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 5 6 71. Overview 8 91.1 About this guide 10 11This guide describes the basics of the PCI Express Advanced Error 12Reporting (AER) driver and provides information on how to use it, as 13well as how to enable the drivers of endpoint devices to conform with 14PCI Express AER driver. 15 161.2 Copyright (C) Intel Corporation 2006. 17 181.3 What is the PCI Express AER Driver? 19 20PCI Express error signaling can occur on the PCI Express link itself 21or on behalf of transactions initiated on the link. PCI Express 22defines two error reporting paradigms: the baseline capability and 23the Advanced Error Reporting capability. The baseline capability is 24required of all PCI Express components providing a minimum defined 25set of error reporting requirements. Advanced Error Reporting 26capability is implemented with a PCI Express advanced error reporting 27extended capability structure providing more robust error reporting. 28 29The PCI Express AER driver provides the infrastructure to support PCI 30Express Advanced Error Reporting capability. The PCI Express AER 31driver provides three basic functions: 32 33- Gathers the comprehensive error information if errors occurred. 34- Reports error to the users. 35- Performs error recovery actions. 36 37AER driver only attaches root ports which support PCI-Express AER 38capability. 39 40 412. User Guide 42 432.1 Include the PCI Express AER Root Driver into the Linux Kernel 44 45The PCI Express AER Root driver is a Root Port service driver attached 46to the PCI Express Port Bus driver. If a user wants to use it, the driver 47has to be compiled. Option CONFIG_PCIEAER supports this capability. It 48depends on CONFIG_PCIEPORTBUS, so pls. set CONFIG_PCIEPORTBUS=y and 49CONFIG_PCIEAER = y. 50 512.2 Load PCI Express AER Root Driver 52There is a case where a system has AER support in BIOS. Enabling the AER 53Root driver and having AER support in BIOS may result unpredictable 54behavior. To avoid this conflict, a successful load of the AER Root driver 55requires ACPI _OSC support in the BIOS to allow the AER Root driver to 56request for native control of AER. See the PCI FW 3.0 Specification for 57details regarding OSC usage. Currently, lots of firmwares don't provide 58_OSC support while they use PCI Express. To support such firmwares, 59forceload, a parameter of type bool, could enable AER to continue to 60be initiated although firmwares have no _OSC support. To enable the 61walkaround, pls. add aerdriver.forceload=y to kernel boot parameter line 62when booting kernel. Note that forceload=n by default. 63 64nosourceid, another parameter of type bool, can be used when broken 65hardware (mostly chipsets) has root ports that cannot obtain the reporting 66source ID. nosourceid=n by default. 67 682.3 AER error output 69When a PCI-E AER error is captured, an error message will be outputted to 70console. If it's a correctable error, it is outputted as a warning. 71Otherwise, it is printed as an error. So users could choose different 72log level to filter out correctable error messages. 73 74Below shows an example: 750000:50:00.0: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, id=0500(Requester ID) 760000:50:00.0: device [8086:0329] error status/mask=00100000/00000000 770000:50:00.0: [20] Unsupported Request (First) 780000:50:00.0: TLP Header: 04000001 00200a03 05010000 00050100 79 80In the example, 'Requester ID' means the ID of the device who sends 81the error message to root port. Pls. refer to pci express specs for 82other fields. 83 84 853. Developer Guide 86 87To enable AER aware support requires a software driver to configure 88the AER capability structure within its device and to provide callbacks. 89 90To support AER better, developers need understand how AER does work 91firstly. 92 93PCI Express errors are classified into two types: correctable errors 94and uncorrectable errors. This classification is based on the impacts 95of those errors, which may result in degraded performance or function 96failure. 97 98Correctable errors pose no impacts on the functionality of the 99interface. The PCI Express protocol can recover without any software 100intervention or any loss of data. These errors are detected and 101corrected by hardware. Unlike correctable errors, uncorrectable 102errors impact functionality of the interface. Uncorrectable errors 103can cause a particular transaction or a particular PCI Express link 104to be unreliable. Depending on those error conditions, uncorrectable 105errors are further classified into non-fatal errors and fatal errors. 106Non-fatal errors cause the particular transaction to be unreliable, 107but the PCI Express link itself is fully functional. Fatal errors, on 108the other hand, cause the link to be unreliable. 109 110When AER is enabled, a PCI Express device will automatically send an 111error message to the PCIe root port above it when the device captures 112an error. The Root Port, upon receiving an error reporting message, 113internally processes and logs the error message in its PCI Express 114capability structure. Error information being logged includes storing 115the error reporting agent's requestor ID into the Error Source 116Identification Registers and setting the error bits of the Root Error 117Status Register accordingly. If AER error reporting is enabled in Root 118Error Command Register, the Root Port generates an interrupt if an 119error is detected. 120 121Note that the errors as described above are related to the PCI Express 122hierarchy and links. These errors do not include any device specific 123errors because device specific errors will still get sent directly to 124the device driver. 125 1263.1 Configure the AER capability structure 127 128AER aware drivers of PCI Express component need change the device 129control registers to enable AER. They also could change AER registers, 130including mask and severity registers. Helper function 131pci_enable_pcie_error_reporting could be used to enable AER. See 132section 3.3. 