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

[Ricardo Ribalda Delgado]

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

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 by poll, due to a previous check.

Reported-by: Dimitrios Katsaros <patcherwork@xxxxxxxxx>
Cc: Junghak Sung <jh1009.sung@xxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 49d8ab9feaf2 ("media] media: videobuf2: Separate vb2_poll()")
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@xxxxxxxxx>
---
 drivers/media/v4l2-core/videobuf2-core.c | 8 ++++++++
 drivers/media/v4l2-core/videobuf2-v4l2.c | 8 --------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 5d016f496e0e..199c65dbe330 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -2298,6 +2298,14 @@ unsigned int vb2_core_poll(struct vb2_queue *q, struct file *file,
 		return POLLERR;
 
 	/*
+	 * 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;
+
+	/*
 	 * 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 91f552124050..c9bad9ef2104 100644
--- a/drivers/media/v4l2-core/videobuf2-v4l2.c
+++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
@@ -818,14 +818,6 @@ 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);
-- 
2.8.0.rc3