From: Eric Yang <Eric.Yang2@amd.com>
Date: Fri, 23 Mar 2018 13:56:16 -0400
Subject: drm/amd/display: fix link bw calculation for 422 and 420 encoding
Git-commit: cf65ebeb687678812eb3ddd5ef253bacf7ef330a
Patch-mainline: v4.18-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Link bw required is reduced when we have chroma subsampling.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c |   53 +++++++++++++----------
 1 file changed, 32 insertions(+), 21 deletions(-)

--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -1378,37 +1378,48 @@ static uint32_t bandwidth_in_kbps_from_t
 {
 	uint32_t bits_per_channel = 0;
 	uint32_t kbps;
-	switch (timing->display_color_depth) {
 
-	case COLOR_DEPTH_666:
-		bits_per_channel = 6;
-		break;
-	case COLOR_DEPTH_888:
-		bits_per_channel = 8;
-		break;
-	case COLOR_DEPTH_101010:
-		bits_per_channel = 10;
-		break;
-	case COLOR_DEPTH_121212:
+	if (timing->pixel_encoding == PIXEL_ENCODING_YCBCR422)
 		bits_per_channel = 12;
-		break;
-	case COLOR_DEPTH_141414:
-		bits_per_channel = 14;
-		break;
-	case COLOR_DEPTH_161616:
-		bits_per_channel = 16;
-		break;
-	default:
-		break;
+	else{
+
+		switch (timing->display_color_depth) {
+
+		case COLOR_DEPTH_666:
+			bits_per_channel = 6;
+			break;
+		case COLOR_DEPTH_888:
+			bits_per_channel = 8;
+			break;
+		case COLOR_DEPTH_101010:
+			bits_per_channel = 10;
+			break;
+		case COLOR_DEPTH_121212:
+			bits_per_channel = 12;
+			break;
+		case COLOR_DEPTH_141414:
+			bits_per_channel = 14;
+			break;
+		case COLOR_DEPTH_161616:
+			bits_per_channel = 16;
+			break;
+		default:
+			break;
+		}
 	}
 	ASSERT(bits_per_channel != 0);
 
 	kbps = timing->pix_clk_khz;
 	kbps *= bits_per_channel;
 
-	if (timing->flags.Y_ONLY != 1)
+	if (timing->flags.Y_ONLY != 1) {
 		/*Only YOnly make reduce bandwidth by 1/3 compares to RGB*/
 		kbps *= 3;
+		if (timing->pixel_encoding == PIXEL_ENCODING_YCBCR420)
+			kbps /= 2;
+		else if (timing->pixel_encoding == PIXEL_ENCODING_YCBCR422)
+			kbps = kbps * 2 / 3;
+	}
 
 	return kbps;