Re: [PATCH v3] PCI/VGA: Select SCREEN_INFO on X86

[Thomas Zimmermann <tzimmermann@suse.de>]

Am 14.10.25 um 00:08 schrieb Mario Limonciello (AMD):
> commit 337bf13aa9dda ("PCI/VGA: Replace vga_is_firmware_default() with
> a screen info check") introduced an implicit dependency upon SCREEN_INFO
> by removing the open coded implementation.
>
> If a user didn't have CONFIG_SCREEN_INFO set vga_is_firmware_default()
> would now return false.  SCREEN_INFO is only used on X86 so add add a
> conditional select for SCREEN_INFO to ensure that the VGA arbiter works
> as intended.
>
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Closes: https://lore.kernel.org/linux-pci/20251012182302.GA3412@sol/
> Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
> Fixes: 337bf13aa9dda ("PCI/VGA: Replace vga_is_firmware_default() with a screen info check")
> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
>   drivers/pci/Kconfig  | 1 +
>   drivers/pci/vgaarb.c | 6 ++----
>   2 files changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 7065a8e5f9b14..f94f5d384362e 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -306,6 +306,7 @@ config VGA_ARB
>   	bool "VGA Arbitration" if EXPERT
>   	default y
>   	depends on (PCI && !S390)
> +	select SCREEN_INFO if X86

On x86 screen_info comes from [1]. On other systems it's at [2].

You can try selecting CONFIG_SYSFB instead, but that will likely run 
into trouble with CONFIG_EFI=n.

[1] 
https://elixir.bootlin.com/linux/v6.17.1/source/arch/x86/kernel/setup.c#L214
[2] 
https://elixir.bootlin.com/linux/v6.17.1/source/drivers/firmware/efi/efi-init.c#L63

I guess, the current patch should work for the use case. I'll keep in 
mind to make the screen_info state easier to select.

Best regards
Thomas

>   	help
>   	  Some "legacy" VGA devices implemented on PCI typically have the same
>   	  hard-decoded addresses as they did on ISA. When multiple PCI devices
> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> index b58f94ee48916..436fa7f4c3873 100644
> --- a/drivers/pci/vgaarb.c
> +++ b/drivers/pci/vgaarb.c
> @@ -556,10 +556,8 @@ EXPORT_SYMBOL(vga_put);
>   
>   static bool vga_is_firmware_default(struct pci_dev *pdev)
>   {
> -#ifdef CONFIG_SCREEN_INFO
> -	struct screen_info *si = &screen_info;
> -
> -	return pdev == screen_info_pci_dev(si);
> +#if defined CONFIG_X86
> +	return pdev == screen_info_pci_dev(&screen_info);
>   #else
>   	return false;
>   #endif

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)