Re: [PATCH 12/13] drm/i915/dp: Get optimal link config to have best compressed bpp

["Nautiyal, Ankit K" <ankit.k.nautiyal@xxxxxxxxx>]

Thanks Stan and Ville for the review comments.

I agree can have some documentation about the values used, instead of 
magic numbers.

Also, Ville's approach for dsc_{sink,source}_{min,max}_bpp() seems good, 
and that can be used as helpers in MST case too.

Will add the changes in the next version of the patch.


Thanks & Regards,

Ankit


On 5/16/2023 5:10 PM, Ville Syrjälä wrote:
> On Tue, May 16, 2023 at 01:43:44PM +0300, Lisovskiy, Stanislav wrote:
> > On Fri, May 12, 2023 at 11:54:16AM +0530, Ankit Nautiyal wrote:
> > > Currently, we take the max lane, rate and pipe bpp, to get the maximum
> > > compressed bpp possible. We then set the output bpp to this value.
> > > This patch provides support to have max bpp, min rate and min lanes,
> > > that can support the min compressed bpp.
> > >
> > > v2:
> > > -Avoid ending up with compressed bpp, same as pipe bpp. (Stan)
> > > -Fix the checks for limits->max/min_bpp while iterating over list of
> > >   valid DSC bpcs. (Stan)
> > >
> > > v3:
> > > -Refactor the code to have pipe bpp/compressed bpp computation and slice
> > > count calculation separately for different cases.
> > >
> > > v4:
> > > -Separate the pipe_bpp calculation for eDP and DP.
> > >
> > > Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/i915/display/intel_dp.c | 305 +++++++++++++++++++-----
> > >   1 file changed, 245 insertions(+), 60 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > > index 39e2bf3d738d..578320220c9a 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > > @@ -1642,6 +1642,209 @@ static bool intel_dp_dsc_supports_format(struct intel_dp *intel_dp,
> > >   	return drm_dp_dsc_sink_supports_format(intel_dp->dsc_dpcd, sink_dsc_format);
> > >   }
> > >   
> > > +static bool is_dsc_bw_sufficient(int link_rate, int lane_count, int compressed_bpp,
> > > +				 const struct drm_display_mode *adjusted_mode)
> > > +{
> > > +	int mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock, compressed_bpp);
> > > +	int link_avail = intel_dp_max_data_rate(link_rate, lane_count);
> > > +
> > > +	return mode_rate <= link_avail;
> > > +}
> > > +
> > > +static int dsc_compute_link_config(struct intel_dp *intel_dp,
> > > +				   struct intel_crtc_state *pipe_config,
> > > +				   struct link_config_limits *limits,
> > > +				   int pipe_bpp,
> > > +				   u16 compressed_bpp,
> > > +				   int timeslots)
> > > +{
> > > +	const struct drm_display_mode *adjusted_mode =
> > > +		&pipe_config->hw.adjusted_mode;
> > > +	int link_rate, lane_count;
> > > +	int dsc_max_bpp;
> > > +	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
> > > +	int i;
> > > +
> > > +	for (i = 0; i < intel_dp->num_common_rates; i++) {
> > > +		link_rate = intel_dp_common_rate(intel_dp, i);
> > > +		if (link_rate < limits->min_rate || link_rate > limits->max_rate)
> > > +			continue;
> > > +
> > > +		for (lane_count = limits->min_lane_count;
> > > +		     lane_count <= limits->max_lane_count;
> > > +		     lane_count <<= 1) {
> > > +			dsc_max_bpp = intel_dp_dsc_get_max_compressed_bpp(dev_priv,
> > > +									  link_rate,
> > > +									  lane_count,
> > > +									  adjusted_mode->crtc_clock,
> > > +									  adjusted_mode->crtc_hdisplay,
> > > +									  pipe_config->bigjoiner_pipes,
> > > +									  pipe_config->output_format,
> > > +									  pipe_bpp, timeslots);
> > > +			/*
> > > +			 * According to DSC 1.2a Section 4.1.1 Table 4.1 the maximum
> > > +			 * supported PPS value can be 63.9375 and with the further
> > > +			 * mention that bpp should be programmed double the target bpp
> > > +			 * restricting our target bpp to be 31.9375 at max
