linux-kernel - [PATCH 5.2 055/215] drm/amd/display: Update link rate from DPCD 10

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Date:   Mon, 29 Jul 2019 21:20:51 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Wesley Chalmers <Wesley.Chalmers@....com>,
        Anthony Koo <Anthony.Koo@....com>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.2 055/215] drm/amd/display: Update link rate from DPCD 10

[ Upstream commit 53c81fc7875bc2dca358485dac3999e14ec91a00 ]

[WHY]
Some panels return a link rate of 0 (unknown) in DPCD 0. In this case,
an appropriate mode cannot be set, and certain panels will show
corruption as they are forced to use a mode they do not support.

[HOW]
Read DPCD 10 in the case where supported link rate from DPCD 0 is
unknown, and pass that value on to the reported link rate.
This re-introduces behaviour present in previous versions that appears
to have been accidentally removed.

Signed-off-by: Wesley Chalmers <Wesley.Chalmers@....com>
Reviewed-by: Anthony Koo <Anthony.Koo@....com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
index 1ee544a32ebb..253311864cdd 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c
@@ -1624,8 +1624,7 @@ static bool decide_edp_link_settings(struct dc_link *link, struct dc_link_settin
 	uint32_t link_bw;
 
 	if (link->dpcd_caps.dpcd_rev.raw < DPCD_REV_14 ||
-			link->dpcd_caps.edp_supported_link_rates_count == 0 ||
-			link->dc->config.optimize_edp_link_rate == false) {
+			link->dpcd_caps.edp_supported_link_rates_count == 0) {
 		*link_setting = link->verified_link_cap;
 		return true;
 	}
@@ -2597,7 +2596,8 @@ void detect_edp_sink_caps(struct dc_link *link)
 	memset(supported_link_rates, 0, sizeof(supported_link_rates));
 
 	if (link->dpcd_caps.dpcd_rev.raw >= DPCD_REV_14 &&
-			link->dc->config.optimize_edp_link_rate) {
+			(link->dc->config.optimize_edp_link_rate ||
+			link->reported_link_cap.link_rate == LINK_RATE_UNKNOWN)) {
 		// Read DPCD 00010h - 0001Fh 16 bytes at one shot
 		core_link_read_dpcd(link, DP_SUPPORTED_LINK_RATES,
 							supported_link_rates, sizeof(supported_link_rates));
@@ -2612,6 +2612,9 @@ void detect_edp_sink_caps(struct dc_link *link)
 				link_rate = linkRateInKHzToLinkRateMultiplier(link_rate_in_khz);
 				link->dpcd_caps.edp_supported_link_rates[link->dpcd_caps.edp_supported_link_rates_count] = link_rate;
 				link->dpcd_caps.edp_supported_link_rates_count++;
+
+				if (link->reported_link_cap.link_rate < link_rate)
+					link->reported_link_cap.link_rate = link_rate;
 			}
 		}
 	}
-- 
2.20.1