Re: [PATCH 14/16] drm/i915/dp: Account for DSC slice overhead

[Imre Deak <imre.deak@intel.com>]

On Thu, Jan 29, 2026 at 10:41:52PM +0530, Ankit Nautiyal wrote:
> Account for DSC slice overhead bubbles and adjust the pixel rate while
> checking the pixel rate against the max dotclock limits.
> 
> v2: Add missing assignment for dsc_slice_count in
> mst_connector_mode_valid_ctx(). (Imre)
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c     | 20 ++++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_dp.h     |  2 ++
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 19 +++++++++++++++++++
>  drivers/gpu/drm/i915/display/intel_vdsc.c   |  1 -
>  drivers/gpu/drm/i915/display/intel_vdsc.h   |  3 +++
>  5 files changed, 44 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 69a87c5933b1..798a0d192b72 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1414,6 +1414,8 @@ bool intel_dp_can_join(struct intel_display *display,
>  
>  bool intel_dp_dotclk_valid(struct intel_display *display,
>  			   int target_clock,
> +			   int htotal,
> +			   int dsc_slice_count,
>  			   int num_joined_pipes)
>  {
>  	int max_dotclk = display->cdclk.max_dotclk_freq;
> @@ -1421,6 +1423,12 @@ bool intel_dp_dotclk_valid(struct intel_display *display,
>  
>  	effective_dotclk_limit = max_dotclk * num_joined_pipes;
>  
> +	if (dsc_slice_count)
> +		target_clock = intel_dsc_get_pixel_rate_with_dsc_bubbles(display,
> +									 target_clock,
> +									 htotal,
> +									 dsc_slice_count);
> +
>  	return target_clock <= effective_dotclk_limit;
>  }
>  
> @@ -1553,8 +1561,13 @@ intel_dp_mode_valid(struct drm_connector *_connector,
>  		if (status != MODE_OK)
>  			continue;
>  
> +		if (!dsc)
> +			dsc_slice_count = 0;
> +
>  		if (!intel_dp_dotclk_valid(display,
>  					   target_clock,
> +					   mode->htotal,
> +					   dsc_slice_count,
>  					   num_joined_pipes))
>  			continue;
>  
> @@ -2787,6 +2800,7 @@ intel_dp_compute_link_for_joined_pipes(struct intel_encoder *encoder,
>  	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>  	struct link_config_limits limits;
>  	bool dsc_needed, joiner_needs_dsc;
> +	int dsc_slice_count = 0;
>  	int ret = 0;
>  
>  	joiner_needs_dsc = intel_dp_joiner_needs_dsc(display, num_joined_pipes);
> @@ -2815,6 +2829,8 @@ intel_dp_compute_link_for_joined_pipes(struct intel_encoder *encoder,
>  		if (ret ||
>  		    !intel_dp_dotclk_valid(display,
>  					   adjusted_mode->crtc_clock,
> +					   adjusted_mode->crtc_htotal,
> +					   dsc_slice_count,

Nit: It's odd to pass dsc_slice_count instead of a literal 0 in this
uncompressed case. The variable could be then also better scoped. The
same applies to mst_stream_compute_link_for_joined_pipes().

