[PATCH v2 1/2] media: nxp: imx8-isi: Reduce minimum queued buffers from 2 to 0

[Guoniu Zhou]

From: Guoniu Zhou <guoniu.zhou@xxxxxxx>

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@xxxxxxxxxxxxxxx
Signed-off-by: Guoniu Zhou <guoniu.zhou@xxxxxxx>
---
Changes in v2:
- Reduce min_queued_buffers from 2 to 0 suggested by Jacopo Mondi
  https://lore.kernel.org/linux-media/20260311-isi_min_buffers-v1-0-c9299d6e8ae6@xxxxxxx/T/#mcd4b7dcc218a02e2f218ba2c83b947ccefd9308b
- Add fix tag
---
 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 13682bf6e9f8895bb9eb1f92d5f74b0d5968544e..1be3a728f32f89338a75ddcc4e96e7501ed954e1 100644
--- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
+++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
@@ -1410,7 +1410,7 @@ 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_queued_buffers = 2;
+	q->min_queued_buffers = 0;
 	q->lock = &video->lock;
 	q->dev = pipe->isi->dev;
 

-- 
2.34.1