]>
Commit | Line | Data |
---|---|---|
065c6359 LV |
1 | |
2 | PCI Error Recovery | |
3 | ------------------ | |
c9ab8b68 LV |
4 | February 2, 2006 |
5 | ||
6 | Current document maintainer: | |
fe14acd4 MM |
7 | Linas Vepstas <linasvepstas@gmail.com> |
8 | updated by Richard Lary <rlary@us.ibm.com> | |
9 | and Mike Mason <mmlnx@us.ibm.com> on 27-Jul-2009 | |
c9ab8b68 LV |
10 | |
11 | ||
12 | Many PCI bus controllers are able to detect a variety of hardware | |
13 | PCI errors on the bus, such as parity errors on the data and address | |
97e4e959 | 14 | buses, as well as SERR and PERR errors. Some of the more advanced |
c9ab8b68 | 15 | chipsets are able to deal with these errors; these include PCI-E chipsets, |
fe14acd4 MM |
16 | and the PCI-host bridges found on IBM Power4, Power5 and Power6-based |
17 | pSeries boxes. A typical action taken is to disconnect the affected device, | |
c9ab8b68 LV |
18 | halting all I/O to it. The goal of a disconnection is to avoid system |
19 | corruption; for example, to halt system memory corruption due to DMA's | |
20 | to "wild" addresses. Typically, a reconnection mechanism is also | |
21 | offered, so that the affected PCI device(s) are reset and put back | |
22 | into working condition. The reset phase requires coordination | |
23 | between the affected device drivers and the PCI controller chip. | |
24 | This document describes a generic API for notifying device drivers | |
25 | of a bus disconnection, and then performing error recovery. | |
26 | This API is currently implemented in the 2.6.16 and later kernels. | |
27 | ||
28 | Reporting and recovery is performed in several steps. First, when | |
29 | a PCI hardware error has resulted in a bus disconnect, that event | |
30 | is reported as soon as possible to all affected device drivers, | |
31 | including multiple instances of a device driver on multi-function | |
32 | cards. This allows device drivers to avoid deadlocking in spinloops, | |
33 | waiting for some i/o-space register to change, when it never will. | |
34 | It also gives the drivers a chance to defer incoming I/O as | |
35 | needed. | |
36 | ||
37 | Next, recovery is performed in several stages. Most of the complexity | |
38 | is forced by the need to handle multi-function devices, that is, | |
39 | devices that have multiple device drivers associated with them. | |
40 | In the first stage, each driver is allowed to indicate what type | |
41 | of reset it desires, the choices being a simple re-enabling of I/O | |
fe14acd4 | 42 | or requesting a slot reset. |
c9ab8b68 | 43 | |
fe14acd4 MM |
44 | If any driver requests a slot reset, that is what will be done. |
45 | ||
46 | After a reset and/or a re-enabling of I/O, all drivers are | |
c9ab8b68 LV |
47 | again notified, so that they may then perform any device setup/config |
48 | that may be required. After these have all completed, a final | |
49 | "resume normal operations" event is sent out. | |
50 | ||
51 | The biggest reason for choosing a kernel-based implementation rather | |
52 | than a user-space implementation was the need to deal with bus | |
53 | disconnects of PCI devices attached to storage media, and, in particular, | |
54 | disconnects from devices holding the root file system. If the root | |
55 | file system is disconnected, a user-space mechanism would have to go | |
56 | through a large number of contortions to complete recovery. Almost all | |
57 | of the current Linux file systems are not tolerant of disconnection | |
58 | from/reconnection to their underlying block device. By contrast, | |
59 | bus errors are easy to manage in the device driver. Indeed, most | |
60 | device drivers already handle very similar recovery procedures; | |
61 | for example, the SCSI-generic layer already provides significant | |
62 | mechanisms for dealing with SCSI bus errors and SCSI bus resets. | |
63 | ||
64 | ||
65 | Detailed Design | |
66 | --------------- | |
