accel: ethosu: Remove redundant job_lock

The job_lock mutex guarded dev->in_flight_job across ethosu_job_run(),
the threaded IRQ handler, and ethosu_job_timedout(). However, the DRM
scheduler already provides most of the serialization required, which
makes this mutex redundant.

Analyzing the different scenarios:

  1. run_job() and timedout_job() are mutually exclusive scheduler
     callbacks, so the scheduler itself serializes them.

  2. run_job() and the IRQ handler are implicitly serialized, but they can
     overlap in time: dma_fence_signal() synchronously queues the next
     run_job onto submit_wq, and the worker can execute run_job(next) on
     another CPU before the IRQ thread finishes. The mutex previously kept
     the IRQ's trailing "in_flight_job = NULL" from racing run_job(next)'s
     "in_flight_job = next" store.

     The handler is now restructured to clear in_flight_job before calling
     dma_fence_signal(), so any run_job(next) woken by the signal observes
     NULL.

  3. timedout_job() and the IRQ handler can also overlap if the hardware
     completes the timed-out job near the timeout boundary, since
     drm_sched_stop()'s cancel_work_sync() only synchronizes with the
     scheduler's workqueue. The IRQ handler saves in_flight_job into a
     local with READ_ONCE() before dereferencing ->done_fence, and
     run_job()/timedout_job() publish the field with WRITE_ONCE(). This
     prevents the compiler from reloading the pointer, and keeps the IRQ
     thread operating on the same job for the duration of the handler even
     if timedout_job() concurrently clears the field.

Drop the mutex along with its initialization.

Signed-off-by: Maíra Canal <mcanal@igalia.com>
Link: https://patch.msgid.link/20260516144623.2582427-2-mcanal@igalia.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

0 files changed, 0 insertions, 0 deletions