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diff --git a/Documentation/PCI/pcieaer-howto.rst b/Documentation/PCI/pcieaer-howto.rst index 0b36b9ebfa4b..3210c4792978 100644 --- a/Documentation/PCI/pcieaer-howto.rst +++ b/Documentation/PCI/pcieaer-howto.rst @@ -16,264 +16,221 @@ Overview About this guide ---------------- -This guide describes the basics of the PCI Express Advanced Error +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 -PCI Express AER driver. +well as how to enable the drivers of Endpoint devices to conform with +the PCIe AER driver. -What is the PCI Express AER Driver? ------------------------------------ +What is the PCIe AER Driver? +---------------------------- -PCI Express error signaling can occur on the PCI Express link itself -or on behalf of transactions initiated on the link. PCI Express +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 PCI Express components providing a minimum defined +required of all PCIe components providing a minimum defined set of error reporting requirements. Advanced Error Reporting -capability is implemented with a PCI Express advanced error reporting +capability is implemented with a PCIe Advanced Error Reporting extended capability structure providing more robust error reporting. -The PCI Express AER driver provides the infrastructure to support PCI -Express Advanced Error Reporting capability. The PCI Express AER -driver provides three basic functions: +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. -AER driver only attaches root ports which support PCI-Express AER -capability. +The AER driver only attaches to Root Ports and RCECs that support the PCIe +AER capability. User Guide ========== -Include the PCI Express AER Root Driver into the Linux Kernel -------------------------------------------------------------- +Include the PCIe AER Root Driver into the Linux Kernel +------------------------------------------------------ -The PCI Express AER Root driver is a Root Port service driver attached -to the PCI Express Port Bus driver. If a user wants to use it, the driver -has to be compiled. Option CONFIG_PCIEAER supports this capability. It -depends on CONFIG_PCIEPORTBUS, so pls. set CONFIG_PCIEPORTBUS=y and -CONFIG_PCIEAER = y. +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 PCI Express AER Root Driver --------------------------------- +Load PCIe AER Root Driver +------------------------- Some systems have AER support in firmware. Enabling Linux AER support at -the same time the firmware handles AER may result in unpredictable +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 FW 3.0 +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 a warning. +console. If it's a correctable error, it is output as a warning 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: PCIe Bus Error: severity=Uncorrectable (Fatal), type=Transaction Layer, (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 + 0000:50:00.0: [20] UnsupReq (First) + 0000:50:00.0: TLP Header: 0x04000001 0x00200a03 0x05010000 0x00050100 + +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 Ratelimits +-------------- + +Since error messages can be generated for each transaction, we may see +large volumes of errors reported. To prevent spammy devices from flooding +the console/stalling execution, messages are throttled by device and error +type (correctable vs. non-fatal uncorrectable). Fatal errors, including +DPC errors, are not ratelimited. + +AER uses the default ratelimit of DEFAULT_RATELIMIT_BURST (10 events) over +DEFAULT_RATELIMIT_INTERVAL (5 seconds). -In the example, 'Requester ID' means the ID of the device who sends -the error message to root port. Pls. refer to pci express specs for -other fields. +Ratelimits are exposed in the form of sysfs attributes and configurable. +See Documentation/ABI/testing/sysfs-bus-pci-devices-aer. 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 +Documentation/ABI/testing/sysfs-bus-pci-devices-aer. Developer Guide =============== -To enable AER aware support requires a software driver to configure -the AER capability structure within its device and to provide callbacks. +To enable error recovery, a software driver must provide callbacks. -To support AER better, developers need understand how AER does work -firstly. +To support AER better, developers need to understand how AER works. -PCI Express errors are classified into two types: correctable errors -and uncorrectable errors. This classification is based on the impacts +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 PCI Express protocol can recover without any software +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 +corrected by hardware. + +Unlike correctable errors, uncorrectable errors impact functionality of the interface. Uncorrectable errors -can cause a particular transaction or a particular PCI Express link +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 PCI Express link itself is fully functional. Fatal errors, on +but the PCIe link itself is fully functional. Fatal errors, on the other hand, cause the link to be unreliable. -When AER is enabled, a PCI Express device will automatically send an -error message to the PCIe root port above it when the device captures +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 PCI Express -capability structure. Error information being logged includes storing -the error reporting agent's requestor ID into the Error Source +internally processes and logs the error message in its AER +Capability structure. Error information being logged includes storing +the error reporting agent's Requester 