[PATCH] drm/fourcc: add Vivante TS modifiers

[Simon Ser]

On Friday, March 19th, 2021 at 8:06 PM, Lucas Stach <l.stach at pengutronix.de> wrote:

> +/*
> + * Vivante TS (tile-status) buffer modifiers. They can be combined with all of
> + * the color buffer tiling modifiers defined above. When TS is present it's a
> + * separate buffer containing the clear/compression status of each tile. The
> + * modifiers are defined as VIVANTE_MOD_TS_c_s, where c is the color buffer tile
> + * size in bytes covered by one entry in the status buffer and s is the number
> + * of status bits per entry.
> + * We reserve the top 8bits of the Vivante modifier space for TS modifiers, as
> + * future cores might add some more TS layout variations.
> + */
> +#define VIVANTE_MOD_TS_64_4               (1ULL << 48)
> +#define VIVANTE_MOD_TS_64_2               (2ULL << 48)
> +#define VIVANTE_MOD_TS_128_4              (3ULL << 48)
> +#define VIVANTE_MOD_TS_256_4              (4ULL << 48)
> +#define VIVANTE_MOD_TS_MASK               (0xffULL  << 48)

Hm, I think it's the first time we have values you can OR with modifiers to
get a new modifiers. This sounds a little bit dangerous, because all of the
fields don't get through the fourcc_mod_code mask.

Maybe it would be better to define something like this:

    #define DRM_FORMAT_MOD_VIVANTE_TS(color_tiling, ts) \
        fourcc_mod_code(VIVANTE, (color_tiling & 0xFF) | (ts & 0xFF << 48))

And then have defines for all of the possible values for color tiling and ts?