media: v4l2-mem2mem: reorder checks in v4l2_m2m_poll()

When reaching the end of stream, V4L2 m2m clients may expect the
V4L2_EOS_EVENT. Although the V4L2_EOS_EVENT is deprecated behavior,
drivers must signal that event before dequeuing the buffer that has the
V4L2_BUF_FLAG_LAST flag set.

If a driver queues the V4L2_EOS_EVENT event and returns the buffer after
the check for events but before the check for buffers, vb2_m2m_poll()
will signal that the buffer with V4L2_BUF_FLAG_LAST can be read but not
that the V4L2_EOS_EVENT is available.

Split the check for buffers into a separate function and check for
available buffers before checking for events. This ensures that if
vb2_m2m_poll() signals POLLIN | POLLRDNORM for the V4L2_BUF_FLAG_LAST
buffer, it signals POLLPRI for the V4L2_EOS_EVENT, too.
Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil-cisco@xs4all.nl: fix checkpatch alignment warning]
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/v4l2-core/v4l2-mem2mem.c

@@ -603,11 +603,10 @@ int v4l2_m2m_streamoff(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 }
 EXPORT_SYMBOL_GPL(v4l2_m2m_streamoff);
 
-__poll_t v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
-			   struct poll_table_struct *wait)
+static __poll_t v4l2_m2m_poll_for_data(struct file *file,
+				       struct v4l2_m2m_ctx *m2m_ctx,
+				       struct poll_table_struct *wait)
 {
-	struct video_device *vfd = video_devdata(file);
-	__poll_t req_events = poll_requested_events(wait);
 	struct vb2_queue *src_q, *dst_q;
 	struct vb2_buffer *src_vb = NULL, *dst_vb = NULL;
 	__poll_t rc = 0;
@@ -619,16 +618,6 @@ __poll_t v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 	poll_wait(file, &src_q->done_wq, wait);
 	poll_wait(file, &dst_q->done_wq, wait);
 
-	if (test_bit(V4L2_FL_USES_V4L2_FH, &vfd->flags)) {
-		struct v4l2_fh *fh = file->private_data;
-
-		poll_wait(file, &fh->wait, wait);
-		if (v4l2_event_pending(fh))
-			rc = EPOLLPRI;
-		if (!(req_events & (EPOLLOUT | EPOLLWRNORM | EPOLLIN | EPOLLRDNORM)))
-			return rc;
-	}
-
 	/*
 	 * There has to be at least one buffer queued on each queued_list, which
 	 * means either in driver already or waiting for driver to claim it
@@ -637,10 +626,8 @@ __poll_t v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 	if ((!src_q->streaming || src_q->error ||
 	     list_empty(&src_q->queued_list)) &&
 	    (!dst_q->streaming || dst_q->error ||
-	     list_empty(&dst_q->queued_list))) {
-		rc |= EPOLLERR;
-		goto end;
-	}
+	     list_empty(&dst_q->queued_list)))
+		return EPOLLERR;
 
 	spin_lock_irqsave(&dst_q->done_lock, flags);
 	if (list_empty(&dst_q->done_list)) {
@@ -650,7 +637,7 @@ __poll_t v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 		 */
 		if (dst_q->last_buffer_dequeued) {
 			spin_unlock_irqrestore(&dst_q->done_lock, flags);
-			return rc | EPOLLIN | EPOLLRDNORM;
+			return EPOLLIN | EPOLLRDNORM;
 		}
 	}
 	spin_unlock_irqrestore(&dst_q->done_lock, flags);
@@ -673,7 +660,27 @@ __poll_t v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
 		rc |= EPOLLIN | EPOLLRDNORM;
 	spin_unlock_irqrestore(&dst_q->done_lock, flags);
 
-end:
+	return rc;
+}
+
+__poll_t v4l2_m2m_poll(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
+		       struct poll_table_struct *wait)
+{
+	struct video_device *vfd = video_devdata(file);
+	__poll_t req_events = poll_requested_events(wait);
+	__poll_t rc = 0;
+
+	if (req_events & (EPOLLOUT | EPOLLWRNORM | EPOLLIN | EPOLLRDNORM))
+		rc = v4l2_m2m_poll_for_data(file, m2m_ctx, wait);
+
+	if (test_bit(V4L2_FL_USES_V4L2_FH, &vfd->flags)) {
+		struct v4l2_fh *fh = file->private_data;
+
+		poll_wait(file, &fh->wait, wait);
+		if (v4l2_event_pending(fh))
+			rc |= EPOLLPRI;
+	}
+
 	return rc;
 }
 EXPORT_SYMBOL_GPL(v4l2_m2m_poll);