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SubjectRe: [PATCH v2 1/4] media: uapi: hevc: Add scaling matrix control
Em Fri, 13 Dec 2019 17:04:25 +0100
Jernej Skrabec <jernej.skrabec@siol.net> escreveu:

> HEVC has a scaling matrix concept. Add support for it.

> +struct v4l2_ctrl_hevc_scaling_matrix {
> + __u8 scaling_list_4x4[6][16];
> + __u8 scaling_list_8x8[6][64];
> + __u8 scaling_list_16x16[6][64];
> + __u8 scaling_list_32x32[2][64];
> + __u8 scaling_list_dc_coef_16x16[6];
> + __u8 scaling_list_dc_coef_32x32[2];
> +};

I never looked at HEVC spec, but the above seems really weird.

Please correct me if I am wrong, but each of the above matrixes
is independent, and the driver will use just one of the above on
any specific time (for a given video output node), right?

If so, why would userspace be forced to update lots of matrixes, if would
likely use just one at a given time?

IMO, the proper way would be, instead, to use an uAPI like:

/*
* Actually, as this is uAPI, we will use a fixed size integer type, like
* unsigned int
*/
enum hevc_scaling_matrix_type {
HEVC_SCALING_MATRIX_4x4,
HEVC_SCALING_MATRIX_8x8,
...
HEVC_SCALING_MATRIX_DC_COEF_32x32,
};

struct v4l2_ctrl_hevc_scaling_matrix {
__u32 scaling_type /* as defined by enum hevc_scaling_matrix_type */

union {
__u8 scaling_list_4x4[6][16];
__u8 scaling_list_8x8[6][64];
__u8 scaling_list_16x16[6][64];
__u8 scaling_list_32x32[2][64];
__u8 scaling_list_dc_coef_16x16[6];
__u8 scaling_list_dc_coef_32x32[2];
};
};

And let the core use a default for each scaling matrix, if userspace doesn't
set it.



Cheers,
Mauro

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