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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	   The PCI Express Advanced Error Reporting Driver Guide HOWTO
2			T. Long Nguyen	<tom.l.nguyen@intel.com>
3			Yanmin Zhang	<yanmin.zhang@intel.com>
4					07/29/2006
7	1. Overview
9	1.1 About this guide
11	This guide describes the basics of the PCI Express Advanced Error
12	Reporting (AER) driver and provides information on how to use it, as
13	well as how to enable the drivers of endpoint devices to conform with
14	PCI Express AER driver.
16	1.2 Copyright (C) Intel Corporation 2006.
18	1.3 What is the PCI Express AER Driver?
20	PCI Express error signaling can occur on the PCI Express link itself
21	or on behalf of transactions initiated on the link. PCI Express
22	defines two error reporting paradigms: the baseline capability and
23	the Advanced Error Reporting capability. The baseline capability is
24	required of all PCI Express components providing a minimum defined
25	set of error reporting requirements. Advanced Error Reporting
26	capability is implemented with a PCI Express advanced error reporting
27	extended capability structure providing more robust error reporting.
29	The PCI Express AER driver provides the infrastructure to support PCI
30	Express Advanced Error Reporting capability. The PCI Express AER
31	driver provides three basic functions:
33	-	Gathers the comprehensive error information if errors occurred.
34	-	Reports error to the users.
35	-	Performs error recovery actions.
37	AER driver only attaches root ports which support PCI-Express AER
38	capability.
41	2. User Guide
43	2.1 Include the PCI Express AER Root Driver into the Linux Kernel
45	The PCI Express AER Root driver is a Root Port service driver attached
46	to the PCI Express Port Bus driver. If a user wants to use it, the driver
47	has to be compiled. Option CONFIG_PCIEAER supports this capability. It
48	depends on CONFIG_PCIEPORTBUS, so pls. set CONFIG_PCIEPORTBUS=y and
51	2.2 Load PCI Express AER Root Driver
53	Some systems have AER support in firmware. Enabling Linux AER support at
54	the same time the firmware handles AER may result in unpredictable
55	behavior. Therefore, Linux does not handle AER events unless the firmware
56	grants AER control to the OS via the ACPI _OSC method. See the PCI FW 3.0
57	Specification for details regarding _OSC usage.
59	2.3 AER error output
61	When a PCIe AER error is captured, an error message will be output to
62	console. If it's a correctable error, it is output as a warning.
63	Otherwise, it is printed as an error. So users could choose different
64	log level to filter out correctable error messages.
66	Below shows an example:
67	0000:50:00.0: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, id=0500(Requester ID)
68	0000:50:00.0:   device [8086:0329] error status/mask=00100000/00000000
69	0000:50:00.0:    [20] Unsupported Request    (First)
70	0000:50:00.0:   TLP Header: 04000001 00200a03 05010000 00050100
72	In the example, 'Requester ID' means the ID of the device who sends
73	the error message to root port. Pls. refer to pci express specs for
74	other fields.
77	3. Developer Guide
79	To enable AER aware support requires a software driver to configure
80	the AER capability structure within its device and to provide callbacks.
82	To support AER better, developers need understand how AER does work
83	firstly.
85	PCI Express errors are classified into two types: correctable errors
86	and uncorrectable errors. This classification is based on the impacts
87	of those errors, which may result in degraded performance or function
88	failure.
90	Correctable errors pose no impacts on the functionality of the
91	interface. The PCI Express protocol can recover without any software
92	intervention or any loss of data. These errors are detected and
93	corrected by hardware. Unlike correctable errors, uncorrectable
94	errors impact functionality of the interface. Uncorrectable errors
95	can cause a particular transaction or a particular PCI Express link
96	to be unreliable. Depending on those error conditions, uncorrectable
97	errors are further classified into non-fatal errors and fatal errors.
98	Non-fatal errors cause the particular transaction to be unreliable,
99	but the PCI Express link itself is fully functional. Fatal errors, on
100	the other hand, cause the link to be unreliable.
102	When AER is enabled, a PCI Express device will automatically send an
103	error message to the PCIe root port above it when the device captures
104	an error. The Root Port, upon receiving an error reporting message,
105	internally processes and logs the error message in its PCI Express
106	capability structure. Error information being logged includes storing
107	the error reporting agent's requestor ID into the Error Source
108	Identification Registers and setting the error bits of the Root Error
109	Status Register accordingly. If AER error reporting is enabled in Root
110	Error Command Register, the Root Port generates an interrupt if an
111	error is detected.
113	Note that the errors as described above are related to the PCI Express
114	hierarchy and links. These errors do not include any device specific
115	errors because device specific errors will still get sent directly to
116	the device driver.
118	3.1 Configure the AER capability structure
120	AER aware drivers of PCI Express component need change the device
121	control registers to enable AER. They also could change AER registers,
122	including mask and severity registers. Helper function
123	pci_enable_pcie_error_reporting could be used to enable AER. See
124	section 3.3.
