Public bug reported:
Impact: Some new laptops with 4k screens are starting to use dp 1.2 only
feature of supporting 5.4ghz link rates over displayport which was not
turned on until 3.15 even though the plumbing for it was (mostly) there.
This should only make more devices work since it has to advertise
support for the feature in the dpcd. previously dp 1.2 screens which
needed 5.4ghz link rates were forced to use 2.7ghz instead, which would
not provide enough bandwidth for some high resolution/high bandwidth
screens. It only affects haswell for trusty, broadwell is handled
through i915_bdw module which already as this fix and the fix was
upstream in 3.15-rc1 so utopic is unaffected.
Fix: Allow the 5.4ghz link rate over displayport.
This has been tested on an affected OEM laptop with a 4K display that
requires 5.4ghz link rate to light up (without it the display never
turns on) as well as 2 other haswell machines to be sure it doesn't
regress.
[ 5.297037] [drm:intel_modeset_stage_output_state] [CONNECTOR:16:eDP-1] to
[CRTC:5]
[ 5.297038] [drm:intel_modeset_affected_pipes] set mode pipe masks: modeset:
1, prepare: 1, disable: 0
[ 5.297040] [drm:connected_sink_compute_bpp] [CONNECTOR:16:eDP-1] checking for
sink bpp constrains
[ 5.297042] [drm:intel_dp_compute_config] DP link computation with max lane
count 4 max bw 14 pixel clock 533250KHz
[ 5.297045] [drm:intel_dp_compute_config] DP link bw 14 lane count 4 clock
540000 bpp 24
[ 5.297046] [drm:intel_dp_compute_config] DP link bw required 1279800
available 1728000
[ 5.297047] [drm:intel_modeset_pipe_config] plane bpp: 24, pipe bpp: 24,
dithering: 0
** Affects: hwe-next
Importance: Undecided
Status: New
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1369633
Title:
4k laptop eDP display not working on a dell precision m3800
Status in HWE Next Project:
New
Status in “linux” package in Ubuntu:
New
Bug description:
Impact: Some new laptops with 4k screens are starting to use dp 1.2
only feature of supporting 5.4ghz link rates over displayport which
was not turned on until 3.15 even though the plumbing for it was
(mostly) there. This should only make more devices work since it has
to advertise support for the feature in the dpcd. previously dp 1.2
screens which needed 5.4ghz link rates were forced to use 2.7ghz
instead, which would not provide enough bandwidth for some high
resolution/high bandwidth screens. It only affects haswell for trusty,
broadwell is handled through i915_bdw module which already as this fix
and the fix was upstream in 3.15-rc1 so utopic is unaffected.
Fix: Allow the 5.4ghz link rate over displayport.
This has been tested on an affected OEM laptop with a 4K display that
requires 5.4ghz link rate to light up (without it the display never
turns on) as well as 2 other haswell machines to be sure it doesn't
regress.
[ 5.297037] [drm:intel_modeset_stage_output_state] [CONNECTOR:16:eDP-1] to
[CRTC:5]
[ 5.297038] [drm:intel_modeset_affected_pipes] set mode pipe masks: modeset:
1, prepare: 1, disable: 0
[ 5.297040] [drm:connected_sink_compute_bpp] [CONNECTOR:16:eDP-1] checking
for sink bpp constrains
[ 5.297042] [drm:intel_dp_compute_config] DP link computation with max lane
count 4 max bw 14 pixel clock 533250KHz
[ 5.297045] [drm:intel_dp_compute_config] DP link bw 14 lane count 4 clock
540000 bpp 24
[ 5.297046] [drm:intel_dp_compute_config] DP link bw required 1279800
available 1728000
[ 5.297047] [drm:intel_modeset_pipe_config] plane bpp: 24, pipe bpp: 24,
dithering: 0
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