[PATCH v8 5/6] drm/i915/dp: Change a link bandwidth computation for DP

[Gwan-gyeong Mun]

Data M/N calculations were assumed a bpp as RGB format. But when we are
using YCbCr 4:2:0 output format on DP, we should change bpp calculations
as YCbCr 4:2:0 format. The pipe_bpp value was assumed RGB format,
therefore, it was multiplied with 3. But YCbCr 4:2:0 requires a multiplier
value to 1.5.
Therefore we need to divide pipe_bpp to 2 while DP output uses YCbCr4:2:0
format.
 - RGB format bpp = bpc x 3
 - YCbCr 4:2:0 format bpp = bpc x 1.5

But Link M/N values are calculated and applied based on the Full Clock for
YCbCr 4:2:0. And DP YCbCr 4:2:0 does not need to pixel clock double for
a dotclock caluation. Only for HDMI YCbCr 4:2:0 needs to pixel clock double
for a dot clock calculation.

It only affects dp and edp port which use YCbCr 4:2:0 output format.
And for now, it does not consider a use case of DSC + YCbCr 4:2:0.

v2:
  Addressed review comments from Ville.
  Remove a changing of pipe_bpp on intel_ddi_set_pipe_settings().
  Because the pipe is running at the full bpp, keep pipe_bpp as RGB
  even though YCbCr 4:2:0 output format is used.
  Add a link bandwidth computation for YCbCr4:2:0 output format.

v3:
  Addressed reivew comments from Ville.
  In order to make codes simple, it adds and uses intel_dp_output_bpp()
  function.

v6:
  Link M/N values are calculated and applied based on the Full Clock for
  YCbCr420. The Bit per Pixel needs to be adjusted for YUV420 mode as it
  requires only half of the RGB case.
    - Link M/N values are calculated and applied based on the Full Clock
    - Data M/N values needs to be calculated considering the data is half
      due to subsampling
  Remove a doubling of pixel clock on a dot clock calculator for
  DP YCbCr 4:2:0.
  Rebase and remove a duplicate setting of vsc_sdp.DB17.
  Add a setting of dynamic range bit to  vsc_sdp.DB17.
  Change Content Type bit to "Graphics" from "Not defined".
  Change a dividing of pipe_bpp to muliplying to constant values on a
  switch-case statement.

v7:
  Addressed review comments from Ville.
  Move a setting of dynamic range bit and a setting of bpc which is based
  on pipe_bpp to a "drm/i915/dp: Program VSC Header and DB for Pixel
  Encoding/Colorimetry Format" commit.
  Change Content Type bit to "Not defined" from "Graphics".

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c |  3 ++-
 drivers/gpu/drm/i915/intel_dp.c  | 15 ++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 3f247f091d4c..df06e5bb4764 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1457,7 +1457,8 @@ static void ddi_dotclock_get(struct intel_crtc_state *pipe_config)
 	else
 		dotclock = pipe_config->port_clock;
 
-	if (pipe_config->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
+	if (pipe_config->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 &&
+	    !intel_crtc_has_dp_encoder(pipe_config))
 		dotclock *= 2;
 
 	if (pipe_config->pixel_multiplier)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 6f3c024b9d33..5a614c345fac 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1850,6 +1850,19 @@ intel_dp_adjust_compliance_config(struct intel_dp *intel_dp,
 	}
 }
 
+static int intel_dp_output_bpp(const struct intel_crtc_state *crtc_state, int bpp)
+{
+	/*
+	 * bpp value was assumed to RGB format. And YCbCr 4:2:0 output
+	 * format of the number of bytes per pixel will be half the number
+	 * of bytes of RGB pixel.
+	 */
+	if (crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
+		bpp /= 2;
+
+	return bpp;
+}
+
 /* Optimize link config in order: max bpp, min clock, min lanes */
 static int
 intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
@@ -2223,7 +2236,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 	if (pipe_config->dsc_params.compression_enable)
 		output_bpp = pipe_config->dsc_params.compressed_bpp;
 	else
-		output_bpp = pipe_config->pipe_bpp;
+		output_bpp = intel_dp_output_bpp(pipe_config, pipe_config->pipe_bpp);
 
 	intel_link_compute_m_n(output_bpp,
 			       pipe_config->lane_count,
-- 
2.21.0