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

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Thu, Apr 06, 2023 at 01:56:00PM +0300, Ville Syrjälä wrote:
> 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.

BTW just checked DP 2.0 spec, says "For DP v2.0 (and higher) and eDP v1.4a (and higher)"
for registers 0x67, 0x68.

Otherwise if those are cleared and for older DP/eDP standards it instruct to use Table 2-154.

So I guess this function can be used still.

Stan

> 
> > 
> > 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