[PATCH 0/1][SRU][L/M/U] Fix eDP only displays 3/4 area after switching to mirror mode with external HDMI 4K monitor

[Chris Chiu]

BugLink: https://bugs.launchpad.net/bugs/2024273

[Impact]
Panel on laptops connect to some 4K monitors via HDMI only display 3/4 area on eDP after switching to mirror mode.

[Fix]
Backport a fix from Intel on https://cgit.freedesktop.org/drm-tip/commit/?id=a2da67028cd05516343533c1609fcaf037237fed.

[Test]
1. Power on the laptop
2. Connect a 4K monitor (4k Benq EL2870U, 4k HP z27Kg3, 2k ASUS PA27AC) to the laptop with HDMI cable.
3. Switch to mirror mode from default Joint Mode
4. Verify there's no obvious blank space on the leftmost/rightmost side of the laptop's panel.

[Where problems could occur]
Only observed after connecting with some particular 4K monitors. It's a generic fix to accept arbitrary refresh rate for more advanced panels. Should be low risk to old machines.

Ville Syrjälä (1):
  drm/i915: Allow arbitrary refresh rates with VRR eDP panels

 drivers/gpu/drm/i915/display/intel_panel.c | 80 ++++++++++++++++++----
 1 file changed, 66 insertions(+), 14 deletions(-)

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2.25.1