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accel: ethosu: Remove redundant job_lock

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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>
This commit is contained in:
Maíra Canal
2026-05-16 11:40:59 -03:00
committed by Rob Herring (Arm)
parent 640c57d6ca
commit 2e5268fc45
2 changed files with 8 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/accel/ethosu/ethosu_device.h
View File

@@ -195,8 +195,6 @@ struct ethosu_device {
struct drm_ethosu_npu_info npu_info;
struct ethosu_job *in_flight_job;
/* For in_flight_job and ethosu_job_hw_submit() */
struct mutex job_lock;
/* For dma_fence */
spinlock_t fence_lock;

22
drivers/accel/ethosu/ethosu_job.c
View File

@@ -218,10 +218,8 @@ static struct dma_fence *ethosu_job_run(struct drm_sched_job *sched_job)
ethosu_switch_perfmon(dev, job);
scoped_guard(mutex, &dev->job_lock) {
dev->in_flight_job = job;
ethosu_job_hw_submit(dev, job);
}
WRITE_ONCE(dev->in_flight_job, job);
ethosu_job_hw_submit(dev, job);
return fence;
}
@@ -229,6 +227,7 @@ static struct dma_fence *ethosu_job_run(struct drm_sched_job *sched_job)
static void ethosu_job_handle_irq(struct ethosu_device *dev)
{
u32 status = readl_relaxed(dev->regs + NPU_REG_STATUS);
struct ethosu_job *job;
if (status & (STATUS_BUS_STATUS | STATUS_CMD_PARSE_ERR)) {
dev_err(dev->base.dev, "Error IRQ - %x\n", status);
@@ -236,11 +235,10 @@ static void ethosu_job_handle_irq(struct ethosu_device *dev)
return;
}
scoped_guard(mutex, &dev->job_lock) {
if (dev->in_flight_job) {
dma_fence_signal(dev->in_flight_job->done_fence);
dev->in_flight_job = NULL;
}
job = READ_ONCE(dev->in_flight_job);
if (job) {
WRITE_ONCE(dev->in_flight_job, NULL);
dma_fence_signal(job->done_fence);
}
}
@@ -296,8 +294,7 @@ static enum drm_gpu_sched_stat ethosu_job_timedout(struct drm_sched_job *bad)
drm_sched_stop(&dev->sched, bad);
scoped_guard(mutex, &dev->job_lock)
dev->in_flight_job = NULL;
WRITE_ONCE(dev->in_flight_job, NULL);
/* Proceed with reset now. */
pm_runtime_force_suspend(dev->base.dev);
@@ -328,9 +325,6 @@ int ethosu_job_init(struct ethosu_device *edev)
int ret;
spin_lock_init(&edev->fence_lock);
ret = devm_mutex_init(dev, &edev->job_lock);
if (ret)
return ret;
ret = devm_mutex_init(dev, &edev->sched_lock);
if (ret)
return ret;