Based on kernel version 2.6.25. Page generated on 2008-04-18 21:22 EST.
1 The PCI Express Advanced Error Reporting Driver Guide HOWTO 2 T. Long Nguyen <tom.l.nguyen[AT]intel[DOT]com> 3 Yanmin Zhang <yanmin.zhang[AT]intel[DOT]com> 4 07/29/2006 5 6 7 1. Overview 8 9 1.1 About this guide 10 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. 15 16 1.2 Copyright © Intel Corporation 2006. 17 18 1.3 What is the PCI Express AER Driver? 19 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. 28 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: 32 33 - Gathers the comprehensive error information if errors occurred. 34 - Reports error to the users. 35 - Performs error recovery actions. 36 37 AER driver only attaches root ports which support PCI-Express AER 38 capability. 39 40 41 2. User Guide 42 43 2.1 Include the PCI Express AER Root Driver into the Linux Kernel 44 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 49 CONFIG_PCIEAER = y. 50 51 2.2 Load PCI Express AER Root Driver 52 There is a case where a system has AER support in BIOS. Enabling the AER 53 Root driver and having AER support in BIOS may result unpredictable 54 behavior. To avoid this conflict, a successful load of the AER Root driver 55 requires ACPI _OSC support in the BIOS to allow the AER Root driver to 56 request for native control of AER. See the PCI FW 3.0 Specification for 57 details regarding OSC usage. Currently, lots of firmwares don't provide 58 _OSC support while they use PCI Express. To support such firmwares, 59 forceload, a parameter of type bool, could enable AER to continue to 60 be initiated although firmwares have no _OSC support. To enable the 61 walkaround, pls. add aerdriver.forceload=y to kernel boot parameter line 62 when booting kernel. Note that forceload=n by default. 63 64 2.3 AER error output 65 When a PCI-E AER error is captured, an error message will be outputed to 66 console. If it's a correctable error, it is outputed as a warning. 67 Otherwise, it is printed as an error. So users could choose different 68 log level to filter out correctable error messages. 69 70 Below shows an example. 71 +------ PCI-Express Device Error -----+ 72 Error Severity : Uncorrected (Fatal) 73 PCIE Bus Error type : Transaction Layer 74 Unsupported Request : First 75 Requester ID : 0500 76 VendorID=8086h, DeviceID=0329h, Bus=05h, Device=00h, Function=00h 77 TLB Header: 78 04000001 00200a03 05010000 00050100 79 80 In the example, 'Requester ID' means the ID of the device who sends 81 the error message to root port. Pls. refer to pci express specs for 82 other fields. 83 84 85 3. Developer Guide 86 87 To enable AER aware support requires a software driver to configure 88 the AER capability structure within its device and to provide callbacks. 89 90 To support AER better, developers need understand how AER does work 91 firstly. 92 93 PCI Express errors are classified into two types: correctable errors 94 and uncorrectable errors. This classification is based on the impacts 95 of those errors, which may result in degraded performance or function 96 failure. 97 98 Correctable errors pose no impacts on the functionality of the 99 interface. The PCI Express protocol can recover without any software 100 intervention or any loss of data. These errors are detected and 101 corrected by hardware. Unlike correctable errors, uncorrectable 102 errors impact functionality of the interface. Uncorrectable errors 103 can cause a particular transaction or a particular PCI Express link 104 to be unreliable. Depending on those error conditions, uncorrectable 105 errors are further classified into non-fatal errors and fatal errors. 106 Non-fatal errors cause the particular transaction to be unreliable, 107 but the PCI Express link itself is fully functional. Fatal errors, on 108 the other hand, cause the link to be unreliable. 109 110 When AER is enabled, a PCI Express device will automatically send an 111 error message to the PCIE root port above it when the device captures 112 an error. The Root Port, upon receiving an error reporting message, 113 internally processes and logs the error message in its PCI Express 114 capability structure. Error information being logged includes storing 115 the error reporting agent's requestor ID into the Error Source 116 Identification Registers and setting the error bits of the Root Error 117 Status Register accordingly. If AER error reporting is enabled in Root 118 Error Command Register, the Root Port generates an interrupt if an 119 error is detected. 120 121 Note that the errors as described above are related to the PCI Express 122 hierarchy and links. These errors do not include any device specific 123 errors because device specific errors will still get sent directly to 124 the device driver. 125 126 3.1 Configure the AER capability structure 127 128 AER aware drivers of PCI Express component need change the device 129 control registers to enable AER. They also could change AER registers, 130 including mask and severity registers. Helper function 131 pci_enable_pcie_error_reporting could be used to enable AER. See 132 section 3.3. 