Re: [PATCH v3 3/3] x86/quirks: Fix stolen detection with integrated + discrete GPU

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Jan 07, 2022 at 01:05:16PM -0800, Lucas De Marchi wrote:
> early_pci_scan_bus() does a depth-first traversal, possibly calling
> the quirk functions for each device based on vendor, device and class
> from early_qrk table. intel_graphics_quirks() however uses PCI_ANY_ID
> and does additional filtering in the quirk.
> 
> If there is an Intel integrated + discrete GPU the quirk may be called
> first for the discrete GPU based on the PCI topology. Then we will fail
> to reserve the system stolen memory for the integrated GPU, because we
> will already have marked the quirk as "applied".
> 
> This was reproduced in a setup with Alderlake-P (integrated) + DG2
> (discrete), with the following PCI topology:
> 
> 	- 00:01.0 Bridge
> 	  `- 03:00.0 DG2
> 	- 00:02.0 Integrated GPU
> 
> Move the setting of quirk_applied in intel_graphics_quirks() so it's
> mark as applied only when we find the integrated GPU based on the
> intel_early_ids table.
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

I don't know the details of stolen memory, but the implementation of
this quirk looks good to me.  Very nice that it's now very clear
exactly what the change is.

> ---
> 
> v3: now that we do the refactor before the fix, we can do a single line
> change to fix intel_graphics_quirks(). Also, we don't change
> intel_graphics_stolen() anymore as we did in v2: we don't have to check
> other devices anymore if there was a previous match causing
> intel_graphics_stolen() to be called (there can only be one integrated
> GPU reserving the stolen memory).
> 
>  arch/x86/kernel/early-quirks.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index df34963e23bf..932f9087c324 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -609,8 +609,6 @@ static void __init intel_graphics_quirks(int num, int slot, int func)
>  	if (quirk_applied)
>  		return;
>  
> -	quirk_applied = true;
> -
>  	device = read_pci_config_16(num, slot, func, PCI_DEVICE_ID);
>  
>  	for (i = 0; i < ARRAY_SIZE(intel_early_ids); i++) {
> @@ -623,6 +621,8 @@ static void __init intel_graphics_quirks(int num, int slot, int func)
>  
>  		intel_graphics_stolen(num, slot, func, early_ops);
>  
> +		quirk_applied = true;
> +
>  		return;
>  	}
>  }
> -- 
> 2.34.1
>