[PATCH 0/1][SRU][Focal] Intermittent display blackouts on event

AceLan Kao acelan.kao at canonical.com
Wed Apr 29 02:55:27 UTC 2020

BugLink: https://bugs.launchpad.net/bugs/1875254

When audio device enters runpm D3(idle for 7 seconds) and then wakes it up
to make a sound, it flicks the screen.
This behavior could be observed while plug/remove AC cable or USB disk,
or open a terminal and press backsapce key.

This issue could be fixed by this commit, it fixes the flicker during
boot-time, but it also fixes the flicker during rumtime wakeup.
1ee48a61aa57 drm/i915: Limit audio CDCLK>=2*BCLK constraint back to GLK only

Audio drivers communicate with i915 over HDA bus multiple times during
system boot-up and each of these transactions result in matching
get_power/put_power calls to i915, and depending on the platform,
a modeset change causing visible flicker.

GLK is the only platform with minimum CDCLK significantly lower
than BCLK, and thus for GLK setting a higher CDCLK is mandatory.

For other platforms, minimum CDCLK is close but below 2*BCLK
(e.g. on ICL, CDCLK=176.4kHz with BCLK=96kHz). Spec-wise the constraint
should be set, but in practise no communication errors have been
reported and the downside if set is the flicker observed at boot-time.

Verified on Dell XPS 13 9300

[Regression Potential]
Low, it fixes below commit which contains in ubuntu kernel and should have
been applied on ubuntu kernel, too.
Fixes: f6ec9483091f ("drm/i915: extend audio CDCLK>=2*BCLK constraint to more platforms")

Kai Vehmanen (1):
  drm/i915: Limit audio CDCLK>=2*BCLK constraint back to GLK only

 drivers/gpu/drm/i915/display/intel_audio.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)


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