Re: [Intel-gfx] [PATCH v11 06/11] drm/i915/dp: Consider output_format while computing dsc bpp for mode_valid

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

On Mon, Mar 20, 2023 at 09:06:25AM +0530, Nautiyal, Ankit K wrote:
> 
> On 3/17/2023 6:30 AM, Ville Syrjälä wrote:
> > On Tue, Mar 14, 2023 at 04:34:10PM +0530, Ankit Nautiyal wrote:
> >> During modevalid step, the pipe bpp is computed assuming RGB output
> >> format. When checking with DSC, consider the output_format and compute
> >> the input bpp for DSC appropriately.
> >>
> >> v2: For DP-MST we currently use RGB output format only, so continue
> >> using RGB while computing dsc_bpp for MST case.
> >>
> >> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/display/intel_dp.c     | 28 ++++++++++++++++-----
> >>   drivers/gpu/drm/i915/display/intel_dp.h     |  4 ++-
> >>   drivers/gpu/drm/i915/display/intel_dp_mst.c |  2 +-
> >>   3 files changed, 26 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> >> index dcb3c2519041..499390c519ca 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> >> @@ -1110,11 +1110,21 @@ intel_dp_mode_valid(struct drm_connector *_connector,
> >>   
> >>   	if (HAS_DSC(dev_priv) &&
> >>   	    drm_dp_sink_supports_dsc(intel_dp->dsc_dpcd)) {
> >> +		int pipe_bpp;
> >> +		enum intel_output_format output_format, sink_format;
> >> +		const struct drm_display_info *info = &connector->base.display_info;
> >> +
> >> +		if (	(info, mode))
> >> +			sink_format = INTEL_OUTPUT_FORMAT_YCBCR420;
> >> +		else
> >> +			sink_format = INTEL_OUTPUT_FORMAT_RGB;
> > I think I saw this same code duplicated somewhere else already.
> > Time for a intel_dp_sink_format()?
> 
> Yes this can be made as a common function, also used in 
> intel_dp_mode_min_output_bpp.
> 
> Will add the helper intel_dp_sink_format for this.
> 
> >
> >> +
> >> +		output_format = intel_dp_output_format(connector, sink_format);
> >>   		/*
> >>   		 * TBD pass the connector BPC,
> >>   		 * for now U8_MAX so that max BPC on that platform would be picked
> >>   		 */
> >> -		int pipe_bpp = intel_dp_dsc_compute_bpp(intel_dp, U8_MAX);
> >> +		pipe_bpp = intel_dp_dsc_compute_bpp(intel_dp, output_format, U8_MAX);
> >>   
> >>   		/*
> >>   		 * Output bpp is stored in 6.4 format so right shift by 4 to get the
> >> @@ -1454,12 +1464,15 @@ intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
> >>   	return -EINVAL;
> >>   }
> >>   
> >> -int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp, u8 max_req_bpc)
> >> +int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp,
> >> +			     enum intel_output_format output_format,
> >> +			     u8 max_req_bpc)
> >>   {
> >>   	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >>   	int i, num_bpc;
> >>   	u8 dsc_bpc[3] = {0};
> >>   	u8 dsc_max_bpc;
> >> +	int pipe_bpp = 0;
> >>   
> >>   	/* Max DSC Input BPC for ICL is 10 and for TGL+ is 12 */
> >>   	if (DISPLAY_VER(i915) >= 12)
> >> @@ -1470,11 +1483,13 @@ int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp, u8 max_req_bpc)
> >>   	num_bpc = drm_dp_dsc_sink_supported_input_bpcs(intel_dp->dsc_dpcd,
> >>   						       dsc_bpc);
> >>   	for (i = 0; i < num_bpc; i++) {
> >> -		if (dsc_max_bpc >= dsc_bpc[i])
> >> -			return dsc_bpc[i] * 3;
> >> +		if (dsc_max_bpc >= dsc_bpc[i]) {
> >> +			pipe_bpp = dsc_bpc[i] * 3;
> >> +			break;
> >> +		}
> >>   	}
> >>   
> >> -	return 0;
> >> +	return intel_dp_output_bpp(output_format, pipe_bpp);
> > The pipe_bpp vs. output_bpp terms seem a bit confused now in the dsc
> > code.
> >
> > In the non-compressed cases pipe_bpp does not include any
> > subsampling, output_bpp is the subsampled version.
> >
> > What this dsc code seems to want is an intermediate value which
> > is the subsampled pipe_bpp that is the input to dsc compressor?
> > And output_bpp/dsc.compressed_bpp is then the final bpp coming
> > out of the compressor.
> 
> 
> Yes I now realize, this is wrong, it should have been pipe_bpp not the 
> subsampled pipe_bpp.
> 
> As I understand, we are using subsampled pipe_bpp only to compute the 
> bandwidth/clock checks.
> 
> You are right, we need use pipe_bpp for programming, and the same is 
> input to DSC, and not the subsampled pipe_bpp.
> 
> I Will remove this line from the function.
> 
> >
> > I think we should invent a consistent set of names for each so that
> > it's clear which value the code is concerned with.
> 
> Yes you are right output_bpp is used as compressed_bpp in some places, 
> functions.
> 
> We can go with something like this perhaps:
> 
> pipe_bpp : the actual bits_per_pixel, that we program
> 
> output_bpp : In case of YcbCr420,422 output format bytes_per_pixel will 
> be half the number of bytes of RGB pixel.
> 
> compressed_bpp : (Only for DSC case) the target BPP for the DSC encoder, 
> after compression.
> 
> Does this make sense? I can try to have a separate patch for this.