67 | Design and implementation details below, based on a chain of | |
68 | public email discussions with Ben Herrenschmidt, circa 5 April 2005. | |
065c6359 LV |
69 | |
70 | The error recovery API support is exposed to the driver in the form of | |
71 | a structure of function pointers pointed to by a new field in struct | |
c9ab8b68 LV |
72 | pci_driver. A driver that fails to provide the structure is "non-aware", |
73 | and the actual recovery steps taken are platform dependent. The | |
74 | arch/powerpc implementation will simulate a PCI hotplug remove/add. | |
065c6359 LV |
75 | |
76 | This structure has the form: | |
065c6359 LV |
77 | struct pci_error_handlers |
78 | { | |
c9ab8b68 | 79 | int (*error_detected)(struct pci_dev *dev, enum pci_channel_state); |
065c6359 | 80 | int (*mmio_enabled)(struct pci_dev *dev); |
065c6359 | 81 | int (*slot_reset)(struct pci_dev *dev); |
c9ab8b68 | 82 | void (*resume)(struct pci_dev *dev); |
065c6359 LV |
83 | }; |
84 | ||
c9ab8b68 LV |
85 | The possible channel states are: |
86 | enum pci_channel_state { | |
87 | pci_channel_io_normal, /* I/O channel is in normal state */ | |
88 | pci_channel_io_frozen, /* I/O to channel is blocked */ | |
89 | pci_channel_io_perm_failure, /* PCI card is dead */ | |
90 | }; | |
91 | ||
92 | Possible return values are: | |
93 | enum pci_ers_result { | |
94 | PCI_ERS_RESULT_NONE, /* no result/none/not supported in device driver */ | |
95 | PCI_ERS_RESULT_CAN_RECOVER, /* Device driver can recover without slot reset */ | |
96 | PCI_ERS_RESULT_NEED_RESET, /* Device driver wants slot to be reset. */ | |
97 | PCI_ERS_RESULT_DISCONNECT, /* Device has completely failed, is unrecoverable */ | |
98 | PCI_ERS_RESULT_RECOVERED, /* Device driver is fully recovered and operational */ | |
99 | }; | |
100 | ||
101 | A driver does not have to implement all of these callbacks; however, | |
102 | if it implements any, it must implement error_detected(). If a callback | |
103 | is not implemented, the corresponding feature is considered unsupported. | |
104 | For example, if mmio_enabled() and resume() aren't there, then it | |
105 | is assumed that the driver is not doing any direct recovery and requires | |
2fd260f0 | 106 | a slot reset. Typically a driver will want to know about |
c9ab8b68 LV |
107 | a slot_reset(). |
108 | ||
109 | The actual steps taken by a platform to recover from a PCI error | |
110 | event will be platform-dependent, but will follow the general | |
111 | sequence described below. | |
112 | ||
113 | STEP 0: Error Event | |
114 | ------------------- | |
fe14acd4 | 115 | A PCI bus error is detected by the PCI hardware. On powerpc, the slot |
c9ab8b68 LV |
116 | is isolated, in that all I/O is blocked: all reads return 0xffffffff, |
117 | all writes are ignored. | |
118 | ||
119 | ||
120 | STEP 1: Notification | |
121 | -------------------- | |
122 | Platform calls the error_detected() callback on every instance of | |
123 | every driver affected by the error. | |
124 | ||
125 | At this point, the device might not be accessible anymore, depending on | |
126 | the platform (the slot will be isolated on powerpc). The driver may | |
127 | already have "noticed" the error because of a failing I/O, but this | |
128 | is the proper "synchronization point", that is, it gives the driver | |
129 | a chance to cleanup, waiting for pending stuff (timers, whatever, etc...) | |
130 | to complete; it can take semaphores, schedule, etc... everything but | |
131 | touch the device. Within this function and after it returns, the driver | |
065c6359 LV |
132 | shouldn't do any new IOs. Called in task context. This is sort of a |
133 | "quiesce" point. See note about interrupts at the end of this doc. | |
134 | ||
c9ab8b68 LV |
135 | All drivers participating in this system must implement this call. |
136 | The driver must return one of the following result codes: | |
137 | - PCI_ERS_RESULT_CAN_RECOVER: | |
