Re: [Intel-gfx] [PATCH] drm/i915: Query compressed bpp properly using correct DPCD and DP Spec info

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Apr 06, 2023 at 12:59:40PM +0300, Jani Nikula wrote:
> On Thu, 06 Apr 2023, Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> wrote:
> > Currently we seem to be using wrong DPCD register for reading compressed bpps,
> > reading min/max input bpc instead of compressed bpp.
> > Fix that, so that we now apply min/max compressed bpp limitations we get
> > from DP Spec Table 2-157 DP v2.0 and/or correspondent DPCD register
> > DP_DSC_MAX_BITS_PER_PIXEL_LOW/HIGH.
> >
> > This might also allow us to get rid of an ugly compressed bpp recalculation,
> > which we had to add to make some MST hubs usable.
> >
> > Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp_mst.c | 76 ++++++++++++++-------
> >  1 file changed, 52 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > index a88b852c437c..9479c7e0b269 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > @@ -174,6 +174,50 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
> >  	return 0;
> >  }
> >  
> > +static u16 dsc_max_sink_compressed_bppx16(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
> > +					  struct intel_crtc_state *pipe_config,
> > +					  int bpc)
> > +{
> > +	u16 max_bppx16 = dsc_dpcd[DP_DSC_MAX_BITS_PER_PIXEL_LOW - DP_DSC_SUPPORT] |
> > +			 (dsc_dpcd[DP_DSC_MAX_BITS_PER_PIXEL_HI - DP_DSC_SUPPORT] &
> > +			  DP_DSC_MAX_BITS_PER_PIXEL_HI_MASK << DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT);
> 
> This duplicates drm_edp_dsc_sink_output_bpp().

These registers are not even valid for non-eDP.

> 
> Both have operator precedence wrong, leading to the high byte always
> being ignored. For example, sink reported max bpp of 32 turns to 0, and
> 24 turns to 8.
> 
> Broken since 2018. 0575650077ea ("drm/dp: DRM DP helper/macros to get DP
> sink DSC parameters").
> 
> The definition of DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT is misleading wrt
> all of our regular usage. We should never have a FOO_MASK << FOO_SHIFT
> in code, the MASK should always be already shifted in place. Here we do,
> because the shift is not for shifting the mask in place, it's for
> combining the high and low bytes. But I don't really think
> DP_DSC_MAX_BITS_PER_PIXEL_HI_SHIFT should exist, at all.
> 
> BR,
> Jani.
> 
> 
> 
> > +
> > +	if (max_bppx16)
> > +		return max_bppx16;
> > +	/*
> > +	 * If support not given in DPCD 67h, 68h use the Maximum Allowed bit rate
> > +	 * values as given in spec Table 2-157 DP v2.0
> > +	 */
> > +	switch (pipe_config->output_format) {
> > +	case INTEL_OUTPUT_FORMAT_RGB:
> > +	case INTEL_OUTPUT_FORMAT_YCBCR444:
> > +		return bpc << 4;
> > +	case INTEL_OUTPUT_FORMAT_YCBCR420:
> > +		return (3 * (bpc / 2)) << 4;
> > +	default:
> > +		MISSING_CASE(pipe_config->output_format);
> > +		break;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static u16 dsc_min_compressed_bppx16(struct intel_crtc_state *pipe_config)
> > +{
> > +	switch (pipe_config->output_format) {
> > +	case INTEL_OUTPUT_FORMAT_RGB:
> > +	case INTEL_OUTPUT_FORMAT_YCBCR444:
> > +		return 8 << 4;
> > +	case INTEL_OUTPUT_FORMAT_YCBCR420:
> > +		return 6 << 4;
> > +	default:
> > +		MISSING_CASE(pipe_config->output_format);
> > +		break;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
> >  						struct intel_crtc_state *crtc_state,
> >  						struct drm_connector_state *conn_state,
> > @@ -191,8 +235,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
> >  	u8 dsc_bpc[3] = {0};
> >  	int min_bpp, max_bpp, sink_min_bpp, sink_max_bpp;
> >  	u8 dsc_max_bpc;
> > -	bool need_timeslot_recalc = false;
> > -	u32 last_compressed_bpp;
> >  
> >  	/* Max DSC Input BPC for ICL is 10 and for TGL+ is 12 */
> >  	if (DISPLAY_VER(i915) >= 12)
> > @@ -228,6 +270,14 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
> >  	if (max_bpp > sink_max_bpp)
> >  		max_bpp = sink_max_bpp;
> >  
> > +	/* Get Min/Max compressed bpp's for those Input Bpps we got for source/sink */
> > +	max_bpp = min(max_bpp, dsc_max_sink_compressed_bppx16(intel_dp->dsc_dpcd, crtc_state, max_bpp / 3) >> 4);
> > +	min_bpp = max(min_bpp, dsc_min_compressed_bppx16(crtc_state) >> 4);
> > +
> > +	/* Align compressed bpps according to our own constraints */
> > +	max_bpp = intel_dp_dsc_nearest_valid_bpp(i915, max_bpp, crtc_state->pipe_bpp);
> > +	min_bpp = intel_dp_dsc_nearest_valid_bpp(i915, min_bpp, crtc_state->pipe_bpp);
> > +
> >  	slots = intel_dp_mst_find_vcpi_slots_for_bpp(encoder, crtc_state, max_bpp,
> >  						     min_bpp, limits,
> >  						     conn_state, 2 * 3, true);
> > @@ -235,28 +285,6 @@ static int intel_dp_dsc_mst_compute_link_config(struct intel_encoder *encoder,
> >  	if (slots < 0)
> >  		return slots;
> >  
> > -	last_compressed_bpp = crtc_state->dsc.compressed_bpp;
> > -
> > -	crtc_state->dsc.compressed_bpp = intel_dp_dsc_nearest_valid_bpp(i915,
> > -									last_compressed_bpp,
> > -									crtc_state->pipe_bpp);
> > -
> > -	if (crtc_state->dsc.compressed_bpp != last_compressed_bpp)
> > -		need_timeslot_recalc = true;
> > -
> > -	/*
> > -	 * Apparently some MST hubs dislike if vcpi slots are not matching precisely
> > -	 * the actual compressed bpp we use.
> > -	 */
> > -	if (need_timeslot_recalc) {
> > -		slots = intel_dp_mst_find_vcpi_slots_for_bpp(encoder, crtc_state,
> > -							     crtc_state->dsc.compressed_bpp,
> > -							     crtc_state->dsc.compressed_bpp,
> > -							     limits, conn_state, 2 * 3, true);
> > -		if (slots < 0)
> > -			return slots;
> > -	}
> > -
> >  	intel_link_compute_m_n(crtc_state->dsc.compressed_bpp,
> >  			       crtc_state->lane_count,
> >  			       adjusted_mode->crtc_clock,
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Ville Syrjälä
Intel