Re: [PATCH 03/50] drm/i915/dp: Fix DSC sink's slice count capability check

[Imre Deak <imre.deak@intel.com>]

On Tue, Dec 09, 2025 at 10:51:10AM +0200, Luca Coelho wrote:
> On Thu, 2025-11-27 at 19:49 +0200, Imre Deak wrote:
> > A DSC sink supporting DSC slice count N, not necessarily supports slice
> > counts less than N. Hence the driver should check the sink's support for
> > a particular slice count before using that slice count, fix
> > intel_dp_dsc_get_slice_count() accordingly.
> > 
> > Cc: dri-devel@lists.freedesktop.org
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 18 +++++++++++++-----
> >  1 file changed, 13 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 0ec82fcbcf48e..6d232c15a0b5a 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -1013,6 +1013,8 @@ u8 intel_dp_dsc_get_slice_count(const struct intel_connector *connector,
> >  				int num_joined_pipes)
> >  {
> >  	struct intel_display *display = to_intel_display(connector);
> > +	u32 sink_slice_count_mask =
> > +		drm_dp_dsc_sink_slice_count_mask(connector->dp.dsc_dpcd, false);
> >  	u8 min_slice_count, i;
> >  	int max_slice_width;
> >  	int tp_rgb_yuv444;
> > @@ -1084,9 +1086,9 @@ u8 intel_dp_dsc_get_slice_count(const struct intel_connector *connector,
> >  		    (!HAS_DSC_3ENGINES(display) || num_joined_pipes != 4))
> >  			continue;
> >  
> > -		if (test_slice_count >
> > -		    drm_dp_dsc_sink_max_slice_count(connector->dp.dsc_dpcd, false))
> > -			break;
> > +		if (!(drm_dp_dsc_slice_count_to_mask(test_slice_count) &
> > +		      sink_slice_count_mask))
> > +			continue;
> >  
> >  		 /*
> >  		  * Bigjoiner needs small joiner to be enabled.
> > @@ -1103,8 +1105,14 @@ u8 intel_dp_dsc_get_slice_count(const struct intel_connector *connector,
> >  			return test_slice_count;
> >  	}
> >  
> > -	drm_dbg_kms(display->drm, "Unsupported Slice Count %d\n",
> > -		    min_slice_count);
> > +	/* Print slice count 1,2,4,..24 if bit#0,1,3,..23 is set in the mask. */
> > +	sink_slice_count_mask <<= 1;
> > +	drm_dbg_kms(display->drm,
> > +		    "[CONNECTOR:%d:%s] Unsupported slice count (min: %d, sink supported: %*pbl)\n",
> > +		    connector->base.base.id, connector->base.name,
> > +		    min_slice_count,
> > +		    (int)BITS_PER_TYPE(sink_slice_count_mask), &sink_slice_count_mask);
> > +
> >  	return 0;
> >  }
> > 
> 
> I think this patch could be squashed into the previous one.  IMHO it
> makes it a bit easier to see how those functions defined in the
> previous patch would be used.

The practice I follow is to keep the DRM core and driver changes in
separate patches. At least one reason for that is that the DRM core
patches may need to be applied to the DRM core trees separately.

> But nevertheless:
> 
> Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
> 
> --
> Cheers,
> Luca.