[PATCH] drm/amd/display: add a check for display depth validity

[mikita.lipski at amd.com]

From: Mikita Lipski <mikita.lipski at amd.com>

[why]
HDMI 2.0 fails to validate 4K at 60 timing with 10 bpc
[how]
Adding a helper function that would verify if the display depth
assigned would pass a bandwidth validation.
Drop the display depth by one level till calculated pixel clk
is lower than maximum TMDS clk.

Bugzilla: https://bugs.freedesktop.org/106959

Signed-off-by: Mikita Lipski <mikita.lipski at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 42 +++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index ed09e36..c572e86 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -2218,6 +2218,46 @@ get_output_color_space(const struct dc_crtc_timing *dc_crtc_timing)
 	return color_space;
 }
 
+static void reduce_mode_colour_depth(struct dc_crtc_timing *timing_out)
+{
+	if (timing_out->display_color_depth <= COLOR_DEPTH_888)
+		return;
+
+	timing_out->display_color_depth--;
+}
+
+static void check_if_display_depth_is_supported(struct dc_crtc_timing *timing_out,
+						const struct drm_display_info *info)
+{
+	int normalized_clk;
+	if (timing_out->display_color_depth <= COLOR_DEPTH_888)
+		return;
+	do {
+		normalized_clk = timing_out->pix_clk_khz;
+		/* YCbCr 4:2:0 requires additional adjustment of 1/2 */
+		if (timing_out->pixel_encoding == PIXEL_ENCODING_YCBCR420)
+			normalized_clk /= 2;
+		/* Adjusting pix clock following on HDMI spec based on colour depth */
+		switch (timing_out->display_color_depth) {
+		case COLOR_DEPTH_101010:
+			normalized_clk = (normalized_clk * 30) / 24;
+			break;
+		case COLOR_DEPTH_121212:
+			normalized_clk = (normalized_clk * 36) / 24;
+			break;
+		case COLOR_DEPTH_161616:
+			normalized_clk = (normalized_clk * 48) / 24;
+			break;
+		default:
+			return;
+		}
+		if (normalized_clk <= info->max_tmds_clock)
+			return;
+		reduce_mode_colour_depth(timing_out);
+
+	} while (timing_out->display_color_depth > COLOR_DEPTH_888);
+
+}
 /*****************************************************************************/
 
 static void
@@ -2273,6 +2313,8 @@ fill_stream_properties_from_drm_display_mode(struct dc_stream_state *stream,
 
 	stream->out_transfer_func->type = TF_TYPE_PREDEFINED;
 	stream->out_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
+	if (stream->sink->sink_signal == SIGNAL_TYPE_HDMI_TYPE_A)
+		check_if_display_depth_is_supported(timing_out, info);
 }
 
 static void fill_audio_info(struct audio_info *audio_info,
-- 
2.7.4