Regardless of the above:
Reviewed-by: Imre Deak <imre.deak@intel.com>

>  					   num_joined_pipes))
>  			dsc_needed = true;
>  	}
> @@ -2841,8 +2857,12 @@ intel_dp_compute_link_for_joined_pipes(struct intel_encoder *encoder,
>  		if (ret < 0)
>  			return ret;
>  
> +		dsc_slice_count = intel_dsc_line_slice_count(&pipe_config->dsc.slice_config);
> +
>  		if (!intel_dp_dotclk_valid(display,
>  					   adjusted_mode->crtc_clock,
> +					   adjusted_mode->crtc_htotal,
> +					   dsc_slice_count,
>  					   num_joined_pipes))
>  			return -EINVAL;
>  	}
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index edeb09372d1e..95a38763a367 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -226,6 +226,8 @@ bool intel_dp_can_join(struct intel_display *display,
>  		       int num_joined_pipes);
>  bool intel_dp_dotclk_valid(struct intel_display *display,
>  			   int target_clock,
> +			   int htotal,
> +			   int dsc_slice_count,
>  			   int num_joined_pipes);
>  
>  #endif /* __INTEL_DP_H__ */
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 129ea3e3916e..1c4b3014ba33 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -608,6 +608,7 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>  		to_intel_connector(conn_state->connector);
>  	struct link_config_limits limits;
>  	bool dsc_needed, joiner_needs_dsc;
> +	int dsc_slice_count = 0;
>  	int ret = 0;
>  
>  	joiner_needs_dsc = intel_dp_joiner_needs_dsc(display, num_joined_pipes);
> @@ -626,6 +627,8 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>  		if (ret ||
>  		    !intel_dp_dotclk_valid(display,
>  					   adjusted_mode->clock,
> +					   adjusted_mode->htotal,
> +					   dsc_slice_count,
>  					   num_joined_pipes))
>  			dsc_needed = true;
>  	}
> @@ -670,8 +673,12 @@ static int mst_stream_compute_link_for_joined_pipes(struct intel_encoder *encode
>  		if (ret)
>  			return ret;
>  
> +		dsc_slice_count = intel_dp_mst_dsc_get_slice_count(connector, pipe_config);
> +
>  		if (!intel_dp_dotclk_valid(display,
>  					   adjusted_mode->clock,
> +					   adjusted_mode->htotal,
> +					   dsc_slice_count,
>  					   num_joined_pipes))
>  			return -EINVAL;
>  	}
> @@ -1531,6 +1538,8 @@ mst_connector_mode_valid_ctx(struct drm_connector *_connector,
>  	}
>  
>  	for (num_pipes = 1; num_pipes <= I915_MAX_PIPES; num_pipes++) {
> +		int dsc_slice_count = 0;
> +
>  		*status = MODE_CLOCK_HIGH;
>  
>  		if (connector->force_joined_pipes &&
> @@ -1553,6 +1562,11 @@ mst_connector_mode_valid_ctx(struct drm_connector *_connector,
>  			 */
>  			int pipe_bpp = intel_dp_dsc_compute_max_bpp(connector, U8_MAX);
>  
> +			dsc_slice_count = intel_dp_dsc_get_slice_count(connector,
> +								       mode->clock,
> +								       mode->hdisplay,
> +								       num_joined_pipes);
> +
>  			if (!drm_dp_is_uhbr_rate(max_link_clock))
>  				bw_overhead_flags |= DRM_DP_BW_OVERHEAD_FEC;
>  
> @@ -1575,8 +1589,13 @@ mst_connector_mode_valid_ctx(struct drm_connector *_connector,
>  		if (*status != MODE_OK)
>  			continue;
>  
> +		if (!dsc)
> +			dsc_slice_count = 0;
> +
>  		if (!intel_dp_dotclk_valid(display,
>  					   mode->clock,
> +					   mode->htotal,
> +					   dsc_slice_count,
>  					   num_joined_pipes))
>  			*status = MODE_CLOCK_HIGH;
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c b/drivers/gpu/drm/i915/display/intel_vdsc.c
> index 642a89270d8e..7e53201b3cb1 100644
> --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
> @@ -1104,7 +1104,6 @@ void intel_vdsc_state_dump(struct drm_printer *p, int indent,
>  	drm_dsc_dump_config(p, indent, &crtc_state->dsc.config);
>  }
>  
> -static
>  int intel_dsc_get_pixel_rate_with_dsc_bubbles(struct intel_display *display,
>  					      int pixel_rate, int htotal,
>  					      int dsc_horizontal_slices)
> diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.h b/drivers/gpu/drm/i915/display/intel_vdsc.h
> index aeb17670307b..f4d5b37293cf 100644
> --- a/drivers/gpu/drm/i915/display/intel_vdsc.h
> +++ b/drivers/gpu/drm/i915/display/intel_vdsc.h
> @@ -41,5 +41,8 @@ void intel_vdsc_state_dump(struct drm_printer *p, int indent,
>  			   const struct intel_crtc_state *crtc_state);
>  int intel_vdsc_min_cdclk(const struct intel_crtc_state *crtc_state);
>  unsigned int intel_vdsc_prefill_lines(const struct intel_crtc_state *crtc_state);
> +int intel_dsc_get_pixel_rate_with_dsc_bubbles(struct intel_display *display,
> +					      int pixel_rate, int htotal,
> +					      int dsc_horizontal_slices);
>  
>  #endif /* __INTEL_VDSC_H__ */
> -- 
> 2.45.2
>