On 28/06/2024 15:55, Boris Brezillon wrote:
> A sync-only job is meant to provide a synchronization point on a
> queue, so we can't return a NULL fence there, we have to add a signal
> operation to the command stream which executes after all other
> previously submitted jobs are done.
>
> Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Looks correct to me.
Reviewed-by: Steven Price <steven.price@xxxxxxx>
> ---
> drivers/gpu/drm/panthor/panthor_sched.c | 41 ++++++++++++++++++++-----
> include/uapi/drm/panthor_drm.h | 5 +++
> 2 files changed, 38 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 79ffcbc41d78..951ff7e63ea8 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -458,6 +458,16 @@ struct panthor_queue {
> /** @seqno: Sequence number of the last initialized fence. */
> atomic64_t seqno;
>
> + /**
> + * @last_fence: Fence of the last submitted job.
> + *
> + * We return this fence when we get an empty command stream.
> + * This way, we are guaranteed that all earlier jobs have completed
> + * when drm_sched_job::s_fence::finished without having to feed
> + * the CS ring buffer with a dummy job that only signals the fence.
> + */
> + struct dma_fence *last_fence;
> +
> /**
> * @in_flight_jobs: List containing all in-flight jobs.
> *
> @@ -829,6 +839,9 @@ static void group_free_queue(struct panthor_group *group, struct panthor_queue *
> panthor_kernel_bo_destroy(queue->ringbuf);
> panthor_kernel_bo_destroy(queue->iface.mem);
>
> + /* Release the last_fence we were holding, if any. */
> + dma_fence_put(queue->fence_ctx.last_fence);
> +
> kfree(queue);
> }
>
> @@ -2865,11 +2878,14 @@ queue_run_job(struct drm_sched_job *sched_job)
> static_assert(sizeof(call_instrs) % 64 == 0,
> "call_instrs is not aligned on a cacheline");
>
> - /* Stream size is zero, nothing to do => return a NULL fence and let
> - * drm_sched signal the parent.
> + /* Stream size is zero, nothing to do except making sure all previously
> + * submitted jobs are done before we signal the
> + * drm_sched_job::s_fence::finished fence.
> */
> - if (!job->call_info.size)
> - return NULL;
> + if (!job->call_info.size) {
> + job->done_fence = dma_fence_get(queue->fence_ctx.last_fence);
> + return job->done_fence;
> + }
>
> ret = pm_runtime_resume_and_get(ptdev->base.dev);
> if (drm_WARN_ON(&ptdev->base, ret))
> @@ -2928,6 +2944,10 @@ queue_run_job(struct drm_sched_job *sched_job)
> }
> }
>
> + /* Update the last fence. */
> + dma_fence_put(queue->fence_ctx.last_fence);
> + queue->fence_ctx.last_fence = dma_fence_get(job->done_fence);
> +
> done_fence = dma_fence_get(job->done_fence);
>
> out_unlock:
> @@ -3378,10 +3398,15 @@ panthor_job_create(struct panthor_file *pfile,
> goto err_put_job;
> }
>
> - job->done_fence = kzalloc(sizeof(*job->done_fence), GFP_KERNEL);
> - if (!job->done_fence) {
> - ret = -ENOMEM;
> - goto err_put_job;
> + /* Empty command streams don't need a fence, they'll pick the one from
> + * the previously submitted job.
> + */
> + if (job->call_info.size) {
> + job->done_fence = kzalloc(sizeof(*job->done_fence), GFP_KERNEL);
> + if (!job->done_fence) {
> + ret = -ENOMEM;
> + goto err_put_job;
> + }
> }
>
> ret = drm_sched_job_init(&job->base,
> diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
> index aaed8e12ad0b..926b1deb1116 100644
> --- a/include/uapi/drm/panthor_drm.h
> +++ b/include/uapi/drm/panthor_drm.h
> @@ -802,6 +802,9 @@ struct drm_panthor_queue_submit {
> * Must be 64-bit/8-byte aligned (the size of a CS instruction)
> *
> * Can be zero if stream_addr is zero too.
> + *
> + * When the stream size is zero, the queue submit serves as a
> + * synchronization point.
> */
> __u32 stream_size;
>
> @@ -822,6 +825,8 @@ struct drm_panthor_queue_submit {
> * ensure the GPU doesn't get garbage when reading the indirect command
> * stream buffers. If you want the cache flush to happen
> * unconditionally, pass a zero here.
> + *
> + * Ignored when stream_size is zero.
> */
> __u32 latest_flush;
>
