[PATCH] media: rkisp1: Reduce min_queued_buffers to 1

[Laurent Pinchart]

Hi Jacopo,

Thank you for the patch.

On Mon, Oct 07, 2024 at 02:42:24PM +0200, Jacopo Mondi wrote:
> There apparently is no reason to require 3 queued buffers to call
> streamon() for the RkISP1 as the driver operates with a scratch buffer
> where frames can be directed to if there's no available buffer provided
> by userspace.
> 
> Reduce the number of required buffers to 1 to allow applications to
> operate with a single queued buffer.
> 
> Tested with libcamera, by operating with a single capture a request. The

s/capture a/capture/

> same request (and associated capture buffer) gets recycled once
> completed. This of course causes a frame rate drop but doesn't hinder
> operations.
> 
> Signed-off-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>
> ---
> 
> Adam,
>    a few months ago you were exercizing your pinhole app with a single capture
> request for StillCapture operations and you got the video device to hang because
> no enough buffers where provided.
> 	
> This small change should be enough to unblock you. Could you maybe give it a
> spin if you're still working on this ?
> 
> Thanks
>    j
> ---
> 
>  drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c b/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
> index 2bddb4fa8a5c..34adaecdee54 100644
> --- a/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
> +++ b/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
> @@ -35,8 +35,6 @@
>  #define RKISP1_SP_DEV_NAME	RKISP1_DRIVER_NAME "_selfpath"
>  #define RKISP1_MP_DEV_NAME	RKISP1_DRIVER_NAME "_mainpath"
> 
> -#define RKISP1_MIN_BUFFERS_NEEDED 3
> -
>  enum rkisp1_plane {
>  	RKISP1_PLANE_Y	= 0,
>  	RKISP1_PLANE_CB	= 1,
> @@ -1563,7 +1561,7 @@ static int rkisp1_register_capture(struct rkisp1_capture *cap)
>  	q->ops = &rkisp1_vb2_ops;
>  	q->mem_ops = &vb2_dma_contig_memops;
>  	q->buf_struct_size = sizeof(struct rkisp1_buffer);
> -	q->min_queued_buffers = RKISP1_MIN_BUFFERS_NEEDED;
> +	q->min_queued_buffers = 1;

min_queued_buffers controls two things in vb2:

- It controls the minimum number of buffers that can be allocated, by
  setting

        if (q->min_reqbufs_allocation < q->min_queued_buffers + 1)
                q->min_reqbufs_allocation = q->min_queued_buffers + 1;

  in vb2_core_queue_init(). Note that this ony impacts the
  VIDIOC_REQBUFS ioctl, VIDIOC_CREATE_BUFS can still allocate a lower
  number of buffers.

- It delays the .start_streaming() call until min_queued_buffers buffers
  have been queued.

This patch brings a clear improvement as it allows operating with a
single buffer. Ideally though, it would be nice to set
min_queued_buffers to 0, so that .start_streaming() gets called
synchronously with VIDIOC_STREAMON. Otherwise stream start errors can be
reported later, at VIDIOC_QBUF time.

I expect going for 0 will require more changes in the driver, so I'm
fine merging this patch as-is as a first step.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>  	q->lock = &node->vlock;
>  	q->dev = cap->rkisp1->dev;

-- 
Regards,

Laurent Pinchart