Re: [PATCH v7 6/9] media: Add parsing for APP14 data segment in jpeg helpers

[Philipp Zabel]

On Mon, 2021-01-11 at 21:28 +0200, Mirela Rabulea wrote:
> From: Mirela Rabulea <mirela.rabulea@xxxxxxx>
> 
> According to Rec. ITU-T T.872 (06/2012) 6.5.3
> APP14 segment is for color encoding, it contains a transform flag, which
> may have values of 0, 1 and 2 and are interpreted as follows:
> 0 - CMYK for images that are encoded with four components
>   - RGB for images that are encoded with three components
> 1 - An image encoded with three components using YCbCr colour encoding.
> 2 - An image encoded with four components using YCCK colour encoding.
> 
> This is used in imx-jpeg decoder, to distinguish between
> YUV444 and RGB24.
> 
> Signed-off-by: Mirela Rabulea <mirela.rabulea@xxxxxxx>
> ---
> Changes in v7:
>   Check there are 6 bytes available in the stream before checking for "Adobe\0"
>   Change jpeg_parse_app14_data function to differentiate between the 3 scenarios: app14 missing, or app14 present but with/without parsing errors:
>     App14 missing => Added V4L2_JPEG_APP14_TF_UNKNOWN to the enum v4l2_jpeg_app14_tf, use it to indicate app14 & TF is missing
> 	App14 present without parsing errors => Return the transform flag value as enum v4l2_jpeg_app14_tf (new paramater of jpeg_parse_app14_data function)
>     App14 present with parsing errors => Return -EINVAL from jpeg_parse_app14_data, also return from calling function (v4l2_jpeg_parse_header) when this error is met.
>
>  drivers/media/v4l2-core/v4l2-jpeg.c | 47 +++++++++++++++++++++++++++--
>  include/media/v4l2-jpeg.h           | 20 ++++++++++++
>  2 files changed, 65 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-jpeg.c b/drivers/media/v4l2-core/v4l2-jpeg.c
> index 8947fd95c6f1..8d5fedb136dd 100644
> --- a/drivers/media/v4l2-core/v4l2-jpeg.c
> +++ b/drivers/media/v4l2-core/v4l2-jpeg.c
> @@ -45,6 +45,7 @@ MODULE_LICENSE("GPL");
>  #define DHP	0xffde	/* hierarchical progression */
>  #define EXP	0xffdf	/* expand reference */
>  #define APP0	0xffe0	/* application data */
> +#define APP14	0xffee	/* application data for colour encoding */
>  #define APP15	0xffef
>  #define JPG0	0xfff0	/* extensions */
>  #define JPG13	0xfffd
> @@ -444,8 +445,44 @@ static int jpeg_skip_segment(struct jpeg_stream *stream)
>  	return jpeg_skip(stream, len - 2);
>  }
>  
> +/* Rec. ITU-T T.872 (06/2012) 6.5.3 */
> +static int jpeg_parse_app14_data(struct jpeg_stream *stream,
> +				 enum v4l2_jpeg_app14_tf *tf)
> +{
> +	int ret;
> +	int lp;
> +	int skip;
> +
> +	lp = jpeg_get_word_be(stream);
> +	if (lp < 0)
> +		return lp;
> +
> +	/* Check for "Adobe\0" in Ap1..6 */
> +	if (stream->curr + 6 > stream->end ||
> +	    strncmp(stream->curr, "Adobe\0", 6))
> +		return -EINVAL;
> +
> +	/* get to Ap12 */
> +	ret = jpeg_skip(stream, 11);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = jpeg_get_byte(stream);
> +	if (ret < 0)
> +		return ret;
> +
> +	*tf = ret;
> +
> +	skip = lp - 2 - 11;

> +	ret = jpeg_skip(stream, skip);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;

This could be simplified to

	return jpeg_skip(stream, skip);

although it would be better style to move the *tf = ... assignment down
past the last error return instead. Either way,

Reviewed-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>

regards
Philipp