[PATCH 6.6.y] media: nxp: imx8-isi: Reduce minimum queued buffers from 2 to 0

[Sasha Levin <sashal@kernel.org>]

From: Guoniu Zhou <guoniu.zhou@nxp.com>

[ Upstream commit 2f38622d0f85f317be9e6b131da6cd511db94fd2 ]

Fix a hang issue when capturing a single frame with applications like cam
in libcamera. It would hang waiting for the driver to complete the buffer,
but streaming never starts because min_queued_buffers was set to 2.

The ISI module uses a ping-pong buffer mechanism that requires two buffers
to be programmed at all times. However, when fewer than 2 user buffers are
available, the driver use internal discard buffers to fill the remaining
slot(s). Reduce minimum queued buffers from 2 to 0 allows streaming to
start without any queued buffers.

Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
Cc: stable@vger.kernel.org
Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patch.msgid.link/20260312-isi_min_buffers-v2-1-d5ea1c79ad81@nxp.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
[ renamed `min_queued_buffers` to `min_buffers_needed` ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 2 +-
 1 file changed, 1 insertion(+), 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 111be77eca1ca..f4a9f130e3cf6 100644
--- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
+++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
@@ -1456,7 +1456,7 @@ int mxc_isi_video_register(struct mxc_isi_pipe *pipe,
 	q->mem_ops = &vb2_dma_contig_memops;
 	q->buf_struct_size = sizeof(struct mxc_isi_buffer);
 	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
-	q->min_buffers_needed = 2;
+	q->min_buffers_needed = 0;
 	q->lock = &video->lock;
 	q->dev = pipe->isi->dev;
 
-- 
2.53.0