138 | Driver returns this if it thinks it might be able to recover | |
065c6359 | 139 | the HW by just banging IOs or if it wants to be given |
c9ab8b68 LV |
140 | a chance to extract some diagnostic information (see |
141 | mmio_enable, below). | |
142 | - PCI_ERS_RESULT_NEED_RESET: | |
fe14acd4 | 143 | Driver returns this if it can't recover without a |
c9ab8b68 LV |
144 | slot reset. |
145 | - PCI_ERS_RESULT_DISCONNECT: | |
146 | Driver returns this if it doesn't want to recover at all. | |
147 | ||
148 | The next step taken will depend on the result codes returned by the | |
149 | drivers. | |
150 | ||
151 | If all drivers on the segment/slot return PCI_ERS_RESULT_CAN_RECOVER, | |
152 | then the platform should re-enable IOs on the slot (or do nothing in | |
153 | particular, if the platform doesn't isolate slots), and recovery | |
154 | proceeds to STEP 2 (MMIO Enable). | |
155 | ||
156 | If any driver requested a slot reset (by returning PCI_ERS_RESULT_NEED_RESET), | |
157 | then recovery proceeds to STEP 4 (Slot Reset). | |
158 | ||
159 | If the platform is unable to recover the slot, the next step | |
160 | is STEP 6 (Permanent Failure). | |
161 | ||
162 | >>> The current powerpc implementation assumes that a device driver will | |
163 | >>> *not* schedule or semaphore in this routine; the current powerpc | |
065c6359 | 164 | >>> implementation uses one kernel thread to notify all devices; |
c9ab8b68 | 165 | >>> thus, if one device sleeps/schedules, all devices are affected. |
065c6359 LV |
166 | >>> Doing better requires complex multi-threaded logic in the error |
167 | >>> recovery implementation (e.g. waiting for all notification threads | |
168 | >>> to "join" before proceeding with recovery.) This seems excessively | |
169 | >>> complex and not worth implementing. | |
170 | ||
c9ab8b68 LV |
171 | >>> The current powerpc implementation doesn't much care if the device |
172 | >>> attempts I/O at this point, or not. I/O's will fail, returning | |
fe14acd4 MM |
173 | >>> a value of 0xff on read, and writes will be dropped. If more than |
174 | >>> EEH_MAX_FAILS I/O's are attempted to a frozen adapter, EEH | |
175 | >>> assumes that the device driver has gone into an infinite loop | |
97e4e959 | 176 | >>> and prints an error to syslog. A reboot is then required to |
fe14acd4 | 177 | >>> get the device working again. |
065c6359 | 178 | |
c9ab8b68 LV |
179 | STEP 2: MMIO Enabled |
180 | ------------------- | |
181 | The platform re-enables MMIO to the device (but typically not the | |
182 | DMA), and then calls the mmio_enabled() callback on all affected | |
183 | device drivers. | |
065c6359 | 184 | |
c9ab8b68 | 185 | This is the "early recovery" call. IOs are allowed again, but DMA is |
fe14acd4 MM |
186 | not, with some restrictions. This is NOT a callback for the driver to |
187 | start operations again, only to peek/poke at the device, extract diagnostic | |
188 | information, if any, and eventually do things like trigger a device local | |
189 | reset or some such, but not restart operations. This callback is made if | |
190 | all drivers on a segment agree that they can try to recover and if no automatic | |
191 | link reset was performed by the HW. If the platform can't just re-enable IOs | |
192 | without a slot reset or a link reset, it will not call this callback, and | |
193 | instead will have gone directly to STEP 3 (Link Reset) or STEP 4 (Slot Reset) | |
c9ab8b68 LV |
194 | |
195 | >>> The following is proposed; no platform implements this yet: | |
196 | >>> Proposal: All I/O's should be done _synchronously_ from within | |
197 | >>> this callback, errors triggered by them will be returned via | |
198 | >>> the normal pci_check_whatever() API, no new error_detected() | |
199 | >>> callback will be issued due to an error happening here. However, | |
200 | >>> such an error might cause IOs to be re-blocked for the whole | |
