[SRU] [G/H/Unstable/OEM-5.10] [PATCH 0/2] Fix screen flickering on some panels

[Kai-Heng Feng]

BugLink: https://bugs.launchpad.net/bugs/1925685

[Impact]
We are having screen flickering and glitching issues with some of our
hardware upon wake from suspend. We have worked with our ODM to figure
out a fix for this. They had reported there were no issues when running
Windows on the same hardware. As such, we tested, and found that this
issue first began as a regression in kernel 5.0 (did not exist in kernel
4.18 per our tests).

We identified a patch via
https://gitlab.freedesktop.org/drm/intel/-/issues/272 in which this has
been solved. Per our testing by recompiling the kernel, this completely
fixes our hardware issue. As of 4-21, this fix has been merged into the
Linux kernel per Timo Aaltonen, and will be included in the kernel in
the 5.13 release.

Our hardware ships with Kubuntu 20.04 LTS, which means the 5.13 kernel
will not see these machines, at least in the forseeable future. As such,
we request that this patch be added to the kernel. Per our testing, this
patch is straightforward to add and works flawlessly.

The patch that works best was created in collaboration with Kai-Heng
Feng, is attached to this bug report, and can be found here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1925685/+attachment/5491421/+files/drm-intel-both.patch

Until this is fixed, we have a whole batch of hardware we cannot sell,
so, as an OEM, this is a high priority.

[Test Plan]
* Install Kubuntu on an affected Kubuntu Focus M2 computer (not in the
  hands of customers at this time)

* Notice screen glitching/flickering after wake-from-suspend.

* Install kernel compiled with the attached patch. Boot from patched
  kernel.

* Suspend laptop, resume. No glitches.

[Where problems could occur]
Although this solves the problem for us and has been confirmed to
work with the Intel developers that developed this patch, it could
cause another display type to have problems. This is unlikely as it
has been vetted by Intel and by the mainline Linux kernel
developers.

Kai-Heng Feng (1):
  UBUNTU: SAUCE: drm/i915/dp: Use slow and wide link training for
    everything

Ville Syrjälä (1):
  drm/i915: Try to use fast+narrow link on eDP again and fall back to
    the old max strategy on failure

 .../drm/i915/display/intel_display_types.h    |  1 +
 drivers/gpu/drm/i915/display/intel_dp.c       | 21 +++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

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