[0/4] i915: dedicated MCR locking and hardware semaphore

Message

Matt Roper Nov. 22, 2022, 8:33 p.m. UTC

We've been overloading uncore->lock to protect access to the MCR
steering register.  That's not really what uncore->lock is intended for,
and it would be better if we didn't need to hold such a high-traffic
spinlock for the whole sequence of (apply steering, access MCR register,
restore steering).  Switch to a dedicated MCR lock to protect the
steering control register over this critical section and stop relying on
the high-traffic uncore->lock.  On pre-MTL platforms the dedicated MCR
lock is just another software lock, but on MTL and beyond we also
utilize the hardware-provided STEER_SEMAPHORE that allows us to
synchronize with external hardware and firmware agents.

Matt Roper (4):
  drm/i915/gt: Correct kerneldoc for intel_gt_mcr_wait_for_reg()
  drm/i915/gt: Pass gt rather than uncore to lowest-level reads/writes
  drm/i915/gt: Add dedicated MCR lock
  drm/i915/mtl: Add hardware-level lock for steering

 drivers/gpu/drm/i915/gt/intel_gt.c          |   2 +
 drivers/gpu/drm/i915/gt/intel_gt_mcr.c      | 107 ++++++++++++++++++--
 drivers/gpu/drm/i915/gt/intel_gt_mcr.h      |   2 +
 drivers/gpu/drm/i915/gt/intel_gt_regs.h     |   1 +
 drivers/gpu/drm/i915/gt/intel_gt_types.h    |   8 ++
 drivers/gpu/drm/i915/gt/intel_mocs.c        |   2 +
 drivers/gpu/drm/i915/gt/intel_workarounds.c |   4 +
 7 files changed, 115 insertions(+), 11 deletions(-)