201 | >>> segment, and thus invalidate the recovery that other devices | |
202 | >>> on the same segment might have done, forcing the whole segment | |
203 | >>> into one of the next states, that is, link reset or slot reset. | |
204 | ||
205 | The driver should return one of the following result codes: | |
206 | - PCI_ERS_RESULT_RECOVERED | |
065c6359 | 207 | Driver returns this if it thinks the device is fully |
c9ab8b68 | 208 | functional and thinks it is ready to start |
065c6359 LV |
209 | normal driver operations again. There is no |
210 | guarantee that the driver will actually be | |
211 | allowed to proceed, as another driver on the | |
212 | same segment might have failed and thus triggered a | |
213 | slot reset on platforms that support it. | |
214 | ||
c9ab8b68 | 215 | - PCI_ERS_RESULT_NEED_RESET |
065c6359 | 216 | Driver returns this if it thinks the device is not |
a33f3224 | 217 | recoverable in its current state and it needs a slot |
065c6359 LV |
218 | reset to proceed. |
219 | ||
c9ab8b68 | 220 | - PCI_ERS_RESULT_DISCONNECT |
065c6359 LV |
221 | Same as above. Total failure, no recovery even after |
222 | reset driver dead. (To be defined more precisely) | |
223 | ||
c9ab8b68 LV |
224 | The next step taken depends on the results returned by the drivers. |
225 | If all drivers returned PCI_ERS_RESULT_RECOVERED, then the platform | |
226 | proceeds to either STEP3 (Link Reset) or to STEP 5 (Resume Operations). | |
227 | ||
228 | If any driver returned PCI_ERS_RESULT_NEED_RESET, then the platform | |
229 | proceeds to STEP 4 (Slot Reset) | |
065c6359 | 230 | |
c9ab8b68 LV |
231 | STEP 3: Link Reset |
232 | ------------------ | |
2fd260f0 | 233 | The platform resets the link. This is a PCI-Express specific step |
97e4e959 | 234 | and is done whenever a fatal error has been detected that can be |
2fd260f0 | 235 | "solved" by resetting the link. |
c9ab8b68 | 236 | |
c9ab8b68 LV |
237 | STEP 4: Slot Reset |
238 | ------------------ | |
c9ab8b68 | 239 | |
fe14acd4 | 240 | In response to a return value of PCI_ERS_RESULT_NEED_RESET, the |
97e4e959 | 241 | the platform will perform a slot reset on the requesting PCI device(s). |
fe14acd4 MM |
242 | The actual steps taken by a platform to perform a slot reset |
243 | will be platform-dependent. Upon completion of slot reset, the | |
244 | platform will call the device slot_reset() callback. | |
245 | ||
246 | Powerpc platforms implement two levels of slot reset: | |
247 | soft reset(default) and fundamental(optional) reset. | |
248 | ||
249 | Powerpc soft reset consists of asserting the adapter #RST line and then | |
c9ab8b68 LV |
250 | restoring the PCI BAR's and PCI configuration header to a state |
251 | that is equivalent to what it would be after a fresh system | |
252 | power-on followed by power-on BIOS/system firmware initialization. | |
fe14acd4 MM |
253 | Soft reset is also known as hot-reset. |
254 | ||
255 | Powerpc fundamental reset is supported by PCI Express cards only | |
256 | and results in device's state machines, hardware logic, port states and | |
257 | configuration registers to initialize to their default conditions. | |
258 | ||
259 | For most PCI devices, a soft reset will be sufficient for recovery. | |
260 | Optional fundamental reset is provided to support a limited number | |
97e4e959 | 261 | of PCI Express devices for which a soft reset is not sufficient |
fe14acd4 MM |
262 | for recovery. |
263 | ||
c9ab8b68 LV |
264 | If the platform supports PCI hotplug, then the reset might be |
265 | performed by toggling the slot electrical power off/on. | |
065c6359 | 266 | |
c9ab8b68 LV |
267 | It is important for the platform to restore the PCI config space |
268 | to the "fresh poweron" state, rather than the "last state". After | |
269 | a slot reset, the device driver will almost always use its standard | |
270 | device initialization routines, and an unusual config space setup | |
