[PATCH] media: rkisp1: Reduce min_queued_buffers to 1

[Sebastian Fricke]

On 07.10.2024 22:49, Laurent Pinchart wrote:
>On Mon, Oct 07, 2024 at 09:35:49PM +0200, Jacopo Mondi wrote:
>> 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 ?
>
>I find it clear enough, I prefer dropping the macro as you do in this
>patch.

Sounds good.

>
>> > > > 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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