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 Root -Error Command Register, the Root Port generates an interrupt if an +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 PCI Express +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. -Configure the AER capability structure --------------------------------------- - -AER aware drivers of PCI Express component need change the device -control registers to enable AER. They also could change AER registers, -including mask and severity registers. Helper function -pci_enable_pcie_error_reporting could be used to enable AER. See -section 3.3. - Provide callbacks ----------------- -callback reset_link to reset pci express link -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -This callback is used to reset the pci express 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 pci express link, so all -upstream ports should 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 PCI Express AER Root driver uses error callbacks to coordinate +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. AER driver follows the rules defined in -pci-error-recovery.txt except pci express specific parts (e.g. -reset_link). Pls. refer to pci-error-recovery.txt for detailed +pointers. The AER driver follows the rules defined in +pci-error-recovery.rst except PCIe-specific parts (see +below). Please refer to pci-error-recovery.rst for detailed definitions of the callbacks. -Below sections specify when to call the error callback functions. +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 PCI Express protocol can recover without any +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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Uncorrectable (non-fatal and fatal) errors +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The AER driver performs a Secondary Bus Reset to recover from +uncorrectable errors. The reset is applied at the port above +the originating device: If the originating device is an Endpoint, +only the Endpoint is reset. If on the other hand the originating +device has subordinate devices, those are all affected by the +reset as well. + +If the originating device is a Root Complex Integrated Endpoint, +there's no port above where a Secondary Bus Reset could be applied. +In this case, the AER driver instead applies a Function Level Reset. -If an error message indicates a non-fatal error, performing link reset +If an error message indicates a non-fatal error, performing a 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:: +question. For example:: - EndPoint<==>DownstreamPort B<==>UpstreamPort A<==>RootPort + 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. +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. +whether it can recover without a reset, considers the device unrecoverable +or needs a reset for recovery. If all affected drivers agree that they can +recover without a reset, it is skipped. Should one driver request a reset, +it overrides all other drivers. 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. - -helper functions ----------------- -:: - - int pci_enable_pcie_error_reporting(struct pci_dev *dev); - -pci_enable_pcie_error_reporting enables the device to send error -messages to root port when an error is detected. Note that devices -don't enable the error reporting by default, so device drivers need -call this function to enable it. - -:: +a hierarchy in question. Then, performing a reset at upstream is +necessary. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER +to indicate that recovery without a reset is possible, the error +handling goes to mmio_enabled, but afterwards a reset is still +performed. - int pci_disable_pcie_error_reporting(struct pci_dev *dev); +In other words, for non-fatal errors, drivers may opt in to a reset. +But for fatal errors, they cannot opt out of a reset, based on the +assumption that the link is unreliable. -pci_disable_pcie_error_reporting disables the device to send error -messages to root port when an error is detected. - -:: - - int pci_aer_clear_nonfatal_status(struct pci_dev *dev);` - -pci_aer_clear_nonfatal_status clears non-fatal errors in the uncorrectable -error status register. - -Frequent Asked Questions ------------------------- +Frequently Asked Questions +-------------------------- Q: - What happens if a PCI Express device driver does not provide an + 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. - -Q: - How does this infrastructure deal with driver that is not PCI - Express aware? - -A: - This infrastructure calls the error callback functions of the - driver when an error happens. But if the driver is not aware of - PCI Express, the device might not report its own errors to root - port. - -Q: - What modifications will that driver need to make it compatible - with the PCI Express AER Root driver? - -A: - It could call the helper functions to enable AER in devices and - cleanup uncorrectable status register. Pls. refer to section 3.3. + The devices attached with the driver won't be recovered. + The kernel will print out informational messages to identify + unrecoverable devices. Software error injection @@ -294,7 +251,7 @@ After reboot with new kernel or insert the module, a device file named Then, you need a user space tool named aer-inject, which can be gotten from: - https://git.kernel.org/cgit/linux/kernel/git/gong.chen/aer-inject.git/ + https://github.com/intel/aer-inject.git -More information about aer-inject can be found in the document comes -with its source code. +More information about aer-inject can be found in the document in +its source code. |