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[v2,0/5] i915: dedicated MCR locking and hardware semaphore

Message ID 20221128233014.4000136-1-matthew.d.roper@intel.com (mailing list archive)
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Series i915: dedicated MCR locking and hardware semaphore | expand

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Matt Roper Nov. 28, 2022, 11:30 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.

v2:
 - Use irqsave/irqrestore locking; on platforms that use execlist
   submission instead of GuC, MCR accesses can happen in interrupt
   context (tasklet) during reset -> error dump.
 - Extend timeout for hardware semaphore and CI taint if we ever
   encounter it (this implies a hardware/firmware problem).  (Mika)
 - Add an extra patch optimizing xehp_setup_private_ppat by holding
   forcewake & mcr lock over the sequence of register writes.  (Bala)

Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>

Matt Roper (5):
  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
  drm/i915/mtl: Hold forcewake and MCR lock over PPAT setup

 drivers/gpu/drm/i915/gt/intel_gt.c          |   7 +-
 drivers/gpu/drm/i915/gt/intel_gt_mcr.c      | 129 ++++++++++++++++++--
 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_gtt.c         |  27 ++--
 drivers/gpu/drm/i915/gt/intel_mocs.c        |   3 +
 drivers/gpu/drm/i915/gt/intel_workarounds.c |  12 +-
 8 files changed, 162 insertions(+), 27 deletions(-)