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References: <20200827124946.328700-1-gnurou@gmail.com> <20200827124946.328700-2-gnurou@gmail.com>
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From:   Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Date:   Fri, 28 Aug 2020 12:17:53 -0300
Message-ID: <CAAEAJfAqB2WAuWd4KKdhxp2=64n=hxkESrzGeBj1KN+Otz7mmg@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] media: v4l2-mem2mem: always consider OUTPUT queue
 during poll
To:     Alexandre Courbot <gnurou@gmail.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Nicolas Dufresne <nicolas.dufresne@collabora.com>,
        linux-media <linux-media@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Thu, 27 Aug 2020 at 09:50, Alexandre Courbot <gnurou@gmail.com> wrote:
>
> If poll() is called on a m2m device with the EPOLLOUT event after the
> last buffer of the CAPTURE queue is dequeued, any buffer available on
> OUTPUT queue will never be signaled because v4l2_m2m_poll_for_data()
> starts by checking whether dst_q->last_buffer_dequeued is set and
> returns EPOLLIN in this case, without looking at the state of the OUTPUT
> queue.
>
> Fix this by not early returning so we keep checking the state of the
> OUTPUT queue afterwards.
>
> Signed-off-by: Alexandre Courbot <gnurou@gmail.com>

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

> ---
>  drivers/media/v4l2-core/v4l2-mem2mem.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
> index 95a8f2dc5341d..fe90c3c0e4128 100644
> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> @@ -868,10 +868,8 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
>                  * If the last buffer was dequeued from the capture queue,
>                  * return immediately. DQBUF will return -EPIPE.
>                  */
> -               if (dst_q->last_buffer_dequeued) {
> -                       spin_unlock_irqrestore(&dst_q->done_lock, flags);
> -                       return EPOLLIN | EPOLLRDNORM;
> -               }
> +               if (dst_q->last_buffer_dequeued)
> +                       rc |= EPOLLIN | EPOLLRDNORM;
>         }
>         spin_unlock_irqrestore(&dst_q->done_lock, flags);
>
> --
> 2.28.0
>