[media] media: vb2: Fix regression on poll() for RW mode

When using a device is read/write mode, vb2 does not handle properly the
first select/poll operation.

The reason for this, is that when this code has been refactored, some of
the operations have changed their order, and now fileio emulator is not
started.

The reintroduced check to the core is enabled by a quirk flag, that
avoids this check by other subsystems like DVB.

Fixes: 49d8ab9feaf2 ("media] media: videobuf2: Separate vb2_poll()")

Reported-by: Dimitrios Katsaros <patcherwork@gmail.com>
Cc: Junghak Sung <jh1009.sung@samsung.com>
Cc: <stable@vger.kernel.org>      # for v4.5 and up
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

2 files changed, 16 insertions, 8 deletions

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 2169544..9fbcb67 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -2298,6 +2298,16 @@ unsigned int vb2_core_poll(struct vb2_queue *q, struct file *file,
 		return POLLERR;
 
 	/*
+	 * If this quirk is set and QBUF hasn't been called yet then
+	 * return POLLERR as well. This only affects capture queues, output
+	 * queues will always initialize waiting_for_buffers to false.
+	 * This quirk is set by V4L2 for backwards compatibility reasons.
+	 */
+	if (q->quirk_poll_must_check_waiting_for_buffers &&
+	    q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM)))
+		return POLLERR;
+
+	/*
 	 * For output streams you can call write() as long as there are fewer
 	 * buffers queued than there are buffers available.
 	 */
diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
index 8da7470..7f366f1 100644
--- a/drivers/media/v4l2-core/videobuf2-v4l2.c
+++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
@@ -771,6 +771,12 @@ int vb2_queue_init(struct vb2_queue *q)
 	q->is_output = V4L2_TYPE_IS_OUTPUT(q->type);
 	q->copy_timestamp = (q->timestamp_flags & V4L2_BUF_FLAG_TIMESTAMP_MASK)
 			== V4L2_BUF_FLAG_TIMESTAMP_COPY;
+	/*
+	 * For compatibility with vb1: if QBUF hasn't been called yet, then
+	 * return POLLERR as well. This only affects capture queues, output
+	 * queues will always initialize waiting_for_buffers to false.
+	 */
+	q->quirk_poll_must_check_waiting_for_buffers = true;
 
 	return vb2_core_queue_init(q);
 }
@@ -824,14 +830,6 @@ unsigned int vb2_poll(struct vb2_queue *q, struct file *file, poll_table *wait)
 			poll_wait(file, &fh->wait, wait);
 	}
 
-	/*
-	 * For compatibility with vb1: if QBUF hasn't been called yet, then
-	 * return POLLERR as well. This only affects capture queues, output
-	 * queues will always initialize waiting_for_buffers to false.
-	 */
-	if (q->waiting_for_buffers && (req_events & (POLLIN | POLLRDNORM)))
-		return POLLERR;
-
 	return res | vb2_core_poll(q, file, wait);
 }
 EXPORT_SYMBOL_GPL(vb2_poll);