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.limoncie...@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
