Re: [PATCH] x86/video: Preserve the default VGA fallback for legacy modes

[sashiko-bot@kernel.org]

> Commit 596b3678326d ("x86/video: Only fall back to vga_default_device()
> without screen info") made video_is_primary_device() rely exclusively
> on screen_info resources whenever any are available.
> 
> However, screen_info_resources() also returns legacy I/O and memory
> ranges for VGA text modes. These ranges are not PCI BARs, so the resource
> lookup fails and the default VGA fallback is skipped.
> 
> On a SeaBIOS QEMU guest with bochs and VKMS, the boot VGA loses its DRM
> boot_display attribute and fbcon leaves the console on VKMS. This can
> be checked with:
> 
>     cat /sys/class/drm/card1/boot_display
>     stty -F /dev/tty1 size
> 
> Without the fix, boot_display is missing and tty1 is 48 rows by 128
> columns. With it, boot_display contains 1 and tty1 is 50 rows by 160
> columns.
> 
> Use resource-based selection only for linear framebuffers. Fall back to
> vga_default_device() for legacy display modes, while keeping EFI and
> VESA framebuffer ownership authoritative.
> 
> Fixes: 596b3678326d ("x86/video: Only fall back to vga_default_device() without screen info")
> Cc: stable@vger.kernel.org
> Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261029162311.3389523-1-hengyul@cs.unc.edu?part=1