Re: [PATCH v2] x86/video: Only fall back to vga_default_device() without screen info

[Thomas Zimmermann]

Hi

Am 23.06.26 um 16:15 schrieb Mario Limonciello:
> Some multi GPU systems may have a VGA compatible device, but that might
> not be used for display.  If due to enumeration order this device is
> found before the one actually used for display then multiple devices
> may show the boot_display attribute, confusing userspace.
>
> When screen info is valid, use it exclusively to find the primary
> device so that only the device backing the framebuffer is reported.
> Only when no framebuffer has been set up does it make sense to fall
> back to the default VGA device.  This ensures at most one primary
> graphics device, preferably the one with the framebuffer.
>
> Suggested-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Fixes: ad90860bd10ee ("fbcon: Use screen info to find primary device")
> Reported-by: Aaron Ma <aaron.ma@xxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-pci/20260618081803.2790848-1-aaron.ma@xxxxxxxxxxxxx/#t
> Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>

Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx>

This looks good. Thanks for fixing this issue.

Best regards
Thomas

> ---
> v1->v2:
>    * Fix subject
>    * Keep vga_default_device() as fallback instead of remove all
>      together
>   arch/x86/video/video-common.c | 23 ++++++++++++++---------
>   1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c
> index 152789f00fcda..8ed82fff7638e 100644
> --- a/arch/x86/video/video-common.c
> +++ b/arch/x86/video/video-common.c
> @@ -43,21 +43,26 @@ 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) {
> -		if (!(res[i].flags & IORESOURCE_MEM))
> -			continue;
> +	if (numres > 0) {
> +		for (i = 0; i < numres; ++i) {
> +			if (!(res[i].flags & IORESOURCE_MEM))
> +				continue;
> +
> +			if (pci_find_resource(pdev, &res[i]))
> +				return true;
> +		}
>   
> -		if (pci_find_resource(pdev, &res[i]))
> -			return true;
> +		return false;
>   	}
>   #endif
>   
> -	return false;
> +	/*
> +	 * No framebuffer was set up by the firmware/bootloader, so fall back
> +	 * to the default VGA device.
> +	 */
> +	return pdev == vga_default_device();
>   }
>   EXPORT_SYMBOL(video_is_primary_device);
>   

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)