linux-kernel - [PATCH 2/2] media: v4l2-mem2mem: simplify poll logic a bit

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Message-Id: <20200825145556.637323-3-gnurou@gmail.com>
Date:   Tue, 25 Aug 2020 23:55:56 +0900
From:   Alexandre Courbot <gnurou@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexandre Courbot <gnurou@...il.com>
Subject: [PATCH 2/2] media: v4l2-mem2mem: simplify poll logic a bit

Factorize redundant checks into a single code block, remove the early
return, and declare variables in their innermost block. Hopefully this
makes this code a little bit easier to follow.

Signed-off-by: Alexandre Courbot <gnurou@...il.com>
---
 drivers/media/v4l2-core/v4l2-mem2mem.c | 35 +++++++++++---------------
 1 file changed, 15 insertions(+), 20 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
index 0d0192119af20..aeac9707123d0 100644
--- a/drivers/media/v4l2-core/v4l2-mem2mem.c
+++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
@@ -841,7 +841,6 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
 				       struct poll_table_struct *wait)
 {
 	struct vb2_queue *src_q, *dst_q;
-	struct vb2_buffer *src_vb = NULL, *dst_vb = NULL;
 	__poll_t rc = 0;
 	unsigned long flags;
 
@@ -863,33 +862,29 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
 		return EPOLLERR;
 
 	spin_lock_irqsave(&src_q->done_lock, flags);
-	if (!list_empty(&src_q->done_list))
-		src_vb = list_first_entry(&src_q->done_list, struct vb2_buffer,
-						done_entry);
-	if (src_vb && (src_vb->state == VB2_BUF_STATE_DONE
-			|| src_vb->state == VB2_BUF_STATE_ERROR))
-		rc |= EPOLLOUT | EPOLLWRNORM;
+	if (!list_empty(&src_q->done_list)) {
+		struct vb2_buffer *src_vb = list_first_entry(
+			&src_q->done_list, struct vb2_buffer, done_entry);
+		if (src_vb->state == VB2_BUF_STATE_DONE ||
+		    src_vb->state == VB2_BUF_STATE_ERROR)
+			rc |= EPOLLOUT | EPOLLWRNORM;
+	}
 	spin_unlock_irqrestore(&src_q->done_lock, flags);
 
 	spin_lock_irqsave(&dst_q->done_lock, flags);
-	if (list_empty(&dst_q->done_list)) {
+	if (!list_empty(&dst_q->done_list)) {
+		struct vb2_buffer *dst_vb = list_first_entry(
+			&dst_q->done_list, struct vb2_buffer, done_entry);
+		if (dst_vb->state == VB2_BUF_STATE_DONE ||
+		    dst_vb->state == VB2_BUF_STATE_ERROR)
+			rc |= EPOLLIN | EPOLLRDNORM;
+	} else if (dst_q->last_buffer_dequeued) {
 		/*
 		 * If the last buffer was dequeued from the capture queue,
 		 * return immediately. DQBUF will return -EPIPE.
 		 */
-		if (dst_q->last_buffer_dequeued) {
-			spin_unlock_irqrestore(&dst_q->done_lock, flags);
-			rc |= EPOLLIN | EPOLLRDNORM;
-			return rc;
-		}
-	}
-
-	if (!list_empty(&dst_q->done_list))
-		dst_vb = list_first_entry(&dst_q->done_list, struct vb2_buffer,
-						done_entry);
-	if (dst_vb && (dst_vb->state == VB2_BUF_STATE_DONE
-			|| dst_vb->state == VB2_BUF_STATE_ERROR))
 		rc |= EPOLLIN | EPOLLRDNORM;
+	}
 	spin_unlock_irqrestore(&dst_q->done_lock, flags);
 
 	return rc;
-- 
2.28.0