> > > +			 */
> > > +			if (pipe_config->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
> > > +				dsc_max_bpp = min_t(u16, dsc_max_bpp, 31);
> > > +
> > > +			if (compressed_bpp > dsc_max_bpp)
> > > +				continue;
> > > +
> > > +			if (!is_dsc_bw_sufficient(link_rate, lane_count,
> > > +						  compressed_bpp, adjusted_mode))
> > > +				continue;
> > > +
> > > +			pipe_config->lane_count = lane_count;
> > > +			pipe_config->port_clock = link_rate;
> > > +
> > > +			return 0;
> > > +		}
> > > +	}
> > > +
> > > +	return -EINVAL;
> > > +}
> > > +
> > > +static
> > > +u16 intel_dp_dsc_max_sink_compressed_bppx16(struct intel_dp *intel_dp,
> > > +					    struct intel_crtc_state *pipe_config,
> > > +					    int bpc)
> > > +{
> > > +	u16 max_bppx16 = drm_edp_dsc_sink_output_bpp(intel_dp->dsc_dpcd);
> > > +
> > > +	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 (3 * bpc) << 4;
> > > +	case INTEL_OUTPUT_FORMAT_YCBCR420:
> > > +		return (3 * (bpc / 2)) << 4;
> > > +	default:
> > > +		MISSING_CASE(pipe_config->output_format);
> > > +		break;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static u16 intel_dp_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 dsc_compute_compressed_bpp(struct intel_dp *intel_dp,
> > > +				      struct intel_crtc_state *pipe_config,
> > > +				      struct link_config_limits *limits,
> > > +				      int pipe_bpp,
> > > +				      int timeslots)
> > > +{
> > > +	struct drm_i915_private *dev_priv = dp_to_i915(intel_dp);
> > > +	u16 compressed_bpp;
> > > +	int dsc_min_bpp, dsc_src_max_bpp, dsc_sink_max_bpp, dsc_max_bpp;
> > > +	int ret;
> > > +
> > > +	dsc_min_bpp = max(intel_dp_dsc_min_compressed_bppx16(pipe_config) >> 4, 8);
> > > +	if (DISPLAY_VER(dev_priv) <= 12)
> > > +		dsc_src_max_bpp = 23;
> > > +	else
> > > +		dsc_src_max_bpp = 27;
> > I would may be added some comment about what are those "23/27" numbers or
> > may be even created some self-explanatory #define constants for those.
> I dislike defines like that. They are single use so don't actually
> do anything in terms of avoiding typoes and other accidental
> mismatches, and people always seem put them in some random place
> (eg. top of file) so then it takes extra work to find them.
>
> The best approach IMO is to just use functions with good names.
> Eg. in this case we could just have a full set of clear functions:
> dsc_{sink,source}_{min,max}_bpp() or something along those line.
>
> > Otherwise in a couple of years, even we ourselves might not be able to recall
> > immediately where those numbers are taken from.
> >
> > Otherwise looks good to me,
> >
> > Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx>
> >
> > > +	dsc_sink_max_bpp =
> > > +		intel_dp_dsc_max_sink_compressed_bppx16(intel_dp,
> > > +							pipe_config, pipe_bpp / 3) >> 4;
> > > +
> > > +	dsc_max_bpp = dsc_sink_max_bpp ? min(dsc_sink_max_bpp, dsc_src_max_bpp) : dsc_src_max_bpp;
> > > +
> > > +	/* Compressed BPP should be less than the Input DSC bpp */
> > > +	dsc_max_bpp = min(dsc_max_bpp, pipe_bpp - 1);
> > > +
> > > +	for (compressed_bpp = dsc_max_bpp;
> > > +	     compressed_bpp >= dsc_min_bpp;
> > > +	     compressed_bpp--) {
> > > +		ret = dsc_compute_link_config(intel_dp,
> > > +					      pipe_config,
> > > +					      limits,
> > > +					      pipe_bpp,
> > > +					      compressed_bpp,
> > > +					      timeslots);
> > > +		if (ret == 0) {
> > > +			pipe_config->dsc.compressed_bpp = compressed_bpp;
> > > +			return 0;
> > > +		}
> > > +	}
> > > +
> > > +	return -EINVAL;
> > > +}
> > > +
> > > +static int intel_dp_dsc_compute_pipe_bpp(struct intel_dp *intel_dp,
> > > +					 struct intel_crtc_state *pipe_config,
> > > +					 struct drm_connector_state *conn_state,
> > > +					 struct link_config_limits *limits,
