Re: [PATCH] [media] hdmi: added functions for MPEG InfoFrames

[Thierry Reding]

On Sat, Nov 14, 2015 at 07:38:19PM +0100, Enric Balletbo i Serra wrote:
> The MPEG Source (MS) InfoFrame is in EIA/CEA-861B. It describes aspects of
> the compressed video stream that were used to produce the uncompressed
> video.
> 
> The patch adds functions to work with MPEG InfoFrames.
> 
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
> ---
>  drivers/video/hdmi.c | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/hdmi.h |  24 ++++++++
>  2 files changed, 180 insertions(+)

According to the CEA specification a source is expected to send this
type of infoframe once per video frame. I'm curious how you envision
this to be ensured. Would hardware provide a mechanism to store this
data and send the infoframe automatically? How would you ensure that
updates sent to the hardware match the upcoming frame?

> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
[...]
> @@ -435,6 +510,8 @@ hdmi_infoframe_pack(union hdmi_infoframe *frame, void *buffer, size_t size)
>  		length = hdmi_vendor_any_infoframe_pack(&frame->vendor,
>  							buffer, size);
>  		break;
> +	case HDMI_INFOFRAME_TYPE_MPEG:
> +		length = hdmi_mpeg_infoframe_pack(&frame->mpeg, buffer, size);

Missing "break;"?

> @@ -899,6 +978,41 @@ static void hdmi_audio_infoframe_log(const char *level,
>  			frame->downmix_inhibit ? "Yes" : "No");
>  }
>  
> +static const char *hdmi_mpeg_picture_get_name(enum hdmi_mpeg_picture_type type)
> +{
> +	switch (type) {
> +	case HDMI_MPEG_PICTURE_TYPE_UNKNOWN:
> +		return "Unknown";
> +	case HDMI_MPEG_PICTURE_TYPE_I:
> +		return "Intra-coded picture";
> +	case HDMI_MPEG_PICTURE_TYPE_B:
> +		return "Bi-predictive picture";
> +	case HDMI_MPEG_PICTURE_TYPE_P:
> +		return "Predicted picture";
> +	}

I'd have chosen the slightly more canonical "I-Frame", "P-Frame",
"B-Frame" here, but that's not a strong objection.

> +	return "Reserved";

There really can't be another value here, so I think this should either
return NULL or even go as far as let it crash. There should be no way
for the invalid value to make it this far.

> +static int hdmi_mpeg_infoframe_unpack(struct hdmi_mpeg_infoframe *frame,
> +				     void *buffer)
> +{
> +	u8 *ptr = buffer;
> +
> +	if (ptr[0] != HDMI_INFOFRAME_TYPE_MPEG ||
> +	    ptr[1] != 1 ||
> +	    ptr[2] != HDMI_MPEG_INFOFRAME_SIZE) {
> +		return -EINVAL;
> +	}

There's no need for the braces here.

> @@ -314,6 +336,7 @@ union hdmi_vendor_any_infoframe {
>   * @spd: spd infoframe
>   * @vendor: union of all vendor infoframes
>   * @audio: audio infoframe
> + * @mpeg: mpeg infoframe

s/mpeg/MPEG/

Thierry

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