On Tue, Oct 15, 2019 at 7:31 AM Daniel Drake <drake@xxxxxxxxxxxx> wrote: > > On Mon, Oct 14, 2019 at 11:43 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > Can you tell if this is because the Ryzen7 XHCI controller is out of > > spec, or is the Linux PCI core missing some delay? If the latter, > > fixing the core might fix other devices as well. > > > > Mika has this patch: > > https://lore.kernel.org/r/20190821124519.71594-1-mika.westerberg@xxxxxxxxxxxxxxx > > for similar issues, but I think that patch fixes D3cold->D0 > > transitions, and your patch appears to be concerned with D3hot->D0 > > transitions. > > It's actually coming out of D3cold here, however what happens right > before this is that __pci_start_power_transition() calls > pci_platform_power_transition(D0) to leave D3cold state, then > pci_update_current_state() reads PMCSR and updates dev->current_state > to D3hot. Which pci_update_current_state() do you mean, exactly? Note that pci_platform_power_transition() itself contains one, which triggers after a successful change of the ACPI power state of the device (which should be the case here). Then, there is one in pci_power_up(), but before that the device's PMCSR is read from and written to in pci_raw_set_power_state(). It looks like the reads from it after the ACPI power state change are all successful, but the write isn't unless there is the delay between it and the former platform_pci_set_power_state(). > The 20ms delay for these XHCI controllers is needed precisely at this > point - after writing PMCSR to move to D0, and before reading it back > to check the result. > I tried moving the delay immediately before writing PMCSR, but that > doesn't work. Based on that, it seems like it's just a little out of > spec. That I agree with and the platform firmware doesn't compensate for that (which it could do, arguably).
