[PATCH v9 0/9] Adjust fbcon console device detection

[Mario Limonciello]

On 7/24/2025 1:36 PM, Bjorn Helgaas wrote:
> On Thu, Jul 17, 2025 at 03:56:58PM -0500, Bjorn Helgaas wrote:
>> On Thu, Jul 17, 2025 at 12:38:03PM -0500, Mario Limonciello wrote:
>>> From: Mario Limonciello <mario.limonciello at amd.com>
>>>
>>> Systems with more than one GPU userspace doesn't know which one to be
>>> used to treat as primary.  The concept of primary is important to be
>>> able to decide which GPU is used for display and  which is used for
>>> rendering.  If it's guessed wrong then both GPUs will be kept awake
>>> burning a lot of power.
>>>
>>> Historically it would use the "boot_vga" attribute but this isn't
>>> present on modern GPUs.
>>>
>>> This series started out as changes to VGA arbiter to try to handle a case
>>> of a system with 2 GPUs that are not VGA devices and avoid changes to
>>> userspace.  This was discussed but decided not to overload the VGA arbiter
>>> for non VGA devices.
>>>
>>> Instead move the x86 specific detection of framebuffer resources into x86
>>> specific code that the fbcon can use to properly identify the primary
>>> device. This code is still called from the VGA arbiter, and the logic does
>>> not change there. To avoid regression default to VGA arbiter and only fall
>>> back to looking up with x86 specific detection method.
>>>
>>> In order for userspace to also be able to discover which device was the
>>> primary video display device create a new sysfs file 'boot_display'.
>>>
>>> A matching userspace implementation for this file is available here:
>>> Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/39
>>> Link: https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2038
>>>
>>> Dave Airlie has been pinged for a comment on this approach.
>>> Dave had suggested in the past [1]:
>>>
>>> "
>>>   But yes if that doesn't work, then maybe we need to make the boot_vga
>>>   flag mean boot_display_gpu, and fix it in the kernel
>>> "
>>>
>>> This was one of the approached tried in earlier revisions and it was
>>> rejected in favor of creating a new sysfs file (which is what this
>>> version does).
>>>
>>> It is suggested that this series merge entirely through the PCI tree.
>>>
>>> Link: https://gitlab.freedesktop.org/xorg/lib/libpciaccess/-/merge_requests/37#note_2938602 [1]
>>>
>>> v9:
>>>   * Add more to cover letter
>>>   * Add bug link to last patch
>>>   * Update commit message for last patch
>>>   * Update boot_display documentation description
>>>
>>> Mario Limonciello (9):
>>>    PCI: Add helper for checking if a PCI device is a display controller
>>>    vfio/pci: Use pci_is_display()
>>>    vga_switcheroo: Use pci_is_display()
>>>    iommu/vt-d: Use pci_is_display()
>>>    ALSA: hda: Use pci_is_display()
>>>    Fix access to video_is_primary_device() when compiled without
>>>      CONFIG_VIDEO
>>>    PCI/VGA: Replace vga_is_firmware_default() with a screen info check
>>>    fbcon: Use screen info to find primary device
>>>    PCI: Add a new 'boot_display' attribute
>>>
>>>   Documentation/ABI/testing/sysfs-bus-pci |  9 +++++
>>>   arch/parisc/include/asm/video.h         |  2 +-
>>>   arch/sparc/include/asm/video.h          |  2 ++
>>>   arch/x86/include/asm/video.h            |  2 ++
>>>   arch/x86/video/video-common.c           | 17 ++++++++-
>>>   drivers/gpu/vga/vga_switcheroo.c        |  2 +-
>>>   drivers/iommu/intel/iommu.c             |  2 +-
>>>   drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>>>   drivers/pci/vgaarb.c                    | 31 +++--------------
>>>   drivers/vfio/pci/vfio_pci_igd.c         |  3 +-
>>>   include/linux/pci.h                     | 15 ++++++++
>>>   sound/hda/hdac_i915.c                   |  2 +-
>>>   sound/pci/hda/hda_intel.c               |  4 +--
>>>   13 files changed, 102 insertions(+), 35 deletions(-)
>>
>> Applied to pci/boot-display for v6.17, thanks!
> 
> I kept the pci_is_display() changes but deferred the following for now:
> 
>    Fix access to video_is_primary_device() when compiled without CONFIG_VIDEO
>    PCI/VGA: Replace vga_is_firmware_default() with a screen info check
>    fbcon: Use screen info to find primary device
>    PCI: Add a new 'boot_display' attribute
> 
> I think the boot_display attribute isn't quite baked yet and I don't
> want to add something when it looks like we're immediately going to
> change the implementation and maybe the sysfs location.
> 
> Bjorn

Thanks for the update.

The patch moving to DRM does have an Acked-by.

At this point do you think there is still a shot at a squashed/rebased 
version of those for 6.17, or should I rebase and submit the outcome for 
discussion targeting 6.18 after the merge window?