Then I think we need a new name for the final bpp in
intel_dp_compute_config() at least. Hmm, maybe link_bpp?
intel_dp_compute_link_config_wide() should perhaps use that
same name as well.

> 
> 
> >>   }
> >>   
> >>   static int intel_dp_source_dsc_version_minor(struct intel_dp *intel_dp)
> >> @@ -1588,7 +1603,8 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> >>   		return -EINVAL;
> >>   
> >>   	if (compute_pipe_bpp)
> >> -		pipe_bpp = intel_dp_dsc_compute_bpp(intel_dp, conn_state->max_requested_bpc);
> >> +		pipe_bpp = intel_dp_dsc_compute_bpp(intel_dp, pipe_config->output_format,
> >> +						    conn_state->max_requested_bpc);
> > This pipe_bpp gets plugged back into crtc_state->pipe_bpp later and
> > then it'll be the subsampled version. I don't think that is what we want
> > eg. for dithering setup and whatnot.
> 
> You  are right, this is incorrect. Removing the line as mentioned above 
> will fix this.
> 
> Thanks for pointing out this issue. I will fix this in next version of 
> the patch.
> 
> 
> Regards,
> 
> Ankit
> 
> >
> >>   	else
> >>   		pipe_bpp = pipe_config->pipe_bpp;
> >>   
> >> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> >> index ef39e4f7a329..2f4136e43f38 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> >> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> >> @@ -102,7 +102,9 @@ void intel_read_dp_sdp(struct intel_encoder *encoder,
> >>   		       struct intel_crtc_state *crtc_state,
> >>   		       unsigned int type);
> >>   bool intel_digital_port_connected(struct intel_encoder *encoder);
> >> -int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp, u8 dsc_max_bpc);
> >> +int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp,
> >> +			     enum intel_output_format output_format,
> >> +			     u8 dsc_max_bpc);
> >>   u16 intel_dp_dsc_get_output_bpp(struct drm_i915_private *i915,
> >>   				u32 link_clock, u32 lane_count,
> >>   				u32 mode_clock, u32 mode_hdisplay,
> >> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> >> index ff0b821a901a..bdc5c53ccd75 100644
> >> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> >> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> >> @@ -917,7 +917,7 @@ intel_dp_mst_mode_valid_ctx(struct drm_connector *connector,
> >>   		 * TBD pass the connector BPC,
> >>   		 * for now U8_MAX so that max BPC on that platform would be picked
> >>   		 */
> >> -		int pipe_bpp = intel_dp_dsc_compute_bpp(intel_dp, U8_MAX);
> >> +		int pipe_bpp = intel_dp_dsc_compute_bpp(intel_dp, INTEL_OUTPUT_FORMAT_RGB, U8_MAX);
> >>   
> >>   		if (drm_dp_sink_supports_fec(intel_dp->fec_capable)) {
> >>   			dsc_max_output_bpp =
> >> -- 
> >> 2.25.1

-- 
Ville Syrjälä
Intel