linux-kernel - Re: [PATCH v2 2/2] media: v4l2-mem2mem: simplify poll logic

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Date:   Fri, 28 Aug 2020 12:18:20 -0300
From:   Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
To:     Alexandre Courbot <gnurou@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        linux-media <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] media: v4l2-mem2mem: simplify poll logic

On Thu, 27 Aug 2020 at 09:50, Alexandre Courbot <gnurou@...il.com> wrote:
>
> Factorize redundant checks into a single code block, remove unneeded
> checks (a buffer in done_list is necessarily in the DONE or ERROR
> state), and we end up with a much simpler version of this function.
>
> Signed-off-by: Alexandre Courbot <gnurou@...il.com>

This is really good, thanks!

Reviewed-by: Ezequiel Garcia <ezequiel@...labora.com>

> ---
>  drivers/media/v4l2-core/v4l2-mem2mem.c | 26 +++++---------------------
>  1 file changed, 5 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
> index fe90c3c0e4128..af8138c5d7ced 100644
> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> @@ -841,7 +841,6 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
>                                        struct poll_table_struct *wait)
>  {
>         struct vb2_queue *src_q, *dst_q;
> -       struct vb2_buffer *src_vb = NULL, *dst_vb = NULL;
>         __poll_t rc = 0;
>         unsigned long flags;
>
> @@ -862,32 +861,17 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
>              list_empty(&dst_q->queued_list)))
>                 return EPOLLERR;
>
> -       spin_lock_irqsave(&dst_q->done_lock, flags);
> -       if (list_empty(&dst_q->done_list)) {
> -               /*
> -                * If the last buffer was dequeued from the capture queue,
> -                * return immediately. DQBUF will return -EPIPE.
> -                */
> -               if (dst_q->last_buffer_dequeued)
> -                       rc |= EPOLLIN | EPOLLRDNORM;
> -       }
> -       spin_unlock_irqrestore(&dst_q->done_lock, flags);
> -
>         spin_lock_irqsave(&src_q->done_lock, flags);
>         if (!list_empty(&src_q->done_list))
> -               src_vb = list_first_entry(&src_q->done_list, struct vb2_buffer,
> -                                               done_entry);
> -       if (src_vb && (src_vb->state == VB2_BUF_STATE_DONE
> -                       || src_vb->state == VB2_BUF_STATE_ERROR))
>                 rc |= EPOLLOUT | EPOLLWRNORM;
>         spin_unlock_irqrestore(&src_q->done_lock, flags);
>
>         spin_lock_irqsave(&dst_q->done_lock, flags);
> -       if (!list_empty(&dst_q->done_list))
> -               dst_vb = list_first_entry(&dst_q->done_list, struct vb2_buffer,
> -                                               done_entry);
> -       if (dst_vb && (dst_vb->state == VB2_BUF_STATE_DONE
> -                       || dst_vb->state == VB2_BUF_STATE_ERROR))
> +       /*
> +        * If the last buffer was dequeued from the capture queue, signal
> +        * userspace. DQBUF(CAPTURE) will return -EPIPE.
> +        */
> +       if (!list_empty(&dst_q->done_list) || dst_q->last_buffer_dequeued)
>                 rc |= EPOLLIN | EPOLLRDNORM;
>         spin_unlock_irqrestore(&dst_q->done_lock, flags);
>
> --
> 2.28.0
>