[PATCH 0/1][SRU][D/E] UBUNTU: SAUCE: drm/i915: Disable PSR by default on all platforms

[Sultan Alsawaf]

BugLink: https://bugs.launchpad.net/bugs/1849947

In Linux 5.0, PSR (Panel Self Refresh) was enabled by default on capable
hardware using Intel integrated graphics. On the few consumer laptops that do
have a panel with PSR support, enabling PSR causes frequent graphical glitches
that severely impact user experience. Dell laptops are the primary example; it
appears that no Thinkpads come with panels that support PSR, and it's unknown
how many other OEMs ship laptops with PSR, so let's just play it safe and
assume that PSR doesn't work for anyone.

[Impact]
PSR is an esoteric power-saving mechanism that will not be dearly missed when
disabled. The accompanying patch simply toggles PSR off by default in i915; it
can be re-enabled by the end user at the expense of tainting their kernel. The
power savings from enabling PSR are slim enough that I didn't observe a
difference in my laptop's reported power consumption between when I had it
enabled and disabled.

[Fix]
Set the enable_psr parameter in the i915 driver to 0 by default.

[Test Case]
I booted up a patched kernel on a laptop with PSR support and the debugfs node
that reports the status of PSR (/sys/kernel/debug/dri/0/i915_edp_psr_status)
said it was disabled. The graphical glitches were also gone.

[Regression Risk]
Low. This just restores the pre-5.0 behavior of keeping PSR disabled by default
on capable hardware.

Sultan Alsawaf (1):
  UBUNTU: SAUCE: drm/i915: Disable PSR by default on all platforms

 drivers/gpu/drm/i915/i915_params.c | 3 +--
 drivers/gpu/drm/i915/i915_params.h | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

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2.20.1