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

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hello Guoniu

On Wed, Mar 11, 2026 at 04:02:58PM +0800, Guoniu Zhou wrote:
> From: Guoniu Zhou <guoniu.zhou@nxp.com>
>
> 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 1 allows streaming to

Does it mean the ISI can use internal buffer discard for both buffer
slots ? Can we make min_queued_buffers == 0 ?

> start with a single buffer providing more flexibility for applications.
>
> Signed-off-by: Guoniu Zhou <guoniu.zhou@nxp.com>
> ---
>  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..2405baf21594cd18cf2b349234313c5e103b7802 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 = 1;
>  	q->lock = &video->lock;
>  	q->dev = pipe->isi->dev;
>
>
> --
> 2.34.1
>
>