On Thursday, April 19, 2018 11:05:19 PM CEST Bjorn Helgaas wrote: > The ASPM L1.2 substate depends on LTR information. Per the PCI > Firmware spec, the OS is supposed to negotiate with the platform for > control of the LTR feature, but previously we didn't do that. > > In addition, we must not enable LTR in an endpoint unless the Root > Complex and all intermediate switches also support LTR. We already > took care of that in pci_configure_ltr(), but we didn't ensure that > LTR was enabled before allowing ASPM L1.2 to be enabled. > > These patches fix both of these issues. Or rather, they *should* fix > them. I don't have hardware to test them, so any help with testing > would be appreciated. > > I think the most likely issue would be a platform where the hardware > supports LTR and the ASPM L1.2 substate, but the BIOS doesn't support > LTR in _OSC. In that case, we previously could have enabled ASPM L1.2 > (though it probably wouldn't work correctly), and after these patches, > we should not enable ASPM L1.2. > > You can look for issues by comparing dmesg and "lspci -vv" output > before and after these patches. > > It would also be interesting to collect an acpidump from platforms > that support LTR, even if there's no endpoint that supports ASPM L1.2. > The acpidump should show that _OSC supports LTR. > > I included some NVMe folks because these were motivated by Srinath's > recent report of LTR and ASPM issues with a Samsung NVMe SSD > Controller SM961/PM961 device, so this is sort of FYI in case you see > similar issues or are in a position to test these. > > --- > > Bjorn Helgaas (2): > PCI/ASPM: Disable ASPM L1.2 Substate if we don't have LTR > PCI/ACPI: Request LTR control from platform before using it For both: Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
