structure providing more robust error reporting.

	The PCIe AER driver provides the infrastructure to support PCIe Advanced
	Error Reporting capability. The PCIe AER driver provides three basic
	functions:

	- Gathers the comprehensive error information if errors occurred.
	- Reports error to the users.
	- Performs error recovery actions.

	The AER driver only attaches to Root Ports and RCECs that support the PCIe
	AER capability.


	User Guide
	==========

	Include the PCIe AER Root Driver into the Linux Kernel
	------------------------------------------------------

	The PCIe AER driver is a Root Port service driver attached
	via the PCIe Port Bus driver. If a user wants to use it, the driver
	must be compiled. It is enabled with CONFIG_PCIEAER, which
	depends on CONFIG_PCIEPORTBUS.

	Load PCIe AER Root Driver
	-------------------------

	Some systems have AER support in firmware. Enabling Linux AER support at
	the same time the firmware handles AER would result in unpredictable
	behavior. Therefore, Linux does not handle AER events unless the firmware
	grants AER control to the OS via the ACPI _OSC method. See the PCI Firmware
	Specification for details regarding _OSC usage.

	AER error output
	----------------

	When a PCIe AER error is captured, an error message will be output to
	console. If it's a correctable error, it is output as an info message.
	Otherwise, it is printed as an error. So users could choose different
	log level to filter out correctable error messages.

	Below shows an example::

	0000:50:00.0: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, id=0500(Requester ID)
	0000:50:00.0: device [8086:0329] error status/mask=00100000/00000000
	0000:50:00.0: [20] Unsupported Request (First)
	0000:50:00.0: TLP Header: 04000001 00200a03 05010000 00050100

	In the example, 'Requester ID' means the ID of the device that sent
	the error message to the Root Port. Please refer to PCIe specs for other
	fields.

	AER Statistics / Counters
	-------------------------

	When PCIe AER errors are captured, the counters / statistics are also exposed
	in the form of sysfs attributes which are documented at
	Documentation/ABI/testing/sysfs-bus-pci-devices-aer_stats

	Developer Guide
	===============

	To enable error recovery, a software driver must provide callbacks.

	To support AER better, developers need to understand how AER works.

	PCIe errors are classified into two types: correctable errors
	and uncorrectable errors. This classification is based on the impact
	of those errors, which may result in degraded performance or function
	failure.

	Correctable errors pose no impacts on the functionality of the
	interface. The PCIe protocol can recover without any software
	intervention or any loss of data. These errors are detected and
	corrected by hardware.

	Unlike correctable errors, uncorrectable
	errors impact functionality of the interface. Uncorrectable errors
	can cause a particular transaction or a particular PCIe link
	to be unreliable. Depending on those error conditions, uncorrectable
	errors are further classified into non-fatal errors and fatal errors.
	Non-fatal errors cause the particular transaction to be unreliable,
	but the PCIe link itself is fully functional. Fatal errors, on
	the other hand, cause the link to be unreliable.

	When PCIe error reporting is enabled, a device will automatically send an
	error message to the Root Port above it when it captures
	an error. The Root Port, upon receiving an error reporting message,
	internally processes and logs the error message in its AER
	Capability structure. Error information being logged includes storing
	the error reporting agent's requestor ID into the Error Source
	Identification Registers and setting the error bits of the Root Error
	Status Register accordingly. If AER error reporting is enabled in the Root
	Error Command Register, the Root Port generates an interrupt when an
	error is detected.

	Note that the errors as described above are related to the PCIe
	hierarchy and links. These errors do not include any device specific
	errors because device specific errors will still get sent directly to
	the device driver.

	Provide callbacks
	-----------------

	callback reset_link to reset PCIe link
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	This callback is used to reset the PCIe physical link when a
	fatal error happens. The Root Port AER service driver provides a
	default reset_link function, but different Upstream Ports might
	have different specifications to reset the PCIe link, so
	Upstream Port drivers may provide their own reset_link functions.

	Section 3.2.2.2 provides more detailed info on when to call
	reset_link.

	PCI error-recovery callbacks
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	The PCIe AER Root driver uses error callbacks to coordinate
	with downstream device drivers associated with a hierarchy in question
	when performing error recovery actions.

	Data struct pci_driver has a pointer, err_handler, to point to
	pci_error_handlers who consists of a couple of callback function
	pointers. The AER driver follows the rules defined in
	pci-error-recovery.rst except PCIe-specific parts (e.g.
	reset_link). Please refer to pci-error-recovery.rst for detailed
	definitions of the callbacks.

	The sections below specify when to call the error callback functions.

	Correctable errors
	~~~~~~~~~~~~~~~~~~

	Correctable errors pose no impacts on the functionality of
	the interface. The PCIe protocol can recover without any
	software intervention or any loss of data. These errors do not
	require any recovery actions. The AER driver clears the device's
	correctable error status register accordingly and logs these errors.

	Non-correctable (non-fatal and fatal) errors
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	If an error message indicates a non-fatal error, performing link reset
	at upstream is not required. The AER driver calls error_detected(dev,
	pci_channel_io_normal) to all drivers associated within a hierarchy in
	question. For example::

	Endpoint <==> Downstream Port B <==> Upstream Port A <==> Root Port

	If Upstream Port A captures an AER error, the hierarchy consists of
	Downstream Port B and Endpoint.

	A driver may return PCI_ERS_RESULT_CAN_RECOVER,
	PCI_ERS_RESULT_DISCONNECT, or PCI_ERS_RESULT_NEED_RESET, depending on
	whether it can recover or the AER driver calls mmio_enabled as next.

	If an error message indicates a fatal error, kernel will broadcast
	error_detected(dev, pci_channel_io_frozen) to all drivers within
	a hierarchy in question. Then, performing link reset at upstream is
	necessary. As different kinds of devices might use different approaches
	to reset link, AER port service driver is required to provide the
	function to reset link via callback parameter of pcie_do_recovery()
	function. If reset_link is not NULL, recovery function will use it
	to reset the link. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER
	and reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes
	to mmio_enabled.

	Frequent Asked Questions
	------------------------

	Q:
	What happens if a PCIe device driver does not provide an
	error recovery handler (pci_driver->err_handler is equal to NULL)?

	A:
	The devices attached with the driver won't be recovered. If the
	error is fatal, kernel will print out warning messages. Please refer
	to section 3 for more information.

	Q:
	What happens if an upstream port service driver does not provide
	callback reset_link?

	A:
	Fatal error recovery will fail if the errors are reported by the
	upstream ports who are attached by the service driver.


	Software error injection
	========================

	Debugging PCIe AER error recovery code is quite difficult because it
	is hard to trigger real hardware errors. Software based error
	injection can be used to fake various kinds of PCIe errors.

	First you should enable PCIe AER software error injection in kernel
	configuration, that is, following item should be in your .config.

	CONFIG_PCIEAER_INJECT=y or CONFIG_PCIEAER_INJECT=m

	After reboot with new kernel or insert the module, a device file named
	/dev/aer_inject should be created.

	Then, you need a user space tool named aer-inject, which can be gotten
	from:

	https://github.com/intel/aer-inject.git

	More information about aer-inject can be found in the document in
	its source code.