media: atmel: atmel-isc-base: use mutex to lock awb workq from streaming

The AWB workqueue runs in a kernel thread and needs to be synchronized
w.r.t. the streaming status.
It is possible that streaming is stopped while the AWB workq is running.
In this case it is likely that the check for vb2_start_streaming_called is
done at one point in time, but the AWB computations are done later,
including a call to isc_update_profile, which requires streaming to be
started.
Thus , isc_update_profile will fail if during this operation sequence the
streaming was stopped.
To solve this issue, a mutex is added, that will serialize the awb work and
streaming stopping, with the mention that either streaming is stopped
completely including termination of the last frame is done, and after that
the AWB work can check stream status and stop; either first AWB work is
completed and after that the streaming can stop correctly.
The awb spin lock cannot be used since this spinlock is taken in the same
context and using it in the stop streaming will result in a recursion BUG.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/media/platform/atmel/atmel-isc.h b/drivers/media/platform/atmel/atmel-isc.h
index f9ad7ec6bd13..ff60ba020cb9 100644
--- a/drivers/media/platform/atmel/atmel-isc.h
+++ b/drivers/media/platform/atmel/atmel-isc.h
@@ -218,6 +218,7 @@ struct isc_reg_offsets {
  *
  * @lock:		lock for serializing userspace file operations
  *			with ISC operations
+ * @awb_mutex:		serialize access to streaming status from awb work queue
  * @awb_lock:		lock for serializing awb work queue operations
  *			with DMA/buffer operations
  *
@@ -290,6 +291,7 @@ struct isc_device {
 	struct work_struct	awb_work;
 
 	struct mutex		lock;
+	struct mutex		awb_mutex;
 	spinlock_t		awb_lock;
 
 	struct regmap_field	*pipeline[ISC_PIPE_LINE_NODE_NUM];