From 512fb759ffaf58354ec8b967b9d9df917dd609a8 Mon Sep 17 00:00:00 2001
From: Aun-Ali Zaidi <admin@kodeit.net>
Date: Sat, 29 Jan 2022 05:49:55 +0000
Subject: drm/amd/display: Force link_rate as LINK_RATE_RBR2 for 2018 15" Apple
 Retina panels
Git-commit: 30fbce374745a9c6af93c775a5ac49a97f822fda
Patch-mainline: v5.17-rc3
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225

The eDP link rate reported by the DP_MAX_LINK_RATE dpcd register (0xa) is
contradictory to the highest rate supported reported by
EDID (0xc = LINK_RATE_RBR2). The effects of this compounded with commit
'4a8ca46bae8a ("drm/amd/display: Default max bpc to 16 for eDP")' results
in no display modes being found and a dark panel.

For now, simply force the maximum supported link rate for the eDP attached
2018 15" Apple Retina panels.

Additionally, we must also check the firmware revision since the device ID
reported by the DPCD is identical to that of the more capable 16,1,
incorrectly quirking it. We also use said firmware check to quirk the
refreshed 15,1 models with Vega graphics as they use a slightly newer
firmware version.

Tested-by: Aun-Ali Zaidi <admin@kodeit.net>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Aun-Ali Zaidi <admin@kodeit.net>
Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 .../gpu/drm/amd/display/dc/core/dc_link_dp.c  | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

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 4c3ab2575e4b..61b8f29a0c30 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
@@ -5597,6 +5597,26 @@ static bool retrieve_link_cap(struct dc_link *link)
 		dp_hw_fw_revision.ieee_fw_rev,
 		sizeof(dp_hw_fw_revision.ieee_fw_rev));
 
+	/* Quirk for Apple MBP 2018 15" Retina panels: wrong DP_MAX_LINK_RATE */
+	{
+		uint8_t str_mbp_2018[] = { 101, 68, 21, 103, 98, 97 };
+		uint8_t fwrev_mbp_2018[] = { 7, 4 };
+		uint8_t fwrev_mbp_2018_vega[] = { 8, 4 };
+
+		/* We also check for the firmware revision as 16,1 models have an
+		 * identical device id and are incorrectly quirked otherwise.
+		 */
+		if ((link->dpcd_caps.sink_dev_id == 0x0010fa) &&
+		    !memcmp(link->dpcd_caps.sink_dev_id_str, str_mbp_2018,
+			     sizeof(str_mbp_2018)) &&
+		    (!memcmp(link->dpcd_caps.sink_fw_revision, fwrev_mbp_2018,
+			     sizeof(fwrev_mbp_2018)) ||
+		    !memcmp(link->dpcd_caps.sink_fw_revision, fwrev_mbp_2018_vega,
+			     sizeof(fwrev_mbp_2018_vega)))) {
+			link->reported_link_cap.link_rate = LINK_RATE_RBR2;
+		}
+	}
+
 	memset(&link->dpcd_caps.dsc_caps, '\0',
 			sizeof(link->dpcd_caps.dsc_caps));
 	memset(&link->dpcd_caps.fec_cap, '\0', sizeof(link->dpcd_caps.fec_cap));
-- 
2.38.1