| Message ID | 20200303132852.13184-17-stanspas@amazon.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | Improve PCI device post-reset readiness polling | expand |
Hi Stanislav, Thanks for doing this! On Tue, Mar 03, 2020 at 02:28:51PM +0100, Stanislav Spassov wrote: > From: Stanislav Spassov <stanspas@amazon.de> > > The PCI Express specification dictates minimal amounts of time that the > host needs to wait after triggering different kinds of resets before it > is allowed to attempt accessing the device. After this waiting period, > devices are required to be responsive to Configuration Space reads. > However, if a device needs more time to actually complete the reset > operation internally, it may respond to the read with a Completion > Request Retry Status (CRS), and keep doing so on subsequent reads > for as long as necessary. If the device is broken, it may even keep > responding with CRS indefinitely. > > The specification also mandates that any Root Port that supports CRS > and has CRS Software Visibility (CRS SV) enabled will synthesize the > special value 0x0001 for the Vendor ID and set any other bits to 1 > upon receiving a CRS Completion for a Configuration Read Request that > includes both bytes of the Vendor ID (offset 0). > > IF CRS is supported by Root Port but CRS SV is not enabled, the request > is retried autonomously by the Root Port. Platform-specific configuration > registers may exist to limit the number of or time taken by such retries. Also when CRSV is enabled, config read that doesn't cover VENDOR is also retried automatically. > > If CRS is not supported, or a different register (not Vendor ID) is > polled, or the device is responding with CA/UR Completions (rather than > CRS), the behavior is platform-dependent, but generally the Root Port > synthesizes ~0 to complete the software read. > > Previously, pci_dev_wait() avoided taking advantage of CRS. However, > on platforms where no limit/timeout can be configured as explained > above, a device responding with CRS for too long (e.g. because it is > stuck and cannot complete its reset) may trigger more severe error > conditions (e.g. TOR timeout, 3-strike CPU CATERR), because the Root > Port never reports back to the lower-level component requesting the > transaction. > > This patch introduces special handling when CRS is available, and > otherwise falls back to the previous behavior of polling COMMAND. > > Signed-off-by: Stanislav Spassov <stanspas@amazon.de> > --- > drivers/pci/pci.c | 52 +++++++++++++++++++++++++++++++++++++++-------- > 1 file changed, 44 insertions(+), 8 deletions(-) > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c > index f1ba931b0ead..1a504419e0de 100644 > --- a/drivers/pci/pci.c > +++ b/drivers/pci/pci.c > @@ -1081,18 +1081,54 @@ static int pci_dev_wait(struct pci_dev *dev, enum pci_init_event event) > { > const char *event_name = pci_init_event_name(event); > int timeout = dev->reset_ready_poll_ms; > + int waited = 0; > + int rc = 0; > + > > /* > * After reset, the device should not silently discard config > * requests, but it may still indicate that it needs more time by > - * responding to them with CRS completions. The Root Port will > - * generally synthesize ~0 data to complete the read (except when > - * CRS SV is enabled and the read was for the Vendor ID; in that > - * case it synthesizes 0x0001 data). > - * > - * Wait for the device to return a non-CRS completion. Read the > - * Command register instead of Vendor ID so we don't have to > - * contend with the CRS SV value. > + * responding to them with CRS completions. For such completions: > + * - If CRS SV is enabled on the Root Port, and the read request > + * covers both bytes of the Vendor ID register, the Root Port > + * will synthesize the value 0x0001 (and set any extra requested > + * bytes to 0xff) > + * - If CRS SV is not enabled on the Root Port, the Root Port must > + * re-issue the Configuration Request as a new Request. > + * Depending on platform-specific Root Complex configurations, > + * the Root Port may stop retrying after a set number of attempts, > + * or a configured timeout is hit, or continue indefinitely > + * (ultimately resulting in non-PCI-specific platform errors, such as > + * a TOR timeout). > + */ > + if (dev->crssv_enabled) { > + u32 id; I like this check to read VENDOR_ID when crssv is enabled. But your patches seems to define in patch13 and used in patch16? can we keep them simple? and if possible just this would be a needed fix. We have some systems that we have found can cause timeouts if CRSV is enabled, but you read any other register other than the PCI_VENDOR. Would prefer to see this fix before the other cleanups can stabilize :-) I would also mark that for stable. > + > + rc = pci_dev_poll_until_not_equal(dev, PCI_VENDOR_ID, 0xffff, > + 0x0001, event_name, timeout, > + &waited, &id); > + if (rc) > + return rc; > + > + /* > + * If Vendor/Device ID is valid, the device must be ready. > + * Note: SR-IOV VFs return ~0 for reads to Vendor/Device > + * ID and will not be recognized as ready by this check. > + */ > + if (id != 0x0000ffff && id != 0xffff0000 && > + id != 0x00000000 && id != 0xffffffff) > + return 0; > + } > +