> > > +					 int timeslots)
> > > +{
> > > +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > > +	u8 dsc_bpc[3] = {0};
> > > +	u8 dsc_max_bpc, dsc_max_bpp;
> > > +	u8 dsc_min_bpc, dsc_min_bpp;
> > > +	u8 max_req_bpc = conn_state->max_requested_bpc;
> > > +	int i, bpp, ret;
> > > +	int num_bpc = drm_dp_dsc_sink_supported_input_bpcs(intel_dp->dsc_dpcd,
> > > +							   dsc_bpc);
> > > +
> > > +	/* Max DSC Input BPC for ICL is 10 and for TGL+ is 12 */
> > > +	if (DISPLAY_VER(i915) >= 12)
> > > +		dsc_max_bpc = min_t(u8, 12, max_req_bpc);
> > > +	else
> > > +		dsc_max_bpc = min_t(u8, 10, max_req_bpc);
> > > +
> > > +	dsc_max_bpp = min(dsc_max_bpc * 3, limits->max_bpp);
> > > +
> > > +	/* Min DSC Input BPC for ICL+ is 8 */
> > > +	dsc_min_bpc = 8;
> > > +	dsc_min_bpp = max(dsc_min_bpc * 3, limits->min_bpp);
> > > +
> > > +	/*
> > > +	 * Get the maximum DSC bpc that will be supported by any valid
> > > +	 * link configuration and compressed bpp.
> > > +	 */
> > > +	for (i = 0; i < num_bpc; i++) {
> > > +		bpp = dsc_bpc[i] * 3;
> > > +
> > > +		if (bpp < dsc_min_bpp)
> > > +			break;
> > > +
> > > +		if (bpp > dsc_max_bpp)
> > > +			continue;
> > > +
> > > +		ret = dsc_compute_compressed_bpp(intel_dp, pipe_config,
> > > +						 limits, bpp, timeslots);
> > > +		if (ret == 0) {
> > > +			pipe_config->pipe_bpp = bpp;
> > > +
> > > +			return 0;
> > > +		}
> > > +	}
> > > +
> > > +	return -EINVAL;
> > > +}
> > > +
> > >   static
> > >   bool is_dsc_pipe_bpp_sufficient(int pipe_bpp)
> > >   {
> > > @@ -1649,6 +1852,31 @@ bool is_dsc_pipe_bpp_sufficient(int pipe_bpp)
> > >   	return (pipe_bpp < 8 * 3);
> > >   }
> > >   
> > > +static int intel_edp_dsc_compute_pipe_bpp(struct intel_dp *intel_dp,
> > > +					  struct intel_crtc_state *pipe_config,
> > > +					  struct drm_connector_state *conn_state,
> > > +					  struct link_config_limits *limits)
> > > +{
> > > +	/* For eDP use max bpp that can be supported with DSC. */
> > > +	int pipe_bpp = intel_dp_dsc_compute_max_bpp(intel_dp,
> > > +						    conn_state->max_requested_bpc);
> > > +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > > +
> > > +	if (!is_dsc_pipe_bpp_sufficient(pipe_bpp)) {
> > > +		drm_dbg_kms(&i915->drm,
> > > +			    "No DSC support for less than 8bpc\n");
> > > +		return -EINVAL;
> > > +	}
> > > +	pipe_config->pipe_bpp = pipe_bpp;
> > > +	pipe_config->port_clock = limits->max_rate;
> > > +	pipe_config->lane_count = limits->max_lane_count;
> > > +	pipe_config->dsc.compressed_bpp =
> > > +		min_t(u16, drm_edp_dsc_sink_output_bpp(intel_dp->dsc_dpcd) >> 4,
> > > +		      pipe_config->pipe_bpp);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >   int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> > >   				struct intel_crtc_state *pipe_config,
> > >   				struct drm_connector_state *conn_state,
> > > @@ -1671,6 +1899,12 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> > >   	if (!intel_dp_dsc_supports_format(intel_dp, pipe_config->output_format))
> > >   		return -EINVAL;
> > >   
> > > +	/*
> > > +	 * compute pipe bpp is set to false for DP MST DSC case
> > > +	 * and compressed_bpp is calculated same time once
> > > +	 * vpci timeslots are allocated, because overall bpp
> > > +	 * calculation procedure is bit different for MST case.
> > > +	 */
> > >   	if (compute_pipe_bpp) {
> > >   		int pipe_bpp;
> > >   		int forced_bpp = intel_dp->force_dsc_bpc * 3;
> > > @@ -1683,31 +1917,25 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> > >   				 forced_bpp && !is_dsc_pipe_bpp_sufficient(forced_bpp),
> > >   				 "Cannot force dsc bpc:%d, due to dsc bpc limits\n",
> > >   				 intel_dp->force_dsc_bpc);
> > > -
> > > -			pipe_bpp = intel_dp_dsc_compute_max_bpp(intel_dp,
