[PATCH] drm: Fix DSC BPP increment decoding

[Imre Deak]

On Wed, Feb 12, 2025 at 06:46:40PM +0200, Jani Nikula wrote:
> On Wed, 12 Feb 2025, Imre Deak <imre.deak at intel.com> wrote:
> > Starting with DPCD version 2.0 bits 6:3 of the DP_DSC_BITS_PER_PIXEL_INC
> > DPCD register contains the NativeYCbCr422_MAX_bpp_DELTA field, which can
> > be non-zero as opposed to earlier DPCD versions, hence decoding the
> > bit_per_pixel increment value at bits 2:0 in the same register requires
> > applying a mask, do so.
> >
> > Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> > Fixes: 0c2287c96521 ("drm/display/dp: Add helper function to get DSC bpp precision")
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> 
> Reviewed-by: Jani Nikula <jani.nikula at intel.com>

Thanks, patch is pushed to drm-misc-fixes.

> But we should really clean up the macros:
> 
> #define DP_DSC_BITS_PER_PIXEL_INC           0x06F
> # define DP_DSC_RGB_YCbCr444_MAX_BPP_DELTA_MASK 0x1f
> # define DP_DSC_RGB_YCbCr420_MAX_BPP_DELTA_MASK 0xe0
> 
> These are both for DPCD 0x6e, not 0x6f. They're misleading here. And
> they should contain the /* DP 2.0 */ comment.
> 
> And a similar macro for 0x6f bits 6:3 could be added.

Ok, noted. Decoding and using these caps is still missing, the above
could be fixed when adding that.

> 
> BR,
> Jani.
> 
> 
> > ---
> >  drivers/gpu/drm/display/drm_dp_helper.c | 2 +-
> >  include/drm/display/drm_dp.h            | 1 +
> >  2 files changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> > index c488d160a3c1f..f5c596234729d 100644
> > --- a/drivers/gpu/drm/display/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> > @@ -2602,7 +2602,7 @@ u8 drm_dp_dsc_sink_bpp_incr(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
> >  {
> >  	u8 bpp_increment_dpcd = dsc_dpcd[DP_DSC_BITS_PER_PIXEL_INC - DP_DSC_SUPPORT];
> >  
> > -	switch (bpp_increment_dpcd) {
> > +	switch (bpp_increment_dpcd & DP_DSC_BITS_PER_PIXEL_MASK) {
> >  	case DP_DSC_BITS_PER_PIXEL_1_16:
> >  		return 16;
> >  	case DP_DSC_BITS_PER_PIXEL_1_8:
> > diff --git a/include/drm/display/drm_dp.h b/include/drm/display/drm_dp.h
> > index 784a32bfbad8f..c413ef68f9a30 100644
> > --- a/include/drm/display/drm_dp.h
> > +++ b/include/drm/display/drm_dp.h
> > @@ -359,6 +359,7 @@
> >  # define DP_DSC_BITS_PER_PIXEL_1_4          0x2
> >  # define DP_DSC_BITS_PER_PIXEL_1_2          0x3
> >  # define DP_DSC_BITS_PER_PIXEL_1_1          0x4
> > +# define DP_DSC_BITS_PER_PIXEL_MASK         0x7
> >  
> >  #define DP_PSR_SUPPORT                      0x070   /* XXX 1.2? */
> >  # define DP_PSR_IS_SUPPORTED                1
> 
> -- 
> Jani Nikula, Intel