[PATCH RFC 2/4] media: v4l2-mem2mem: Add an optional job_done operation

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

Introduce a new optional job_done operation, which allows calling back
to the driver when a job is done. Since the job might be completed
from interrupt context where some operations are not available, having
a callback from non-atomic context allows performing these operations
upon completion of a job. This is particularly useful for releasing
access to a reference buffer, which cannot be done in atomic context.

Use the already existing v4l2_m2m_device_run_work work queue for that
and clear the M2M device current context after calling job_done in the
worker thread, so that the private data can be passed to the operation.

Delaying the current context clearing should not be a problem since the
next call to v4l2_m2m_try_run happens right after that.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
---
 drivers/media/v4l2-core/v4l2-mem2mem.c | 8 ++++++--
 include/media/v4l2-mem2mem.h           | 4 ++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
index 631f4e2aa942..d5bccb0192f9 100644
--- a/drivers/media/v4l2-core/v4l2-mem2mem.c
+++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
@@ -376,6 +376,11 @@ static void v4l2_m2m_device_run_work(struct work_struct *work)
 	struct v4l2_m2m_dev *m2m_dev =
 		container_of(work, struct v4l2_m2m_dev, job_work);
 
+	if (m2m_dev->m2m_ops->job_done && m2m_dev->curr_ctx)
+		m2m_dev->m2m_ops->job_done(m2m_dev->curr_ctx->priv);
+
+	m2m_dev->curr_ctx = NULL;
+
 	v4l2_m2m_try_run(m2m_dev);
 }
 
@@ -431,8 +436,7 @@ void v4l2_m2m_job_finish(struct v4l2_m2m_dev *m2m_dev,
 	list_del(&m2m_dev->curr_ctx->queue);
 	m2m_dev->curr_ctx->job_flags &= ~(TRANS_QUEUED | TRANS_RUNNING);
 	wake_up(&m2m_dev->curr_ctx->finished);
-	m2m_dev->curr_ctx = NULL;
-
+	/* The current context pointer is cleared after the job_done step. */
 	spin_unlock_irqrestore(&m2m_dev->job_spinlock, flags);
 
 	/* This instance might have more buffers ready, but since we do not
diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
index 43e447dcf69d..261bcd661b2d 100644
--- a/include/media/v4l2-mem2mem.h
+++ b/include/media/v4l2-mem2mem.h
@@ -40,11 +40,15 @@
  *		v4l2_m2m_job_finish() (as if the transaction ended normally).
  *		This function does not have to (and will usually not) wait
  *		until the device enters a state when it can be stopped.
+ * @job_done:	optional. Informs the driver that the current job was completed.
+ *		This can be useful to release access to extra buffers that were
+ *		required for the job, such as reference buffers for decoding.
  */
 struct v4l2_m2m_ops {
 	void (*device_run)(void *priv);
 	int (*job_ready)(void *priv);
 	void (*job_abort)(void *priv);
+	void (*job_done)(void *priv);
 };
 
 struct video_device;
-- 
2.20.1