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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Harry Wentland <harry.wentland@amd.com>,
        Werner Sembach <wse@tuxedocomputers.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.10 194/299] drm/amd/display: Try YCbCr420 color when YCbCr444 fails
Date:   Mon, 10 May 2021 12:19:51 +0200
Message-Id: <20210510102011.355656279@linuxfoundation.org>
In-Reply-To: <20210510102004.821838356@linuxfoundation.org>
References: <20210510102004.821838356@linuxfoundation.org>
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From: Werner Sembach <wse@tuxedocomputers.com>

[ Upstream commit 68eb3ae3c63708f823aeeb63bb15197c727bd9bf ]

When encoder validation of a display mode fails, retry with less bandwidth
heavy YCbCr420 color mode, if available. This enables some HDMI 1.4 setups
to support 4k60Hz output, which previously failed silently.

On some setups, while the monitor and the gpu support display modes with
pixel clocks of up to 600MHz, the link encoder might not. This prevents
YCbCr444 and RGB encoding for 4k60Hz, but YCbCr420 encoding might still be
possible. However, which color mode is used is decided before the link
encoder capabilities are checked. This patch fixes the problem by retrying
to find a display mode with YCbCr420 enforced and using it, if it is
valid.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 9 +++++++++
 1 file changed, 9 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 12a4f0675fb0..d18341b7daac 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -5328,6 +5328,15 @@ create_validate_stream_for_sink(struct amdgpu_dm_connector *aconnector,
 
 	} while (stream == NULL && requested_bpc >= 6);
 
+	if (dc_result == DC_FAIL_ENC_VALIDATE && !aconnector->force_yuv420_output) {
+		DRM_DEBUG_KMS("Retry forcing YCbCr420 encoding\n");
+
+		aconnector->force_yuv420_output = true;
+		stream = create_validate_stream_for_sink(aconnector, drm_mode,
+						dm_state, old_stream);
+		aconnector->force_yuv420_output = false;
+	}
+
 	return stream;
 }
 
-- 
2.30.2