[SRU][H/Unstable][PATCH 0/2] Display abnormal on the TGL+4k panel machines

[Hui Wang]

BugLink: https://bugs.launchpad.net/bugs/1922885

The same patches were sent to oem-5.10 for a while, the OEM project
worked well with these 2 patches. When I sent the patches to oem-5.10,
I thought the patches are temporary workaround from Intel, they will
replace them with a real fix. But by now, Intel still uses the patches
to fix this issue, looks like they are the real fix. So I send them to
generic kernel of H and Unstable.


[Impact]
On the TGL machines, if the panel is 4k resolution and the i915 driver
is in PSR2 mode, the display will be abnormal randomly and the
keyboard reponse is delayed randomly.

[Fix]
We reported this issue to Intel and Lenovo shipped a machine to Intel
developer, they reproduced the issue and they provided a workaroud
patch.

[Test]
Booting the system with patched kernel, open 10+ terminal windows,
move those windows or resize those windows for 10 mins, the display
is good. Open a terminal and press 1, 2, 3 and 4 keys rapidly and
repeatedly, the 1, 2, 3, 4 is showed on the terminal immediately,
there is no delay between pressing and showing.


[Where problems could occur]
After applying these patches, the DC3 clock off mode is disabled
unconditionally on the TGL+PSR2 machines, this could introduce
power consumption regression. But we tested the patched kernel on
different TGL lenovo machines, all power_management test cases passed.

Gwan-gyeong Mun (2):
  drm/i915/display: Do not allow DC3CO if PSR SF is enabled
  UBUNTU: SAUCE: drm/i915/display/psr: Disable DC3CO when the PSR2 is
    used

 drivers/gpu/drm/i915/display/intel_psr.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

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2.25.1