[PATCH] drm/amdgpu: Remove pci address checks from acpi_vfct_bios

[Alex Deucher]

On Mon, Mar 18, 2024 at 12:06 PM Kurt Kartaltepe <kkartaltepe at gmail.com> wrote:
>
> On Mon, Mar 18, 2024 at 8:42 AM Alex Deucher <alexdeucher at gmail.com> wrote:
> >
> > On Mon, Mar 18, 2024 at 10:19 AM Kurt Kartaltepe <kkartaltepe at gmail.com> wrote:
> > >
> > > On Mon, Mar 18, 2024 at 6:37 AM Alex Deucher <alexdeucher at gmail.com> wrote:
> > > >
> > > > On Mon, Mar 18, 2024 at 4:47 AM Kurt Kartaltepe <kkartaltepe at gmail.com> wrote:
> > > > >
> > > > > These checks prevent using amdgpu with the pcie=assign-busses parameter
> > > > > which will re-address devices from their acpi values.
> > > > >
> > > > > Signed-off-by: Kurt Kartaltepe <kkartaltepe at gmail.com>
> > > >
> > > > This will likely break multi-GPU functionality.  The BDF values are
> > > > how the sbios/driver differentiates between the VFCT images.  If you
> > > > have multiple GPUs in the system, the driver won't be able to figure
> > > > out which one goes with which GPU an you may end up assigning the
> > > > wrong image to the wrong device.
> > > >
> > > > Alex
> > >
> > > The vendor and device portions must be correct in the existing
> > > kernels, so device type differentiation should already work without
> > > BDF values.
> > >
> > > So does that mean the concern is images are different for devices with
> > > the same vendor:device pairs? There are sites out there dedicated to
> > > dumping AMD's video roms which seem to suggest all discrete devices
> > > would be fine loading the same rom. Is there another platform you are
> > > thinking of where devices with the same vendor:device values would
> > > need different images?
> >
> > That is incorrect.  The vbios images are board specific.  Using the
> > wrong image can cause a lot of problems.  The vbios exists to handle
> > board specific design variations (e.g., the number and type of display
> > connectors, the i2c/aux channel mappings, board specific clock and
> > voltage settings, etc.).  The PCI DID just indicates the chip used on
> > the board.  The actual board design varies with each AIB vendor (e.g.,
> > Sapphire and XFX both make 7900XTX boards, but they can have very
> > different configurations.
>
> Thanks for the explanation, that makes sense.
>
> Is my understanding correct that IGPUs (my case) simply won't have
> vbios available in any other mechanism. If so perhaps this isnt
> feasible in amdgpu as the BDF information is lost in reassignment.

Depends on the platform, but recent ones use VFCT.  That said, there
should only ever be one IGPU in the system so I think we could just
rely on the VID and DID for APUs in this case and check everything for
dGPUs.

Alex