Re: [PATCH v3] media: rkisp1: Remove min_queued_buffers

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Jacopo,

On Thu, Feb 20, 2025 at 03:22:44PM +0100, Jacopo Mondi wrote:
> On Tue, Oct 29, 2024 at 09:21:16AM +0100, Jacopo Mondi wrote:
> > There apparently is no reason to require 3 queued buffers for RkISP1,
> > as the driver operates with a scratch buffer where data can be
> > directed to if there's no available buffer provided by userspace.
> >
> > Reduce the number of required buffers to 0 by removing the
> > initialization of min_queued_buffers, to allow applications to operate
> > by queueing capture buffers on-demand.
> >
> > Tested with libcamera, by operating with a single capture request. The
> > same request (and the 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@ideasonboard.com>
> 
> I just noticed v2 of this series:
> media: rkisp1: Reduce min_queued_buffers to 1
> 
> has been collected instead of this v3.

That's my fault, I apologize.

> And I noticed because a user complained to me about this.
> 
> Now, I can provide an update based on the now merged v2, not a big
> deal, but this depresses me a bit as the discussion about
> implementing multi-commiter model is apparently (again) stalled.
> 
> I know, sh*t happens (TM) and hiccups are expected in the process,
> we all make mistakes and I'm not even sure through which path the
> patch has been collected, but I could have handled this one easily,
> and instead what we have is:
> 
> 1) an unhappy user that will likely have to wait for the next release
> 2) me having to send an additional (rather trivial) patch
> 3) Someone will have to review, collect, PR etc etc
> 
> (and I'm not even mentioning this patch is 3 lines)
> 
> Issues like this one seems to be considered a fact of life we decided
> is fine to live with, while every possible corner case of the proposed
> multi-committer model is analyzed with great concern like we're
> trading a perfect model for something that has to be equally perfect.
> 
> And while I agree the biggest reason for the proverbial v4l2 slow pace
> is the reviewers scarcity and the limited maintainers bandwidth, now
> that we have everything in place to reduce the system clogginess
> it still seems we're not all sold for it. I really don't get it, sorry.

Amen.

> > ---
> > v2->v3:
> > - Remove min_queued_buffers initialization
> >
> > v1->v2:
> > The first version of this patch set min_queued_buffers to 1, but setting it
> > to 0 doesn't compromise operations and it's even better as it allows application
> > to queue buffers to the capture devices on-demand. If a buffer is not provided
> > to the DMA engines, image data gets directed to the driver's internal scratch
> > buffer.
> > ---
> >  drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c | 3 ---
> >  1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c b/drivers/media/platform/rockchip/rkisp1/rkisp1-capture.c
> > index 2bddb4fa8a5c..2f0c610e74b9 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 +1561,6 @@ 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->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> >  	q->lock = &node->vlock;
> >  	q->dev = cap->rkisp1->dev;

-- 
Regards,

Laurent Pinchart

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