Bug 206157

Summary: Apple MacBookPro 2017 Retina panel doesn't reach 10 bit native precision due to low eDP link settings.
Product: Drivers Reporter: Mario Kleiner (mario.kleiner)
Component: Video(Other)Assignee: drivers_video-other
Status: RESOLVED INVALID    
Severity: normal    
Priority: P1    
Hardware: Intel   
OS: Linux   
Kernel Version: 5.5-rc Subsystem:
Regression: No Bisected commit-id:
Attachments: DPCD dump of the first ~5000 Bytes/Regs

Description Mario Kleiner 2020-01-10 15:46:13 UTC
Created attachment 286741 [details]
DPCD dump of the first ~5000 Bytes/Regs

The panel reports 10 bpc color depth in its EDID, and the UEFI
firmware chooses link settings at boot which support enough
bandwidth for 10 bpc (324000 kbit/sec to be precise, aka DP_LINK_BW_SET == 0xc), but the DP_MAX_LINK_RATE dpcd register only reports 0xa == 2.7 Gbps as possible,
so intel_dp_set_sink_rates() would cap at that. This restricts
achievable color depth to 8 bpc, not providing the full color
depth of the panel.

This report relates to dri-devel patch "drm/i915/dp: Add current maximum eDP link rate to sink_rate array."

Attached is a DPCD dump of the first ~ 5000 Bytes/Registers of the eDP panel.
Comment 1 Jani Nikula 2020-01-17 09:54:26 UTC
FWIW we don't really look at i915 bugs at bugzilla.kernel.org, except to tell you to report i915 bugs at https://gitlab.freedesktop.org/drm/intel/issues/new