Re: [PATCH] PCI: vgaarb: Include 0x0380 devices in default selection

[Aaron Ma]

On Mon, Jun 22, 2026 at 12:00 PM Mario Limonciello
<mario.limonciello@xxxxxxx> wrote:
>
>
>
> On 6/21/26 20:50, Aaron Ma wrote:
> > On Mon, Jun 22, 2026 at 1:15 AM Mario Limonciello
> > <mario.limonciello@xxxxxxx> wrote:
> >>
> >>
> >>
> >> On 6/18/26 01:18, Aaron Ma wrote:
> >>> Some firmware boot GPUs report class 0x0380 (PCI_CLASS_DISPLAY_OTHER)
> >>> instead of PCI_CLASS_DISPLAY_VGA. vgaarb only registers pci_is_vga()
> >>> devices, so those GPUs are not considered by vga_is_firmware_default().
> >>>
> >>> On these systems the AMD GPU matches the EFI framebuffer but is
> >>> excluded from vgaarb because it is class 0x0380, while the NVIDIA GPU
> >>> does not match the EFI framebuffer but becomes vga_default_device()
> >>> through the vgaarb's enabled-device fallback.
> >>>
> >>> Register legacy VGA and 0x0380 devices in vgaarb, and expose boot_vga
> >>> for the same set of devices, so the firmware default device can be
> >>> selected correctly.
> >>>
> >>> Signed-off-by: Aaron Ma <aaron.ma@xxxxxxxxxxxxx>
> >>> ---
> >>>    drivers/pci/pci-sysfs.c |  3 ++-
> >>>    drivers/pci/vgaarb.c    | 10 +++++-----
> >>>    include/linux/pci.h     | 14 ++++++++++++++
> >>>    3 files changed, 21 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> >>> index d37860841260c..843d83ec9550a 100644
> >>> --- a/drivers/pci/pci-sysfs.c
> >>> +++ b/drivers/pci/pci-sysfs.c
> >>> @@ -1717,7 +1717,8 @@ static umode_t pci_dev_attrs_are_visible(struct kobject *kobj,
> >>>        struct device *dev = kobj_to_dev(kobj);
> >>>        struct pci_dev *pdev = to_pci_dev(dev);
> >>>
> >>> -     if (a == &dev_attr_boot_vga.attr && pci_is_vga(pdev))
> >>> +     if (a == &dev_attr_boot_vga.attr &&
> >>> +         pci_is_vga_or_other_display(pdev))
> >>>                return a->mode;
> >>   >   >          if (a == &dev_attr_serial_number.attr && pci_get_dsn(pdev))
> >>> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> >>> index c360eee11dd9e..0e0878189e3d8 100644
> >>> --- a/drivers/pci/vgaarb.c
> >>> +++ b/drivers/pci/vgaarb.c
> >>> @@ -796,7 +796,7 @@ static bool vga_arbiter_add_pci_device(struct pci_dev *pdev)
> >>>        }
> >>>
> >>>        if (vga_is_boot_device(vgadev)) {
> >>> -             vgaarb_info(&pdev->dev, "setting as boot VGA device%s\n",
> >>> +             vgaarb_info(&pdev->dev, "setting as boot display device%s\n",
> >>>                            vga_default_device() ?
> >>>                            " (overriding previous)" : "");
> >>>                vga_set_default_device(pdev);
> >>> @@ -1483,8 +1483,8 @@ static int pci_notify(struct notifier_block *nb, unsigned long action,
> >>>
> >>>        vgaarb_dbg(dev, "%s\n", __func__);
> >>>
> >>> -     /* Only deal with VGA class devices */
> >>> -     if (!pci_is_vga(pdev))
> >>> +     /* Only deal with legacy VGA and other display controller devices */
> >>> +     if (!pci_is_vga_or_other_display(pdev)) >               return 0;
> >>>
> >>>        /*
> >>> @@ -1530,12 +1530,12 @@ static int __init vga_arb_device_init(void)
> >>>
> >>>        bus_register_notifier(&pci_bus_type, &pci_notifier);
> >>>
> >>> -     /* Add all VGA class PCI devices by default */
> >>> +     /* Add legacy VGA and other display controller PCI devices by default */
> >>>        pdev = NULL;
> >>>        while ((pdev =
> >>>                pci_get_subsys(PCI_ANY_ID, PCI_ANY_ID, PCI_ANY_ID,
> >>>                               PCI_ANY_ID, pdev)) != NULL) {
> >>> -             if (pci_is_vga(pdev))