133 134 3.2. Provide callbacks 135 136 3.2.1 callback reset_link to reset pci express link 137 138 This callback is used to reset the pci express physical link when a 139 fatal error happens. The root port aer service driver provides a 140 default reset_link function, but different upstream ports might 141 have different specifications to reset pci express link, so all 142 upstream ports should provide their own reset_link functions. 143 144 In struct pcie_port_service_driver, a new pointer, reset_link, is 145 added. 146 147 pci_ers_result_t (*reset_link) (struct pci_dev *dev); 148 149 Section 3.2.2.2 provides more detailed info on when to call 150 reset_link. 151 152 3.2.2 PCI error-recovery callbacks 153 154 The PCI Express AER Root driver uses error callbacks to coordinate 155 with downstream device drivers associated with a hierarchy in question 156 when performing error recovery actions. 157 158 Data struct pci_driver has a pointer, err_handler, to point to 159 pci_error_handlers who consists of a couple of callback function 160 pointers. AER driver follows the rules defined in 161 pci-error-recovery.txt except pci express specific parts (e.g. 162 reset_link). Pls. refer to pci-error-recovery.txt for detailed 163 definitions of the callbacks. 164 165 Below sections specify when to call the error callback functions. 166 167 3.2.2.1 Correctable errors 168 169 Correctable errors pose no impacts on the functionality of 170 the interface. The PCI Express protocol can recover without any 171 software intervention or any loss of data. These errors do not 172 require any recovery actions. The AER driver clears the device's 173 correctable error status register accordingly and logs these errors. 174 175 3.2.2.2 Non-correctable (non-fatal and fatal) errors 176 177 If an error message indicates a non-fatal error, performing link reset 178 at upstream is not required. The AER driver calls error_detected(dev, 179 pci_channel_io_normal) to all drivers associated within a hierarchy in 180 question. for example, 181 EndPoint<==>DownstreamPort B<==>UpstreamPort A<==>RootPort. 182 If Upstream port A captures an AER error, the hierarchy consists of 183 Downstream port B and EndPoint. 184 185 A driver may return PCI_ERS_RESULT_CAN_RECOVER, 186 PCI_ERS_RESULT_DISCONNECT, or PCI_ERS_RESULT_NEED_RESET, depending on 187 whether it can recover or the AER driver calls mmio_enabled as next. 188 189 If an error message indicates a fatal error, kernel will broadcast 190 error_detected(dev, pci_channel_io_frozen) to all drivers within 191 a hierarchy in question. Then, performing link reset at upstream is 192 necessary. As different kinds of devices might use different approaches 193 to reset link, AER port service driver is required to provide the 194 function to reset link. Firstly, kernel looks for if the upstream 195 component has an aer driver. If it has, kernel uses the reset_link 196 callback of the aer driver. If the upstream component has no aer driver 197 and the port is downstream port, we will use the aer driver of the 198 root port who reports the AER error. As for upstream ports, 199 they should provide their own aer service drivers with reset_link 200 function. If error_detected returns PCI_ERS_RESULT_CAN_RECOVER and 201 reset_link returns PCI_ERS_RESULT_RECOVERED, the error handling goes 202 to mmio_enabled. 203 204 3.3 helper functions 205 206 3.3.1 int pci_find_aer_capability(struct pci_dev *dev); 207 pci_find_aer_capability locates the PCI Express AER capability 208 in the device configuration space. If the device doesn't support 209 PCI-Express AER, the function returns 0. 210 211 3.3.2 int pci_enable_pcie_error_reporting(struct pci_dev *dev); 212 pci_enable_pcie_error_reporting enables the device to send error 213 messages to root port when an error is detected. Note that devices 214 don't enable the error reporting by default, so device drivers need 215 call this function to enable it. 216 217 3.3.3 int pci_disable_pcie_error_reporting(struct pci_dev *dev); 218 pci_disable_pcie_error_reporting disables the device to send error 219 messages to root port when an error is detected. 220 221 3.3.4 int pci_cleanup_aer_uncorrect_error_status(struct pci_dev *dev); 222 pci_cleanup_aer_uncorrect_error_status cleanups the uncorrectable 223 error status register. 224 225 3.4 Frequent Asked Questions 226 227 Q: What happens if a PCI Express device driver does not provide an 228 error recovery handler (pci_driver->err_handler is equal to NULL)? 229 230 A: The devices attached with the driver won't be recovered. If the 231 error is fatal, kernel will print out warning messages. Please refer 232 to section 3 for more information. 233 234 Q: What happens if an upstream port service driver does not provide 235 callback reset_link? 236 237 A: Fatal error recovery will fail if the errors are reported by the 238 upstream ports who are attached by the service driver. 239 240 Q: How does this infrastructure deal with driver that is not PCI 241 Express aware? 242 243 A: This infrastructure calls the error callback functions of the 244 driver when an error happens. But if the driver is not aware of 245 PCI Express, the device might not report its own errors to root 246 port. 247 248 Q: What modifications will that driver need to make it compatible 249 with the PCI Express AER Root driver? 250 251 A: It could call the helper functions to enable AER in devices and 252 cleanup uncorrectable status register. Pls. refer to section 3.3.