133 1343.2. Provide callbacks 135 1363.2.1 callback reset_link to reset pci express link 137 138This callback is used to reset the pci express physical link when a 139fatal error happens. The root port aer service driver provides a 140default reset_link function, but different upstream ports might 141have different specifications to reset pci express link, so all 142upstream ports should provide their own reset_link functions. 143 144In struct pcie_port_service_driver, a new pointer, reset_link, is 145added. 146 147pci_ers_result_t (*reset_link) (struct pci_dev *dev); 148 149Section 3.2.2.2 provides more detailed info on when to call 150reset_link. 151 1523.2.2 PCI error-recovery callbacks 153 154The PCI Express AER Root driver uses error callbacks to coordinate 155with downstream device drivers associated with a hierarchy in question 156when performing error recovery actions. 157 158Data struct pci_driver has a pointer, err_handler, to point to 159pci_error_handlers who consists of a couple of callback function 160pointers. AER driver follows the rules defined in 161pci-error-recovery.txt except pci express specific parts (e.g. 162reset_link). Pls. refer to pci-error-recovery.txt for detailed 163definitions of the callbacks. 164 165Below sections specify when to call the error callback functions. 166 1673.2.2.1 Correctable errors 168 169Correctable errors pose no impacts on the functionality of 170the interface. The PCI Express protocol can recover without any 171software intervention or any loss of data. These errors do not 172require any recovery actions. The AER driver clears the device's 173correctable error status register accordingly and logs these errors. 174 1753.2.2.2 Non-correctable (non-fatal and fatal) errors 176 177If an error message indicates a non-fatal error, performing link reset 178at upstream is not required. The AER driver calls error_detected(dev, 179pci_channel_io_normal) to all drivers associated within a hierarchy in 180question. for example, 181EndPoint<==>DownstreamPort B<==>UpstreamPort A<==>RootPort. 182If Upstream port A captures an AER error, the hierarchy consists of 183Downstream port B and EndPoint. 184 185A driver may return PCI_ERS_RESULT_CAN_RECOVER, 186PCI_ERS_RESULT_DISCONNECT, or PCI_ERS_RESULT_NEED_RESET, depending on 187whether it can recover or the AER driver calls mmio_enabled as next. 188 189If an error message indicates a fatal error, kernel will broadcast 190error_detected(dev, pci_channel_io_frozen) to all drivers within 191a hierarchy in question. Then, performing link reset at upstream is 192necessary. As different kinds of devices might use different approaches 193to reset link, AER port service driver is required to provide the 194function to reset link. Firstly, kernel looks for if the upstream 195component has an aer driver. If it has, kernel uses the reset_link 196callback of the aer driver. If the upstream component has no aer driver 197and the port is downstream port, we will perform a hot reset as the 198default by setting the Secondary Bus Reset bit of the Bridge Control 199register associated with the downstream port. As for upstream ports, 200they should provide their own aer service drivers with reset_link 201function. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER and 202reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes 203to mmio_enabled. 204 2053.3 helper functions 206 2073.3.1 int pci_enable_pcie_error_reporting(struct pci_dev *dev); 208pci_enable_pcie_error_reporting enables the device to send error 209messages to root port when an error is detected. Note that devices 210don't enable the error reporting by default, so device drivers need 211call this function to enable it. 212 2133.3.2 int pci_disable_pcie_error_reporting(struct pci_dev *dev); 214pci_disable_pcie_error_reporting disables the device to send error 215messages to root port when an error is detected. 216 2173.3.3 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev); 218pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable 219error status register. 220 2213.4 Frequent Asked Questions 222 223Q: What happens if a PCI Express device driver does not provide an 224error recovery handler (pci_driver->err_handler is equal to NULL)? 225 226A: The devices attached with the driver won't be recovered. If the 227error is fatal, kernel will print out warning messages. Please refer 228to section 3 for more information. 229 230Q: What happens if an upstream port service driver does not provide 231callback reset_link? 232 233A: Fatal error recovery will fail if the errors are reported by the 234upstream ports who are attached by the service driver. 235 236Q: How does this infrastructure deal with driver that is not PCI 237Express aware? 238 239A: This infrastructure calls the error callback functions of the 240driver when an error happens. But if the driver is not aware of 241PCI Express, the device might not report its own errors to root 242port. 243 244Q: What modifications will that driver need to make it compatible 245with the PCI Express AER Root driver? 246 247A: It could call the helper functions to enable AER in devices and 248cleanup uncorrectable status register. Pls. refer to section 3.3. 249 250 2514. Software error injection 252 253Debugging PCIe AER error recovery code is quite difficult because it 254is hard to trigger real hardware errors. Software based error 255injection can be used to fake various kinds of PCIe errors. 256 257First you should enable PCIe AER software error injection in kernel 258configuration, that is, following item should be in your .config. 259 260CONFIG_PCIEAER_INJECT=y or CONFIG_PCIEAER_INJECT=m 261 262After reboot with new kernel or insert the module, a device file named 263/dev/aer_inject should be created. 264 265Then, you need a user space tool named aer-inject, which can be gotten 266from: 267 http://www.kernel.org/pub/linux/utils/pci/aer-inject/ 268 269More information about aer-inject can be found in the document comes 270with its source code. 271