linux-kernel - Re: [PATCH] PCI/VGA: Don't assume only VGA device found is the boot VGA device

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Message-ID: <CADnq5_OjfJzcOqa=NbWVw5ENvi+nmvNAZX0u_0hOvk3EVoh0bw@mail.gmail.com>
Date: Tue, 22 Oct 2024 09:04:30 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Kai-Heng Feng <kaihengf@...dia.com>
Cc: Luke Jones <luke@...nes.dev>, Mario Limonciello <superm1@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>, 
	open list <linux-kernel@...r.kernel.org>, dri-devel@...ts.freedesktop.org, 
	Mario Limonciello <mario.limonciello@....com>, Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH] PCI/VGA: Don't assume only VGA device found is the boot
 VGA device

On Tue, Oct 22, 2024 at 2:31 AM Kai-Heng Feng <kaihengf@...dia.com> wrote:
>
> Hi Luke,
>
> On 2024/10/15 4:04 PM, Luke Jones wrote:
> > On Mon, 14 Oct 2024, at 5:25 PM, Mario Limonciello wrote:
> >> From: Mario Limonciello <mario.limonciello@....com>
> >>
> >> The ASUS GA605W has a NVIDIA PCI VGA device and an AMD PCI display device.
> >>
> >> ```
> >> 65:00.0 VGA compatible controller: NVIDIA Corporation AD106M [GeForce
> >> RTX 4070 Max-Q / Mobile] (rev a1)
> >> 66:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI]
> >> Strix [Radeon 880M / 890M] (rev c1)
> >> ```
> >>
> >> The fallback logic in vga_is_boot_device() flags the NVIDIA dGPU as the
> >> boot VGA device, but really the eDP is connected to the AMD PCI display
> >> device.
> >>
> >> Drop this case to avoid marking the NVIDIA dGPU as the boot VGA device.
> >>
> >> Suggested-by: Alex Deucher <alexander.deucher@....com>
> >> Reported-by: Luke D. Jones <luke@...nes.dev>
> >> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3673
> >> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> >> ---
> >>   drivers/pci/vgaarb.c | 7 -------
> >>   1 file changed, 7 deletions(-)
> >>
> >> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> >> index 78748e8d2dba..05ac2b672d4b 100644
> >> --- a/drivers/pci/vgaarb.c
> >> +++ b/drivers/pci/vgaarb.c
> >> @@ -675,13 +675,6 @@ static bool vga_is_boot_device(struct vga_device *vgadev)
> >>              return true;
> >>      }
> >>
> >> -    /*
> >> -     * Vgadev has neither IO nor MEM enabled.  If we haven't found any
> >> -     * other VGA devices, it is the best candidate so far.
> >> -     */
> >> -    if (!boot_vga)
> >> -            return true;
> >> -
> >>      return false;
> >>   }
> >>
> >> --
> >> 2.43.0
> >
> > Hi Mario,
> >
> > I can verify that this does leave the `boot_vga` attribute set as 0 for the NVIDIA device.
>
> Does the following diff work for you?
> This variant should be less risky for most systems.
>
> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> index 78748e8d2dba..3fb734cb9c1b 100644
> --- a/drivers/pci/vgaarb.c
> +++ b/drivers/pci/vgaarb.c
> @@ -675,6 +675,9 @@ static bool vga_is_boot_device(struct vga_device *vgadev)
>                  return true;
>          }
>
> +       if (vga_arb_integrated_gpu(&pdev->dev))
> +               return true;
> +

The problem is that the integrated graphics does not support VGA.

Alex

>          /*
>           * Vgadev has neither IO nor MEM enabled.  If we haven't found any
>           * other VGA devices, it is the best candidate so far.
>
>
> Kai-Heng
>
> >
> > Tested-by: Luke D. Jones <luke@...nes.dev>
>