Re: [PATCH] PCI: Add quirk to clear MSI-X

[Bjorn Helgaas <helgaas@kernel.org>]

Let's mention the vendor and device name in the subject to make the
log more useful.

On Mon, Mar 06, 2023 at 12:53:40PM +0530, Basavaraj Natikar wrote:
> One of the AMD USB controllers fails to maintain internal functional
> context when transitioning from D3 to D0, desynchronizing MSI-X bits.
> As a result, add a quirk to this controller to clear the MSI-X bits
> on suspend.

Is this a documented erratum?  Please include a citation if so.

Are there any other AMD USB devices with the same defect?

The quick clears the Function Mask bit, so the MSI-X vectors may be
*unmasked* depending on the state of each vectors Mask bit.  I assume
the potential unmasking is safe because you also clear the MSI-X
Enable bit, so the function can't use MSI-X at all.

All state is lost in D3cold, so I guess this problem must occur during
a D3hot to D0 transition, right?  I assume this device sets
No_Soft_Reset, so the function is supposed to return to D0active with
all internal state intact.  But this device returns to D0active with
the MSI-X internal state corrupted?

I assume this relies on pci_restore_state() to restore the MSI-X
state.  Seems like that might be enough to restore the internal state
even without this quirk, but I guess it must not be.

> Note: This quirk works in all scenarios, regardless of whether the
> integrated GPU is disabled in the BIOS.

I don't know how the integrated GPU is related to this USB controller,
but I assume this fact is important somehow?

> Cc: Mario Limonciello <mario.limonciello@amd.com>
> Reported-by: Thomas Glanzmann <thomas@glanzmann.de>
> Link: https://lore.kernel.org/linux-usb/Y%2Fz9GdHjPyF2rNG3@glanzmann.de/T/#u

Apparently the symptom is one of these:

  xhci_hcd 0000:0c:00.0: Error while assigning device slot ID: Command Aborted
  xhci_hcd 0000:0c:00.0: Max number of devices this xHCI host supports is 64.
  usb usb1-port1: couldn't allocate usb_device
  xhci_hcd 0000:0c:00.0: WARN: xHC save state timeout
  xhci_hcd 0000:0c:00.0: PM: suspend_common(): xhci_pci_suspend+0x0/0x150 [xhci_pci] returns -110
  xhci_hcd 0000:0c:00.0: can't suspend (hcd_pci_runtime_suspend [usbcore] returned -110)

We should include the critical line or two in the commit log to help
users find the fix.

I see this must be xhci_suspend() returning -ETIMEDOUT after
xhci_save_registers(), but I don't see the connection from there to a
PCI_FIXUP_SUSPEND.  Can you connect the dots for me?

> Signed-off-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
> ---
>  drivers/pci/quirks.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 44cab813bf95..ddf7100227d3 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -6023,3 +6023,13 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x9a2d, dpc_log_size);
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x9a2f, dpc_log_size);
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x9a31, dpc_log_size);
>  #endif
> +
> +static void quirk_clear_msix(struct pci_dev *dev)
> +{
> +	u16 ctrl;
> +
> +	pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &ctrl);
> +	ctrl &= ~(PCI_MSIX_FLAGS_MASKALL | PCI_MSIX_FLAGS_ENABLE);
> +	pci_write_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, ctrl);
> +}
> +DECLARE_PCI_FIXUP_SUSPEND(PCI_VENDOR_ID_AMD, 0x15b8, quirk_clear_msix);
> -- 
> 2.25.1
>