[Intel-gfx] [RFC v5 5/6] drm/i915/dp: Change a link bandwidth computation for DP YCbCr 4:2:0 output

[Gwan-gyeong Mun]

All of the link bandwidth and 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

And it adds missed bpc values for a programming of VSC Header.
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.

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 45 ++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index c5219331539a..40135f98d164 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1823,6 +1823,19 @@ 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,
@@ -1834,8 +1847,10 @@ intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
 	int mode_rate, link_clock, link_avail;
 
 	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) {
+		int output_bpp = intel_dp_output_bpp(pipe_config, bpp);
+
 		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
-						   bpp);
+						   output_bpp);
 
 		for (clock = limits->min_clock; clock <= limits->max_clock; clock++) {
 			for (lane_count = limits->min_lane_count;
@@ -1870,8 +1885,10 @@ intel_dp_compute_link_config_fast(struct intel_dp *intel_dp,
 	int mode_rate, link_clock, link_avail;
 
 	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) {
+		int output_bpp = intel_dp_output_bpp(pipe_config, bpp);
+
 		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
-						   bpp);
+						   output_bpp);
 
 		for (lane_count = limits->min_lane_count;
 		     lane_count <= limits->max_lane_count;
@@ -2220,13 +2237,16 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 			intel_conn_state->broadcast_rgb == INTEL_BROADCAST_RGB_LIMITED;
 	}
 
-	if (!pipe_config->dsc_params.compression_enable)
-		intel_link_compute_m_n(pipe_config->pipe_bpp,
+	if (!pipe_config->dsc_params.compression_enable) {
+		int output_bpp = intel_dp_output_bpp(pipe_config, pipe_config->pipe_bpp);
+
+		intel_link_compute_m_n(output_bpp,
 				       pipe_config->lane_count,
 				       adjusted_mode->crtc_clock,
 				       pipe_config->port_clock,
 				       &pipe_config->dp_m_n,
 				       constant_n);
+	}
 	else
 		intel_link_compute_m_n(pipe_config->dsc_params.compressed_bpp,
 				       pipe_config->lane_count,
@@ -4454,6 +4474,23 @@ intel_pixel_encoding_setup_vsc(struct intel_dp *intel_dp,
 	 * 100b = 16bpc.
 	 */
 	vsc_sdp.DB17 = 0x1;
+	switch (crtc_state->pipe_bpp / 3) {
+	case 8: /* 8bpc */
+		vsc_sdp.DB17 = 0x1;
+		break;
+	case 10: /* 10bpc */
+		vsc_sdp.DB17 = 0x2;
+		break;
+	case 12: /* 12bpc */
+		vsc_sdp.DB17 = 0x3;
+		break;
+	case 16: /* 16bpc */
+		vsc_sdp.DB17 = 0x4;
+		break;
+	default:
+		DRM_DEBUG_KMS("Invalid bpp value '%d'\n", crtc_state->pipe_bpp);
+		break;
+	}
 
 	/*
 	 * Content Type (Bits 2:0)
-- 
2.21.0