263 строки
11 KiB
Plaintext
263 строки
11 KiB
Plaintext
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.
|
|
|
|
|
|
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:
|
|
http://www.kernel.org/pub/linux/utils/pci/aer-inject/
|
|
|
|
More information about aer-inject can be found in the document comes
|
|
with its source code.
|