Documentation: PCI: convert pcieaer-howto.txt to reST

Convert plain text documentation to reStructuredText format and add it to
Sphinx TOC tree.  No essential content change.

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

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-   The PCI Express Advanced Error Reporting Driver Guide HOWTO
-		T. Long Nguyen	<tom.l.nguyen@intel.com>
-		Yanmin Zhang	<yanmin.zhang@intel.com>
-				07/29/2006
-
-
-1. Overview
-
-1.1 About this guide
-
-This guide describes the basics of the PCI Express 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.
-
-1.2 Copyright (C) Intel Corporation 2006.
-
-1.3 What is the PCI Express 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
-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
-set of error reporting requirements. Advanced Error Reporting
-capability is implemented with a PCI Express 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:
-
--	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.
-
-
-2. User Guide
-
-2.1 Include the PCI Express 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.
-
-2.2 Load PCI Express 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
-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
-Specification for details regarding _OSC usage.
-
-2.3 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.
-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 who sends
-the error message to root port. Pls. refer to pci express specs for
-other fields.
-
-2.4 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
-
-3. 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 support AER better, developers need understand how AER does work
-firstly.
-
-PCI Express errors are classified into two types: correctable errors
-and uncorrectable errors. This classification is based on the impacts
-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
-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 PCI Express 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
-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
-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
-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
-error is detected.
-
-Note that the errors as described above are related to the PCI Express
-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.
-
-3.1 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.
-
-3.2. Provide callbacks
-
-3.2.1 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.
-
-In struct pcie_port_service_driver, a new pointer, reset_link, is
-added.
-
-pci_ers_result_t (*reset_link) (struct pci_dev *dev);
-
-Section 3.2.2.2 provides more detailed info on when to call
-reset_link.
-
-3.2.2 PCI error-recovery callbacks
-
-The PCI Express 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
-definitions of the callbacks.
-
-Below sections specify when to call the error callback functions.
-
-3.2.2.1 Correctable errors
-
-Correctable errors pose no impacts on the functionality of
-the interface. The PCI Express 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.
-
-3.2.2.2 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<==>DownstreamPort B<==>UpstreamPort A<==>RootPort.
-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. Firstly, kernel looks for if the upstream
-component has an aer driver. If it has, kernel uses the reset_link
-callback of the aer driver. If the upstream component has no aer driver
-and the port is downstream port, we will perform a hot reset as the
-default by setting the Secondary Bus Reset bit of the Bridge Control
-register associated with the downstream port. As for upstream ports,
-they should provide their own aer service drivers with reset_link
-function. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER and
-reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes
-to mmio_enabled.
-
-3.3 helper functions
-
-3.3.1 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.
-
-3.3.2 int pci_disable_pcie_error_reporting(struct pci_dev *dev);
-pci_disable_pcie_error_reporting disables the device to send error
-messages to root port when an error is detected.
-
-3.3.3 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev);
-pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable
-error status register.
-
-3.4 Frequent Asked Questions
-
-Q: What happens if a PCI Express 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.
-
-
-4. 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://git.kernel.org/cgit/linux/kernel/git/gong.chen/aer-inject.git/
-
-More information about aer-inject can be found in the document comes
-with its source code.