> > > -								conn_state->max_requested_bpc);
> > > -
> > > -			if (!is_dsc_pipe_bpp_sufficient(pipe_bpp)) {
> > > -				drm_dbg_kms(&dev_priv->drm, "No DSC support for less than 8bpc\n");
> > > -				return -EINVAL;
> > > +			if (intel_dp_is_edp(intel_dp))
> > > +				ret = intel_edp_dsc_compute_pipe_bpp(intel_dp, pipe_config,
> > > +								     conn_state, limits);
> > > +			else
> > > +				ret = intel_dp_dsc_compute_pipe_bpp(intel_dp, pipe_config,
> > > +								    conn_state, limits, timeslots);
> > > +			if (ret) {
> > > +				drm_dbg_kms(&dev_priv->drm,
> > > +					    "No Valid pipe bpp for given mode ret = %d\n", ret);
> > > +				return ret;
> > >   			}
> > >   		}
> > > -
> > > -		pipe_config->pipe_bpp = pipe_bpp;
> > >   	}
> > >   
> > > -	/*
> > > -	 * For now enable DSC for max link rate, max lane count.
> > > -	 * Optimize this later for the minimum possible link rate/lane count
> > > -	 * with DSC enabled for the requested mode.
> > > -	 */
> > >   	pipe_config->port_clock = limits->max_rate;
> > >   	pipe_config->lane_count = limits->max_lane_count;
> > >   
> > > +	/* Calculate Slice count */
> > >   	if (intel_dp_is_edp(intel_dp)) {
> > > -		pipe_config->dsc.compressed_bpp =
> > > -			min_t(u16, drm_edp_dsc_sink_output_bpp(intel_dp->dsc_dpcd) >> 4,
> > > -			      pipe_config->pipe_bpp);
> > >   		pipe_config->dsc.slice_count =
> > >   			drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
> > >   							true);
> > > @@ -1717,37 +1945,8 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> > >   			return -EINVAL;
> > >   		}
> > >   	} else {
> > > -		u16 dsc_max_compressed_bpp = 0;
> > >   		u8 dsc_dp_slice_count;
> > >   
> > > -		if (compute_pipe_bpp) {
> > > -			dsc_max_compressed_bpp =
> > > -				intel_dp_dsc_get_max_compressed_bpp(dev_priv,
> > > -								    pipe_config->port_clock,
> > > -								    pipe_config->lane_count,
> > > -								    adjusted_mode->crtc_clock,
> > > -								    adjusted_mode->crtc_hdisplay,
> > > -								    pipe_config->bigjoiner_pipes,
> > > -								    pipe_config->output_format,
> > > -								    pipe_config->pipe_bpp,
> > > -								    timeslots);
> > > -			/*
> > > -			 * According to DSC 1.2a Section 4.1.1 Table 4.1 the maximum
> > > -			 * supported PPS value can be 63.9375 and with the further
> > > -			 * mention that bpp should be programmed double the target bpp
> > > -			 * restricting our target bpp to be 31.9375 at max
> > > -			 */
> > > -			if (pipe_config->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
> > > -				dsc_max_compressed_bpp = min_t(u16,
> > > -							       dsc_max_compressed_bpp,
> > > -							       31);
> > > -
> > > -			if (!dsc_max_compressed_bpp) {
> > > -				drm_dbg_kms(&dev_priv->drm,
> > > -					    "Compressed BPP not supported\n");
> > > -				return -EINVAL;
> > > -			}
> > > -		}
> > >   		dsc_dp_slice_count =
> > >   			intel_dp_dsc_get_slice_count(intel_dp,
> > >   						     adjusted_mode->crtc_clock,
> > > @@ -1759,20 +1958,6 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> > >   			return -EINVAL;
> > >   		}
> > >   
> > > -		/*
> > > -		 * compute pipe bpp is set to false for DP MST DSC case
> > > -		 * and compressed_bpp is calculated same time once
> > > -		 * vpci timeslots are allocated, because overall bpp
> > > -		 * calculation procedure is bit different for MST case.
> > > -		 */
> > > -		if (compute_pipe_bpp) {
> > > -			u16 output_bpp = intel_dp_output_bpp(pipe_config->output_format,
> > > -							     pipe_config->pipe_bpp);
> > > -
> > > -			pipe_config->dsc.compressed_bpp = min_t(u16,
> > > -								dsc_max_compressed_bpp,
> > > -								output_bpp);
> > > -		}
> > >   		pipe_config->dsc.slice_count = dsc_dp_slice_count;
> > >   	}
> > >   	/*
> > > --
> > > 2.25.1