Re: [PATCH] pci: Avoid FLR for AMD FCH AHCI adapters

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Mario, Shyam, Brijesh]

On Sat, Jan 28, 2023 at 10:39:51AM +0900, Damien Le Moal wrote:
> PCI passthrough to VMs does not work with AMD FCH AHCI adapters: the
> guest OS fails to correctly probe devices attached to the controller due
> to FIS communication failures. 

What does a FIS communication failure look like?  Can we include a
line or two of dmesg output here to help users find this fix?

AMD folks: Can you confirm/deny that this is a hardware erratum in
this device?  Do you know of any other devices that need a similar
workaround?

> Forcing the "bus" reset method before
> unbinding & binding the adapter to the vfio-pci driver solves this
> issue. I.e.:
> 
> echo "bus" > /sys/bus/pci/devices/<ID>/reset_method
> 
> gives a working guest OS, thus indicating that the default flr reset
> method is defective, resulting in the adapter not being reset correctly.
> 
> This patch applies the no_flr quirk to AMD FCH AHCI devices to
> permanently solve this issue.
> 
> Reported-by: Niklas Cassel <niklas.cassel@wdc.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> ---
>  drivers/pci/quirks.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 285acc4aaccc..20ac67d59034 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -5340,6 +5340,7 @@ static void quirk_no_flr(struct pci_dev *dev)
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_AMD, 0x1487, quirk_no_flr);
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_AMD, 0x148c, quirk_no_flr);
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_AMD, 0x149c, quirk_no_flr);
> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_AMD, 0x7901, quirk_no_flr);
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1502, quirk_no_flr);
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x1503, quirk_no_flr);
>  
> -- 
> 2.39.1
>