From: "Leo (Sunpeng) Li" <sunpeng.li@amd.com>
Date: Tue, 6 Feb 2018 10:20:46 -0500
Subject: drm/amd/display: Skip 2 frames when first reading CRC
Git-commit: a0a31ec4ce6a8c8bc4f4b8619b537e4a9a0ddaf1
Patch-mainline: v4.17-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Skipping the first frame will prevent uncoooked values most of the time.
However, in some unlikely cases, the second frame will be uncooked as
well.

Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-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/amdgpu_dm/amdgpu_dm.h     |    2 +-
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c |   12 ++++++------
 2 files changed, 7 insertions(+), 7 deletions(-)

--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
@@ -198,7 +198,7 @@ struct dm_crtc_state {
 	struct drm_crtc_state base;
 	struct dc_stream_state *stream;
 
-	bool crc_first_skipped;
+	int crc_skip_count;
 	bool crc_enabled;
 };
 
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crc.c
@@ -84,8 +84,8 @@ int amdgpu_dm_crtc_set_crc_source(struct
 	}
 
 	*values_cnt = 3;
-	/* Reset crc_skipped flag on dm state */
-	crtc_state->crc_first_skipped = false;
+	/* Reset crc_skipped on dm state */
+	crtc_state->crc_skip_count = 0;
 	return 0;
 }
 
@@ -109,11 +109,11 @@ void amdgpu_dm_crtc_handle_crc_irq(struc
 	/*
 	 * Since flipping and crc enablement happen asynchronously, we - more
 	 * often than not - will be returning an 'uncooked' crc on first frame.
-	 * Probably because hw isn't ready yet. Simply skip the first crc
-	 * value.
+	 * Probably because hw isn't ready yet. For added security, skip the
+	 * first two CRC values.
 	 */
-	if (!crtc_state->crc_first_skipped) {
-		crtc_state->crc_first_skipped = true;
+	if (crtc_state->crc_skip_count < 2) {
+		crtc_state->crc_skip_count += 1;
 		return;
 	}