Re: [PATCH v6 2/2] [media] s5p-mfc: Handle 'v4l2_pix_format:field' in try_fmt and g_fmt

[Hans Verkuil <hverkuil@xs4all.nl>]

On 01/03/17 12:51, Thibault Saunier wrote:
> It is required by the standard that the field order is set by the
> driver, default to NONE in case any is provided, but we can basically
> accept any value provided by the userspace as we will anyway not
> be able to do any deinterlacing.
> 
> In this patch we also make sure to pass the interlacing mode provided
> by userspace from the output to the capture side of the device so
> that the information is given back to userspace. This way it can
> handle it and potentially deinterlace afterward.
> 
> Signed-off-by: Thibault Saunier <thibault.saunier@osg.samsung.com>
> 
> ---
> 
> Changes in v6:
> - Pass user output field value to the capture as the device is not
>   doing any deinterlacing and thus decoded content will still be
>   interlaced on the output.
> 
> Changes in v5:
> - Just adapt the field and never error out.
> 
> Changes in v4: None
> Changes in v3:
> - Do not check values in the g_fmt functions as Andrzej explained in previous review
> 
> Changes in v2:
> - Fix a silly build error that slipped in while rebasing the patches
> 
>  drivers/media/platform/s5p-mfc/s5p_mfc_common.h | 2 ++
>  drivers/media/platform/s5p-mfc/s5p_mfc_dec.c    | 6 +++++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_common.h b/drivers/media/platform/s5p-mfc/s5p_mfc_common.h
> index ab23236aa942..3816a37de4bc 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc_common.h
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc_common.h
> @@ -652,6 +652,8 @@ struct s5p_mfc_ctx {
>  	size_t me_buffer_size;
>  	size_t tmv_buffer_size;
>  
> +	enum v4l2_field field;
> +
>  	enum v4l2_mpeg_mfc51_video_force_frame_type force_frame_type;
>  
>  	struct list_head ref_queue;
> diff --git a/drivers/media/platform/s5p-mfc/s5p_mfc_dec.c b/drivers/media/platform/s5p-mfc/s5p_mfc_dec.c
> index 367ef8e8dbf0..6e5ca86fb331 100644
> --- a/drivers/media/platform/s5p-mfc/s5p_mfc_dec.c
> +++ b/drivers/media/platform/s5p-mfc/s5p_mfc_dec.c
> @@ -345,7 +345,7 @@ static int vidioc_g_fmt(struct file *file, void *priv, struct v4l2_format *f)
>  		   rectangle. */
>  		pix_mp->width = ctx->buf_width;
>  		pix_mp->height = ctx->buf_height;
> -		pix_mp->field = V4L2_FIELD_NONE;
> +		pix_mp->field = ctx->field;
>  		pix_mp->num_planes = 2;
>  		/* Set pixelformat to the format in which MFC
>  		   outputs the decoded frame */
> @@ -380,6 +380,9 @@ static int vidioc_try_fmt(struct file *file, void *priv, struct v4l2_format *f)
>  	struct s5p_mfc_dev *dev = video_drvdata(file);
>  	struct s5p_mfc_fmt *fmt;
>  
> +	if (f->fmt.pix.field == V4L2_FIELD_ANY)
> +		f->fmt.pix.field = V4L2_FIELD_NONE;
> +
>  	mfc_debug(2, "Type is %d\n", f->type);
>  	if (f->type == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE) {
>  		fmt = find_format(f, MFC_FMT_DEC);
> @@ -436,6 +439,7 @@ static int vidioc_s_fmt(struct file *file, void *priv, struct v4l2_format *f)
>  		goto out;
>  	} else if (f->type == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE) {
>  		/* src_fmt is validated by call to vidioc_try_fmt */
> +		ctx->field = f->fmt.pix.field;

Doing this means that you also allow for V4L2_FIELD_ALTERNATE. If you do that, then there
are additional requirements when you queue up buffers in that the 'field' has to be set to
TOP or BOTTOM in struct v4l2_buffer. I am sure that is a requirement for the encoder, how
this would work for a decoder I am not sure.

Also, values like V4L2_FIELD_SEQ_TB/BT would not behave well if you pass them through a
decoder.

Frankly I think the only 'reasonable' values would be FIELD_NONE, FIELD_INTERLACED and
possibly FIELD_ALTERNATE. I don't know enough about how codecs handle interlaced formats,
so I can't tell how much sense FIELD_ALTERNATE would make.

Properly supporting interlaced formats should only be done if you actually tested it and
know how it works and what exactly is supported.

Regards,

	Hans

>  		ctx->src_fmt = find_format(f, MFC_FMT_DEC);
>  		ctx->codec_mode = ctx->src_fmt->codec_mode;
>  		mfc_debug(2, "The codec number is: %d\n", ctx->codec_mode);
>