271 | may result in hung devices, kernel panics, or silent data corruption. | |
065c6359 | 272 | |
c9ab8b68 LV |
273 | This call gives drivers the chance to re-initialize the hardware |
274 | (re-download firmware, etc.). At this point, the driver may assume | |
fe14acd4 MM |
275 | that the card is in a fresh state and is fully functional. The slot |
276 | is unfrozen and the driver has full access to PCI config space, | |
277 | memory mapped I/O space and DMA. Interrupts (Legacy, MSI, or MSI-X) | |
278 | will also be available. | |
065c6359 | 279 | |
fe14acd4 | 280 | Drivers should not restart normal I/O processing operations |
c9ab8b68 LV |
281 | at this point. If all device drivers report success on this |
282 | callback, the platform will call resume() to complete the sequence, | |
283 | and let the driver restart normal I/O processing. | |
065c6359 LV |
284 | |
285 | A driver can still return a critical failure for this function if | |
286 | it can't get the device operational after reset. If the platform | |
c9ab8b68 | 287 | previously tried a soft reset, it might now try a hard reset (power |
065c6359 LV |
288 | cycle) and then call slot_reset() again. It the device still can't |
289 | be recovered, there is nothing more that can be done; the platform | |
290 | will typically report a "permanent failure" in such a case. The | |
291 | device will be considered "dead" in this case. | |
292 | ||
c9ab8b68 LV |
293 | Drivers for multi-function cards will need to coordinate among |
294 | themselves as to which driver instance will perform any "one-shot" | |
295 | or global device initialization. For example, the Symbios sym53cxx2 | |
296 | driver performs device init only from PCI function 0: | |
065c6359 | 297 | |
c9ab8b68 LV |
298 | + if (PCI_FUNC(pdev->devfn) == 0) |
299 | + sym_reset_scsi_bus(np, 0); | |
065c6359 | 300 | |
c9ab8b68 LV |
301 | Result codes: |
302 | - PCI_ERS_RESULT_DISCONNECT | |
303 | Same as above. | |
065c6359 | 304 | |
fe14acd4 | 305 | Drivers for PCI Express cards that require a fundamental reset must |
97e4e959 | 306 | set the needs_freset bit in the pci_dev structure in their probe function. |
fe14acd4 MM |
307 | For example, the QLogic qla2xxx driver sets the needs_freset bit for certain |
308 | PCI card types: | |
309 | ||
310 | + /* Set EEH reset type to fundamental if required by hba */ | |
311 | + if (IS_QLA24XX(ha) || IS_QLA25XX(ha) || IS_QLA81XX(ha)) | |
312 | + pdev->needs_freset = 1; | |
313 | + | |
314 | ||
c9ab8b68 LV |
315 | Platform proceeds either to STEP 5 (Resume Operations) or STEP 6 (Permanent |
316 | Failure). | |
317 | ||
fe14acd4 MM |
318 | >>> The current powerpc implementation does not try a power-cycle |
319 | >>> reset if the driver returned PCI_ERS_RESULT_DISCONNECT. | |
c9ab8b68 LV |
320 | >>> However, it probably should. |
321 | ||
322 | ||
323 | STEP 5: Resume Operations | |
324 | ------------------------- | |
325 | The platform will call the resume() callback on all affected device | |
326 | drivers if all drivers on the segment have returned | |
327 | PCI_ERS_RESULT_RECOVERED from one of the 3 previous callbacks. | |
328 | The goal of this callback is to tell the driver to restart activity, | |
329 | that everything is back and running. This callback does not return | |
330 | a result code. | |
331 | ||
332 | At this point, if a new error happens, the platform will restart | |
333 | a new error recovery sequence. | |
334 | ||
335 | STEP 6: Permanent Failure | |
336 | ------------------------- | |
337 | A "permanent failure" has occurred, and the platform cannot recover | |
338 | the device. The platform will call error_detected() with a | |
339 | pci_channel_state value of pci_channel_io_perm_failure. | |
340 | ||
341 | The device driver should, at this point, assume the worst. It should | |
342 | cancel all pending I/O, refuse all new I/O, returning -EIO to | |
343 | higher layers. The device driver should then clean up all of its | |
