[PATCH v2 2/2] media: nxp: imx8-isi: Prioritize pending buffers over discard buffers

[Guoniu Zhou]

From: Guoniu Zhou <guoniu.zhou@xxxxxxx>

Change the buffer selection logic to use pending buffers first (up to the
number available), and only use discard buffers to fill remaining slots
when insufficient pending buffers are queued. Ensure user buffers are
utilized as soon as possible, improving efficiency and reducing the number
of discarded frames at stream start.

Signed-off-by: Guoniu Zhou <guoniu.zhou@xxxxxxx>
---
Changes in v2:
- Replace "This ensures" with "ensure"
- Put example from commit message to comment in driver suggested by Frank
  https://lore.kernel.org/linux-media/20260311-isi_min_buffers-v1-0-c9299d6e8ae6@xxxxxxx/T/#m2774912ed31553ef1fdcc840bd6eae53a03ecccd
---
 drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
index 1be3a728f32f89338a75ddcc4e96e7501ed954e1..77ebff03323ace50ff039c8333d25a9c3dd44880 100644
--- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
+++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
@@ -792,7 +792,14 @@ static void mxc_isi_video_queue_first_buffers(struct mxc_isi_video *video)
 		struct mxc_isi_buffer *buf;
 		struct list_head *list;
 
-		list = i < discard ? &video->out_discard : &video->out_pending;
+		/*
+		 * Queue buffers: prioritize pending buffers, then discard buffers
+		 * For example:
+		 * - 2 pending buffers: both slots use pending buffers
+		 * - 1 pending buffer: first slot uses pending, second uses discard
+		 * - 0 pending buffers: both slots use discard buffers
+		 */
+		list = (i < 2 - discard) ? &video->out_pending : &video->out_discard;
 		buf = list_first_entry(list, struct mxc_isi_buffer, list);
 
 		mxc_isi_channel_set_outbuf(video->pipe, buf->dma_addrs, buf_id);

-- 
2.34.1