linux-kernel - Re: [PATCH v2 3/6] media: v4l2-mem2mem: add stateless_(try_)decoder

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Date:   Fri, 4 Oct 2019 11:21:12 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Jernej Skrabec <jernej.skrabec@...l.net>, mchehab@...nel.org,
        paul.kocialkowski@...tlin.com, mripard@...nel.org,
        pawel@...iak.com, m.szyprowski@...sung.com,
        kyungmin.park@...sung.com, tfiga@...omium.org, wens@...e.org
Cc:     gregkh@...uxfoundation.org, boris.brezillon@...labora.com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-arm-kernel@...ts.infradead.org,
        ezequiel@...labora.com, jonas@...boo.se
Subject: Re: [PATCH v2 3/6] media: v4l2-mem2mem: add
 stateless_(try_)decoder_cmd ioctl helpers

On 9/29/19 10:00 PM, Jernej Skrabec wrote:
> These helpers are used by stateless codecs when they support multiple
> slices per frame and hold capture buffer flag is set. It's expected that
> all such codecs will use this code.
> 
> Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> ---
>  drivers/media/v4l2-core/v4l2-mem2mem.c | 35 ++++++++++++++++++++++++++
>  include/media/v4l2-mem2mem.h           |  4 +++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
> index 19937dd3c6f6..2677a07e4c9b 100644
> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> @@ -1154,6 +1154,41 @@ int v4l2_m2m_ioctl_try_decoder_cmd(struct file *file, void *fh,
>  }
>  EXPORT_SYMBOL_GPL(v4l2_m2m_ioctl_try_decoder_cmd);
>  
> +int v4l2_m2m_ioctl_stateless_try_decoder_cmd(struct file *file, void *fh,
> +					     struct v4l2_decoder_cmd *dc)
> +{
> +	if (dc->cmd != V4L2_DEC_CMD_FLUSH)
> +		return -EINVAL;
> +
> +	dc->flags = 0;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_m2m_ioctl_stateless_try_decoder_cmd);
> +
> +int v4l2_m2m_ioctl_stateless_decoder_cmd(struct file *file, void *priv,
> +					 struct v4l2_decoder_cmd *dc)
> +{
> +	struct v4l2_fh *fh = file->private_data;
> +	struct vb2_v4l2_buffer *out_vb, *cap_vb;
> +	int ret;
> +
> +	ret = v4l2_m2m_ioctl_stateless_try_decoder_cmd(file, priv, dc);
> +	if (ret < 0)
> +		return ret;
> +
> +	out_vb = v4l2_m2m_last_src_buf(fh->m2m_ctx);
> +	cap_vb = v4l2_m2m_last_dst_buf(fh->m2m_ctx);

I think this should be v4l2_m2m_next_dst_buf. If multiple capture buffers were
queued up, then it can only be the first capture buffer that can be 'HELD'.

This might solve the race condition you saw with ffmpeg.

Regards,

	Hans

> +
> +	if (out_vb)
> +		out_vb->flags &= ~V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
> +	else if (cap_vb && cap_vb->is_held)
> +		v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_m2m_ioctl_stateless_decoder_cmd);
> +
>  /*
>   * v4l2_file_operations helpers. It is assumed here same lock is used
>   * for the output and the capture buffer queue.
> diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
> index c9fa96c8eed1..8ae2f56c7fa3 100644
> --- a/include/media/v4l2-mem2mem.h
> +++ b/include/media/v4l2-mem2mem.h
> @@ -714,6 +714,10 @@ int v4l2_m2m_ioctl_try_encoder_cmd(struct file *file, void *fh,
>  				   struct v4l2_encoder_cmd *ec);
>  int v4l2_m2m_ioctl_try_decoder_cmd(struct file *file, void *fh,
>  				   struct v4l2_decoder_cmd *dc);
> +int v4l2_m2m_ioctl_stateless_try_decoder_cmd(struct file *file, void *fh,
> +					     struct v4l2_decoder_cmd *dc);
> +int v4l2_m2m_ioctl_stateless_decoder_cmd(struct file *file, void *priv,
> +					 struct v4l2_decoder_cmd *dc);
>  int v4l2_m2m_fop_mmap(struct file *file, struct vm_area_struct *vma);
>  __poll_t v4l2_m2m_fop_poll(struct file *file, poll_table *wait);
>  
>