[PATCH v2 0/7] drm/i915/display: Handle vblank evasion with CONFIG_PREEMPT_RT

[Maarten Lankhorst <dev@lankhorst.se>]

There is a critical section between intel_pipe_update_start() and
intel_pipe_update_end() where we only program hardware registers,
should not take any lock and complete as fast as possible.

The previous approach used to remove the local_irq_enable/disable()
in this critical, but that increases the probability that the time
sensitive section does not complete in 100 µs, potentially causing
the hardware to hang.

I went through all the lockdep splats that occurred in CI, and fixed
them 1 by 1 until there were none left. This additionally improves
latency by not removing any locks in the fastpath.

In intel_de.h the implicit DMC wakelock was added, ideally we can get rid
of it, but for now we can simply use the same _fw variants as are
needed on i915.

I believe this series is enough to make xe and perhaps good enough to make
i915's display RT safe.

Changes since v1:
- Fix compilation on i915.
- Submit to intel-gfx ml too.s

Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Clark Williams <clrkwllms@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>

Maarten Lankhorst (6):
  drm/i915/display: Make get_vblank_counter use intel_de_read_fw()
  drm/i915/display: Use intel_de_write_fw in intel_pipe_fastset
  drm/i915/display: Move vblank put until after critical section
  drm/i915/display: Remove locking from intel_vblank_evade critical
    section
  drm/i915/display: Make icl_dsi_frame_update use _fw too
  drm/i915/display: Enable interrupts earlier on PREEMPT_RT

Mike Galbraith (1):
  drm/i915: Use preempt_disable/enable_rt() where recommended

 drivers/gpu/drm/i915/display/icl_dsi.c        |  4 +-
 drivers/gpu/drm/i915/display/intel_crtc.c     | 10 +++
 drivers/gpu/drm/i915/display/intel_cursor.c   |  8 +-
 drivers/gpu/drm/i915/display/intel_de.h       |  6 ++
 drivers/gpu/drm/i915/display/intel_display.c  | 36 ++++-----
 drivers/gpu/drm/i915/display/intel_vblank.c   | 80 ++++++++++++-------
 drivers/gpu/drm/i915/display/intel_vrr.c      | 16 ++--
 .../drm/xe/compat-i915-headers/intel_uncore.h |  2 +
 8 files changed, 103 insertions(+), 59 deletions(-)

-- 
2.51.0