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

[Alex Deucher]

On Mon, Mar 18, 2024 at 3:52 PM Alex Deucher <alexdeucher at gmail.com> wrote:
>
> 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.

Is there a reason why you need this option?  Even beyond this, I could
envision other problems related to APUs and ACPI if these changed.

Alex