On Mon, Oct 14, 2019 at 11:43 PM Bjorn Helgaas <helg...@kernel.org> 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.westerb...@linux.intel.com > 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. 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. With Mika's patch, pcie_wait_downstream_accessible() is called for these devices after the state transition has already failed. It also doesn't do any delaying at that point because pci_pcie_type(pdev) == 0. Daniel