[PATCH 20/34] drm/amd/display: When enabling CRC, disable dither & enable truncation

[Harry Wentland]

From: "Leo (Sunpeng) Li" <sunpeng.li at amd.com>

When user-mode is using 8bpc, the hardware represents it internally
using a higher bit depth. This causes problems when comparing CRCs for
color managment tests.

We need to disable dithering as well, since it makes CRC values
non-deterministic.

It's easy to see why dithering needs to be disabled, The reason why
truncation also needs to be enabled is better described with an example.
Consider the folowing which tests the color transform matrix (CTM):

Expected CRC = FB_A -> Degamma (Bypassed) -> CTM (Bypassed)
                                                  |
                                                  v
                            Obtain CRC  <- Regamma(Bypassed)

Actual CRC = FB_B -> Degamma (Bypassed) -> CTM (0.5*Identity)
                                                  |
                                                  v
                            Obtain CRC  <- Regamma(Bypassed)

FB_A contains a solid red color at half intensity (127 @ 8bpc)
FB_B contains a solid red color at full intensity (255 @ 8bpc)

We expect that Expected CRC = Actual CRC, but that's not the case. When
the CTM is applied, the output is at half intensity, but also at a
higher bit depth within hardware. i.e. 255/2 = 127.5: not representable
in 8bpc, but can be at 10bpc. This causes the two CRC's to be different.

The solution is to truncate the output bit depth to the same as input
when enabling CRC capture. Since Linux only supports 8bpc, hard code
that for now.

Change-Id: Ic9277659ec785d655989ba0c6d170b1691525376
Signed-off-by: Leo (Sunpeng) Li <sunpeng.li at amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c | 11 +++++++++--
 drivers/gpu/drm/amd/display/dc/core/dc.c              | 14 +++++++++++---
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c
index e5fb53a56b73..55aa379cfcbe 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c
@@ -60,18 +60,25 @@ int amdgpu_dm_crtc_set_crc_source(struct drm_crtc *crtc, const char *src_name,
 		return -EINVAL;
 	}
 
+	/* When enabling CRC, we should also disable dithering. */
 	if (source == AMDGPU_DM_PIPE_CRC_SOURCE_AUTO) {
 		if (dc_stream_configure_crc(stream_state->ctx->dc,
 					    stream_state,
-					    true, true))
+					    true, true)) {
 			crtc_state->crc_enabled = true;
+			dc_stream_set_dither_option(stream_state,
+						    DITHER_OPTION_TRUN8);
+		}
 		else
 			return -EINVAL;
 	} else {
 		if (dc_stream_configure_crc(stream_state->ctx->dc,
 					    stream_state,
-					    false, false))
+					    false, false)) {
 			crtc_state->crc_enabled = false;
+			dc_stream_set_dither_option(stream_state,
+						    DITHER_OPTION_DEFAULT);
+		}
 		else
 			return -EINVAL;
 	}
diff --git a/drivers/gpu/drm/amd/display/dc/core/dc.c b/drivers/gpu/drm/amd/display/dc/core/dc.c
index ea5c35166ffa..f4ffbf2e2caf 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc.c
@@ -316,7 +316,6 @@ void dc_stream_set_dither_option(struct dc_stream_state *stream,
 		}
 	}
 
-	memset(&params, 0, sizeof(params));
 	if (!pipes)
 		return;
 	if (option > DITHER_OPTION_MAX)
@@ -324,9 +323,18 @@ void dc_stream_set_dither_option(struct dc_stream_state *stream,
 
 	stream->dither_option = option;
 
-	resource_build_bit_depth_reduction_params(stream,
-				&params);
+	memset(&params, 0, sizeof(params));
+	resource_build_bit_depth_reduction_params(stream, &params);
 	stream->bit_depth_params = params;
+
+	if (pipes->plane_res.xfm &&
+	    pipes->plane_res.xfm->funcs->transform_set_pixel_storage_depth) {
+		pipes->plane_res.xfm->funcs->transform_set_pixel_storage_depth(
+			pipes->plane_res.xfm,
+			pipes->plane_res.scl_data.lb_params.depth,
+			&stream->bit_depth_params);
+	}
+
 	pipes->stream_res.opp->funcs->
 		opp_program_bit_depth_reduction(pipes->stream_res.opp, &params);
 }
-- 
2.14.1