[PATCH] media: rkisp1: Reduce min_queued_buffers to 1

[Jacopo Mondi]

Hi Sebastian,

On Mon, Oct 07, 2024 at 04:05:01PM GMT, Sebastian Fricke wrote:
> On 07.10.2024 16:47, Laurent Pinchart wrote:
> > On Mon, Oct 07, 2024 at 02:57:30PM +0200, Sebastian Fricke wrote:
> > > Hey Jacopo,
> > >
> > > On 07.10.2024 14:42, 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
> > > > 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;
> > >
> > > It looks like RKISP1_MIN_BUFFERS_NEEDED is used only here, so can you
> > > remove the define as well?
> >
> > Isn't that exactly what this patch is doing ?
>
> Oh *facepalm* ... I missed that please disregard ...
>
> but my question below remains whether to not just change the value.

Do you mean

-#define RKISP1_MIN_BUFFERS_NEEDED 3
+#define RKISP1_MIN_BUFFERS_NEEDED 1

?

I would rather avoid defining a value used in a single place. If it
was some magic number a macro name would maybe help giving come
context, but considering this is assigned to min_queued_buffers it's
imho clear enough ?

>
> Sorry,
> Sebastian
>
> >
> > > rg 'RKISP1_MIN_BUFFERS_NEEDED'
> > > drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
> > > 38:#define RKISP1_MIN_BUFFERS_NEEDED 3
> > > 1566:	q->min_queued_buffers = RKISP1_MIN_BUFFERS_NEEDED;
> > >
> > > Or maybe just change the value, but I am not sure whether this can be
> > > considered a magic value.
> > >
> > > > +	q->min_queued_buffers = 1;
> > > >  	q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> > > >  	q->lock = &node->vlock;
> > > >  	q->dev = cap->rkisp1->dev;
> >
> > --
> > Regards,
> >
> > Laurent Pinchart
> Sebastian Fricke
> Consultant Software Engineer
>
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