> >>> +             if (pci_is_vga_or_other_display(pdev))
> >>>                        vga_arbiter_add_pci_device(pdev);
> >>>        }
> >>>
> >>> diff --git a/include/linux/pci.h b/include/linux/pci.h
> >>> index 2c4454583c115..195ec1bdac863 100644
> >>> --- a/include/linux/pci.h
> >>> +++ b/include/linux/pci.h
> >>> @@ -792,6 +792,20 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
> >>>        return false;
> >>>    }
> >>>
> >>> +/**
> >>> + * pci_is_vga_or_other_display - check if the PCI device is VGA or 0x0380
> >>> + * @pdev: PCI device
> >>> + *
> >>> + * Return true for legacy VGA-compatible devices and for "other display
> >>> + * controller" devices.  Some firmware-selected boot display devices expose
> >>> + * class 0x0380 instead of PCI_CLASS_DISPLAY_VGA.
> >>> + */
> >>> +static inline bool pci_is_vga_or_other_display(struct pci_dev *pdev)
> >>> +{
> >>> +     return pci_is_vga(pdev) ||
> >>> +             (pdev->class >> 8) == PCI_CLASS_DISPLAY_OTHER;
> >>> +}
> >>> +
> >>>    /**
> >>>     * pci_is_display - check if the PCI device is a display controller
> >>>     * @pdev: PCI device
> >>
> >>
> >> This patch doesn't seem correct to me.  It's overloading the purpose of
> >> boot_vga to cover non VGA devices.  We should be using boot_display.
> >>
> >> Trying to hypothesize what's going on here - I guess you're seeing
> >> boot_display set for more than one device due to enumeration order.
> >>
> >> Can you see if this helps instead?
> >>
> >> ╰─❯ git diff
> >> diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c
> >> index 152789f00fcda..9440eb3a7b15d 100644
> >> --- a/arch/x86/video/video-common.c
> >> +++ b/arch/x86/video/video-common.c
> >> @@ -43,9 +43,6 @@ bool video_is_primary_device(struct device *dev)
> >>           if (!pci_is_display(pdev))
> >>                   return false;
> >>
> >> -       if (pdev == vga_default_device())
> >> -               return true;
> >> -
> >>    #ifdef CONFIG_SCREEN_INFO
> >>           numres = screen_info_resources(si, res, ARRAY_SIZE(res));
> >>           for (i = 0; i < numres; ++i) {
> >
> > Hi Mario,
> >
> > I tested your change. boot_display becomes correct, but the issue is not fixed.
> >
> > The kernel state becomes:
> >
> >    AMD:    boot_display=1, boot_vga absent
> >    NVIDIA: boot_display absent, boot_vga=1
> >
> > Current Xorg checks boot_display || boot_vga, so both GPUs still match.
> > The selected primary GPU still depends on Xorg's DRM device enumeration order.
> >
> > So boot_vga is still wrong, and that still matters. The kernel should not
> > expose boot_vga=1 for NVIDIA when the firmware framebuffer is on AMD.
> >
> > My patch makes boot_vga and boot_display agree on the AMD boot display.
> >
> > Thanks,
> > Aaron
>
> Got it.  I still don't think it's correct to overload boot_vga.  It
> would be better for us to not show boot_vga at all - because it's not
> correct.
>
> Maybe we should drop the fallback code in VGA arbiter that is setting
> NVIDIA as boot_vga at all.
>
> Could you look at doing that?
>

Hi Mario,

I looked at dropping the fallback. I don't think we should remove it globally;
old systems may still need vga_default_device() when no firmware framebuffer
owner can be identified.

For v2 I will keep the fallback, but avoid the wrong result on this system. The
0x0380 firmware display can become the default/boot_vga device, while legacy
VGA decoding and ownership stay limited to pci_is_vga() devices.

So this keeps compatibility, but avoids reporting NVIDIA as boot_vga when the
firmware framebuffer is on AMD.

Thanks,
Aaron