126	3.2. Provide callbacks
128	3.2.1 callback reset_link to reset pci express link
130	This callback is used to reset the pci express physical link when a
131	fatal error happens. The root port aer service driver provides a
132	default reset_link function, but different upstream ports might
133	have different specifications to reset pci express link, so all
134	upstream ports should provide their own reset_link functions.
136	In struct pcie_port_service_driver, a new pointer, reset_link, is
137	added.
139	pci_ers_result_t (*reset_link) (struct pci_dev *dev);
141	Section provides more detailed info on when to call
142	reset_link.
144	3.2.2 PCI error-recovery callbacks
146	The PCI Express AER Root driver uses error callbacks to coordinate
147	with downstream device drivers associated with a hierarchy in question
148	when performing error recovery actions.
150	Data struct pci_driver has a pointer, err_handler, to point to
151	pci_error_handlers who consists of a couple of callback function
152	pointers. AER driver follows the rules defined in
153	pci-error-recovery.txt except pci express specific parts (e.g.
154	reset_link). Pls. refer to pci-error-recovery.txt for detailed
155	definitions of the callbacks.
157	Below sections specify when to call the error callback functions.
159 Correctable errors
161	Correctable errors pose no impacts on the functionality of
162	the interface. The PCI Express protocol can recover without any
163	software intervention or any loss of data. These errors do not
164	require any recovery actions. The AER driver clears the device's
165	correctable error status register accordingly and logs these errors.
167 Non-correctable (non-fatal and fatal) errors
169	If an error message indicates a non-fatal error, performing link reset
170	at upstream is not required. The AER driver calls error_detected(dev,
171	pci_channel_io_normal) to all drivers associated within a hierarchy in
172	question. for example,
173	EndPoint<==>DownstreamPort B<==>UpstreamPort A<==>RootPort.
174	If Upstream port A captures an AER error, the hierarchy consists of
175	Downstream port B and EndPoint.
177	A driver may return PCI_ERS_RESULT_CAN_RECOVER,
179	whether it can recover or the AER driver calls mmio_enabled as next.
181	If an error message indicates a fatal error, kernel will broadcast
182	error_detected(dev, pci_channel_io_frozen) to all drivers within
183	a hierarchy in question. Then, performing link reset at upstream is
184	necessary. As different kinds of devices might use different approaches
185	to reset link, AER port service driver is required to provide the
186	function to reset link. Firstly, kernel looks for if the upstream
187	component has an aer driver. If it has, kernel uses the reset_link
188	callback of the aer driver. If the upstream component has no aer driver
189	and the port is downstream port, we will perform a hot reset as the
190	default by setting the Secondary Bus Reset bit of the Bridge Control
191	register associated with the downstream port. As for upstream ports,
192	they should provide their own aer service drivers with reset_link
193	function. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER and
194	reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes
195	to mmio_enabled.
197	3.3 helper functions
199	3.3.1 int pci_enable_pcie_error_reporting(struct pci_dev *dev);
200	pci_enable_pcie_error_reporting enables the device to send error
201	messages to root port when an error is detected. Note that devices
202	don't enable the error reporting by default, so device drivers need
203	call this function to enable it.
205	3.3.2 int pci_disable_pcie_error_reporting(struct pci_dev *dev);
206	pci_disable_pcie_error_reporting disables the device to send error
207	messages to root port when an error is detected.
209	3.3.3 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev);
210	pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable
211	error status register.
213	3.4 Frequent Asked Questions
215	Q: What happens if a PCI Express device driver does not provide an
216	error recovery handler (pci_driver->err_handler is equal to NULL)?
218	A: The devices attached with the driver won't be recovered. If the
219	error is fatal, kernel will print out warning messages. Please refer
220	to section 3 for more information.
222	Q: What happens if an upstream port service driver does not provide
223	callback reset_link?
225	A: Fatal error recovery will fail if the errors are reported by the
226	upstream ports who are attached by the service driver.
228	Q: How does this infrastructure deal with driver that is not PCI
229	Express aware?
231	A: This infrastructure calls the error callback functions of the
232	driver when an error happens. But if the driver is not aware of
233	PCI Express, the device might not report its own errors to root
234	port.
236	Q: What modifications will that driver need to make it compatible
237	with the PCI Express AER Root driver?
239	A: It could call the helper functions to enable AER in devices and
240	cleanup uncorrectable status register. Pls. refer to section 3.3.
243	4. Software error injection
245	Debugging PCIe AER error recovery code is quite difficult because it
246	is hard to trigger real hardware errors. Software based error
247	injection can be used to fake various kinds of PCIe errors.
249	First you should enable PCIe AER software error injection in kernel
250	configuration, that is, following item should be in your .config.
254	After reboot with new kernel or insert the module, a device file named
255	/dev/aer_inject should be created.
257	Then, you need a user space tool named aer-inject, which can be gotten
258	from:
259	    https://git.kernel.org/cgit/linux/kernel/git/gong.chen/aer-inject.git/
261	More information about aer-inject can be found in the document comes
262	with its source code.
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