Re: [PATCH v3 07/16] drm/i915: Fix PTE decode during initial plane readout

[Paz Zcharya <pazz@chromium.org>]

On Tue, Jan 16, 2024 at 11:46:13AM +0100, Nirmoy Das wrote:
> 
> On 1/16/2024 8:56 AM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > When multiple pipes are enabled by the BIOS we try to read out each
> > in turn. But we do the readout for the second only after the inherited
> > vma for the first has been rebound into its original place (and thus
> > the PTEs have been rewritten). Unlike the BIOS we set some high caching
> > bits in the PTE on MTL which confuses the readout for the second plane.
> > Filter out the non-address bits from the PTE value appropriately to
> > fix this.
> > 
> > I suppose it might also be possible that the BIOS would already set
> > some caching bits as well, in which case we'd run into this same
> > issue already for the first plane.
> > 
> > TODO:
> > - should abstract the PTE decoding to avoid details leaking all over
> > - should probably do the readout for all the planes before
> >    we touch anything (including the PTEs) so that we truly read
> >    out the BIOS state
> > 
> > Cc: Paz Zcharya <pazz@chromium.org>
> > Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Acked-by: Nirmoy Das <nirmoy.das@intel.com>

Hi Ville,

Thank you so much for this incredible series.
It solves the issue regarding MTL initial plane readout
that Andrzej Hajda and I worked on in
https://patchwork.freedesktop.org/patch/570811/?series=127130&rev=2
In addition, it solved the issue with the new GOP.

I tested it on two different devices with Meteor Lake and it worked perfectly:
no i915 errors, no flickers or observable issues.

Tested-by: Paz Zcharya <pazz@chromium.org>

> > ---
> >   drivers/gpu/drm/i915/display/intel_plane_initial.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_plane_initial.c b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> > index a55c09cbd0e4..ffc92b18fcf5 100644
> > --- a/drivers/gpu/drm/i915/display/intel_plane_initial.c
> > +++ b/drivers/gpu/drm/i915/display/intel_plane_initial.c
> > @@ -72,7 +72,7 @@ initial_plane_vma(struct drm_i915_private *i915,
> >   			return NULL;
> >   		}
> > -		phys_base = pte & I915_GTT_PAGE_MASK;
> > +		phys_base = pte & GEN12_GGTT_PTE_ADDR_MASK;
> >   		mem = i915->mm.regions[INTEL_REGION_LMEM_0];
> >   		/*