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

[Rodrigo Vivi]

On Fri, Jan 07, 2022 at 08:57:32PM -0600, Bjorn Helgaas wrote:
> 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 at 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.


Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>

Bjorn, ack to merge through drm-intel?


> 
> > ---
> > 
> > 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
> >