This fixes a problem found on the MacBookPro 2017 Retina panel:
The panel reports 10 bpc color depth in its EDID, and the
firmware chooses link settings at boot which support enough
bandwidth for 10 bpc (324000 kbit/sec aka LINK_RATE_RBR2
aka 0xc), but the DP_MAX_LINK_RATE dpcd register only reports
2.7 Gbps (multiplier value 0xa) as possible, in direct
contradiction of what the firmware successfully set up.
This restricts the panel to 8 bpc, not providing the full
color depth of the panel on Linux <= 5.5. Additionally, commit
'4a8ca46bae8a ("drm/amd/display: Default max bpc to 16 for eDP")'
introduced into Linux 5.6-rc1 will unclamp panel depth to
its full 10 bpc, thereby requiring a eDP bandwidth for all
modes that exceeds the bandwidth available and causes all modes
to fail validation -> No modes for the laptop panel -> failure
to set any mode -> Panel goes dark.
This patch adds a quirk specific to the MBP 2017 15" Retina
panel to override reported max link rate to the correct maximum
of 0xc = LINK_RATE_RBR2 to fix the darkness and reduced display
precision.
Please apply for Linux 5.6+ to avoid regressing Apple MBP panel
support.
Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx>
---
drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c | 11 +++++++++++
1 file changed, 11 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 cb731c1d30b1..fd9e69634c50 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
@@ -3401,6 +3401,17 @@ static bool retrieve_link_cap(struct dc_link *link)
sink_id.ieee_device_id,
sizeof(sink_id.ieee_device_id));
+ /* Quirk Apple MBP 2017 15" Retina panel: Wrong DP_MAX_LINK_RATE */
+ {
+ uint8_t str_mbp_2017[] = { 101, 68, 21, 101, 98, 97 };
+
+ if ((link->dpcd_caps.sink_dev_id == 0x0010fa) &&
+ !memcmp(link->dpcd_caps.sink_dev_id_str, str_mbp_2017,
+ sizeof(str_mbp_2017))) {
+ link->reported_link_cap.link_rate = 0x0c;
+ }
+ }
+
core_link_read_dpcd(
link,
DP_SINK_HW_REVISION_START,
--
2.20.1
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