344 | memory and remove itself from kernel operations, much as it would | |
345 | during system shutdown. | |
346 | ||
347 | The platform will typically notify the system operator of the | |
348 | permanent failure in some way. If the device is hotplug-capable, | |
349 | the operator will probably want to remove and replace the device. | |
350 | Note, however, not all failures are truly "permanent". Some are | |
351 | caused by over-heating, some by a poorly seated card. Many | |
352 | PCI error events are caused by software bugs, e.g. DMA's to | |
353 | wild addresses or bogus split transactions due to programming | |
354 | errors. See the discussion in powerpc/eeh-pci-error-recovery.txt | |
355 | for additional detail on real-life experience of the causes of | |
356 | software errors. | |
357 | ||
358 | ||
359 | Conclusion; General Remarks | |
360 | --------------------------- | |
fe14acd4 | 361 | The way the callbacks are called is platform policy. A platform with |
c9ab8b68 | 362 | no slot reset capability may want to just "ignore" drivers that can't |
065c6359 LV |
363 | recover (disconnect them) and try to let other cards on the same segment |
364 | recover. Keep in mind that in most real life cases, though, there will | |
365 | be only one driver per segment. | |
366 | ||
c9ab8b68 | 367 | Now, a note about interrupts. If you get an interrupt and your |
065c6359 | 368 | device is dead or has been isolated, there is a problem :) |
c9ab8b68 LV |
369 | The current policy is to turn this into a platform policy. |
370 | That is, the recovery API only requires that: | |
065c6359 LV |
371 | |
372 | - There is no guarantee that interrupt delivery can proceed from any | |
373 | device on the segment starting from the error detection and until the | |
fe14acd4 MM |
374 | slot_reset callback is called, at which point interrupts are expected |
375 | to be fully operational. | |
065c6359 | 376 | |
c9ab8b68 LV |
377 | - There is no guarantee that interrupt delivery is stopped, that is, |
378 | a driver that gets an interrupt after detecting an error, or that detects | |
379 | an error within the interrupt handler such that it prevents proper | |
065c6359 | 380 | ack'ing of the interrupt (and thus removal of the source) should just |
c9ab8b68 LV |
381 | return IRQ_NOTHANDLED. It's up to the platform to deal with that |
382 | condition, typically by masking the IRQ source during the duration of | |
065c6359 LV |
383 | the error handling. It is expected that the platform "knows" which |
384 | interrupts are routed to error-management capable slots and can deal | |
c9ab8b68 | 385 | with temporarily disabling that IRQ number during error processing (this |
065c6359 LV |
386 | isn't terribly complex). That means some IRQ latency for other devices |
387 | sharing the interrupt, but there is simply no other way. High end | |
388 | platforms aren't supposed to share interrupts between many devices | |
389 | anyway :) | |
390 | ||
c9ab8b68 LV |
391 | >>> Implementation details for the powerpc platform are discussed in |
392 | >>> the file Documentation/powerpc/eeh-pci-error-recovery.txt | |
393 | ||
fe14acd4 MM |
394 | >>> As of this writing, there is a growing list of device drivers with |
395 | >>> patches implementing error recovery. Not all of these patches are in | |
c9ab8b68 LV |
396 | >>> mainline yet. These may be used as "examples": |
397 | >>> | |
fe14acd4 MM |
398 | >>> drivers/scsi/ipr |
399 | >>> drivers/scsi/sym53c8xx_2 | |
400 | >>> drivers/scsi/qla2xxx | |
401 | >>> drivers/scsi/lpfc | |
402 | >>> drivers/next/bnx2.c | |
c9ab8b68 LV |
403 | >>> drivers/next/e100.c |
404 | >>> drivers/net/e1000 | |
fe14acd4 | 405 | >>> drivers/net/e1000e |
c9ab8b68 | 406 | >>> drivers/net/ixgb |
fe14acd4 MM |
407 | >>> drivers/net/ixgbe |
408 | >>> drivers/net/cxgb3 | |
c9ab8b68 | 409 | >>> drivers/net/s2io.c |
fe14acd4 | 410 | >>> drivers/net/qlge |
c9ab8b68 LV |
411 | |
412 | The End | |
413 | ------- |