[SRU][J][PATCH 0/1] drm/i915: Skip some timing checks on BXT/GLK DSI transcoders

[Dariusz Gadomski]

BugLink: https://bugs.launchpad.net/bugs/2044131

[ Impact ]
Commit 8f4b1068e7fc3df1a77ac8151767e56b208cc87f introduced some timing checks
which have been proven invalid for at least some hardware setups.  A user trying
to run Focal with HWE 5.15 kernel is not able to get any video output.  After
going through bisection between 5.4 and 5.5 this commit was identified.
Reverting it on top of Focal HWE kernel fixes the issue.

The issue has also been addressed upstream in DRM tree
(20c2dbff342aec13bf93c2f6c951da198916a455) and has been merge into linux-next
(e0ef2daa8ca8ce4dbc2fd0959e383b753a87fd7d).

dmesg and lspci from the affected configuration are attached to this bug.

[ Test Plan ]
1. Boot the affected hardware with Ubuntu desktop running kernel v5.5 or higher.
2. Wait until boot finishes and see the blank screen.

Actual result: there is no video output visible.  Expected result: normal boot
process should be visible (e.g. splash), then GUI should appear.

[ Where problem could occur ]
This bug was a result of assumptions in the checks that turned out to be not
valid for some hardware. The checks were removed from global intel_mode_valid
function and moved into connector specific .mode_valid() hooks, entirely skiping
BXT/GLK DSI connectors.

This should keep the checks where appropriate and skip for hardware that does
not comply to them.

Ville Syrjälä (1):
  drm/i915: Skip some timing checks on BXT/GLK DSI transcoders

 drivers/gpu/drm/i915/display/icl_dsi.c       |  7 +++++++
 drivers/gpu/drm/i915/display/intel_crt.c     |  5 +++++
 drivers/gpu/drm/i915/display/intel_display.c | 10 ++++++++++
 drivers/gpu/drm/i915/display/intel_display.h |  3 +++
 drivers/gpu/drm/i915/display/intel_dp.c      |  4 ++++
 drivers/gpu/drm/i915/display/intel_dp_mst.c  |  4 ++++
 drivers/gpu/drm/i915/display/intel_dvo.c     | 16 +++++++++++-----
 drivers/gpu/drm/i915/display/intel_hdmi.c    |  4 ++++
 drivers/gpu/drm/i915/display/intel_lvds.c    |  8 +++++++-
 drivers/gpu/drm/i915/display/intel_sdvo.c    |  8 +++++++-
 drivers/gpu/drm/i915/display/intel_tv.c      |  8 +++++++-
 drivers/gpu/drm/i915/display/vlv_dsi.c       | 18 +++++++++++++++++-
 12 files changed, 86 insertions(+), 9 deletions(-)

-- 
2.34.1