> > IF CRS is supported by Root Port but CRS SV is not enabled, the request > > is retried autonomously by the Root Port. Platform-specific configuration > > registers may exist to limit the number of or time taken by such retries. > > Also when CRSV is enabled, config read that doesn't cover VENDOR is > also retried automatically. > Agreed. This is explained in the very next sentence of the commit message, but I will see if I can re-order/re-phrase to make the explanation less confusing. > > > > + if (dev->crssv_enabled) { > > + u32 id; > > I like this check to read VENDOR_ID when crssv is enabled. But your patches > seems to define in patch13 and used in patch16? > > can we keep them simple? and if possible just this would be a > needed fix. We have some systems that we have found can cause > timeouts if CRSV is enabled, but you read any other register > other than the PCI_VENDOR. > > Would prefer to see this fix before the other cleanups can stabilize :-) > Makes sense. I guess I got ahead of myself when extending the original v1 of this patch series from only dealing with the CRS problem to "let's fix the world" :-) I will reorder my patches a bit and post them as two separate series, so that the CRS-related stuff can be pushed earlier and on its own while the rest stabilizes. > I would also mark that for stable. Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index f1ba931b0ead..1a504419e0de 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -1081,18 +1081,54 @@ static int pci_dev_wait(struct pci_dev *dev, enum pci_init_event event) { const char *event_name = pci_init_event_name(event); int timeout = dev->reset_ready_poll_ms; + int waited = 0; + int rc = 0; + /* * After reset, the device should not silently discard config * requests, but it may still indicate that it needs more time by - * responding to them with CRS completions. The Root Port will - * generally synthesize ~0 data to complete the read (except when - * CRS SV is enabled and the read was for the Vendor ID; in that - * case it synthesizes 0x0001 data). - * - * Wait for the device to return a non-CRS completion. Read the - * Command register instead of Vendor ID so we don't have to - * contend with the CRS SV value. + * responding to them with CRS completions. For such completions: + * - If CRS SV is enabled on the Root Port, and the read request + * covers both bytes of the Vendor ID register, the Root Port + * will synthesize the value 0x0001 (and set any extra requested + * bytes to 0xff) + * - If CRS SV is not enabled on the Root Port, the Root Port must + * re-issue the Configuration Request as a new Request. + * Depending on platform-specific Root Complex configurations, + * the Root Port may stop retrying after a set number of attempts, + * or a configured timeout is hit, or continue indefinitely + * (ultimately resulting in non-PCI-specific platform errors, such as + * a TOR timeout). + */ + if (dev->crssv_enabled) { + u32 id; + + rc = pci_dev_poll_until_not_equal(dev, PCI_VENDOR_ID, 0xffff, + 0x0001, event_name, timeout, + &waited, &id); + if (rc) + return rc; + + /* + * If Vendor/Device ID is valid, the device must be ready. + * Note: SR-IOV VFs return ~0 for reads to Vendor/Device + * ID and will not be recognized as ready by this check. + */ + if (id != 0x0000ffff && id != 0xffff0000 && + id != 0x00000000 && id != 0xffffffff) + return 0; + } + + /* + * Root Ports will generally indicate error scenarios (e.g. + * internal timeouts, or received Completion with CA/UR) by + * synthesizing an 'all bits set' value (~0). + * In case CRS is not supported/enabled, as well as for SR-IOV VFs, + * fall back to polling a different register that cannot validly + * contain ~0. As of PCIe 5.0, bits 11-15 of COMMAND are still RsvdP + * and must return 0 when read. + * XXX: These bits might become meaningful in the future */ return pci_dev_poll_until_not_equal(dev, PCI_COMMAND, ~0, ~0, event_name, timeout, NULL,