[RFC] drm/amdgpu: Add macros and documentation for format modifiers.

[Marek Olšák]

Hopefully this answers some questions.

Other parameters that affect tiling layouts are GB_ADDR_CONFIG (all
chips) and MC_ARB_RAMCFG (GFX6-8 only), and those vary with each chip.

Some 32bpp 1D tiling layouts are compatible across all chips (1D
display tiling is the same as SW_256B_D if Bpp == 4).

On GFX9, swizzle modes <= 11 are the same on all GFX9 chips. The
remaining modes depend on GB_ADDR_CONFIG and are also more efficient.
Bpp, number of samples, and resource type (2D/3D) affect the layout
too, e.g. 3D textures silently use thick tiling on GFX9.

Harvesting doesn't affect tiling layouts.

The layout changes between layers/slices a little. Always use the base
address of the whole image when programming the hardware. Don't assume
that the 2nd layer has the same layout.

> + * TODO: Can scanout really not support fastclear data?

It can, but only those encoded in the DCC buffer (0/1). There is no
DAL support for DCC though.


> + * TODO: Do some generations share DCC format?

DCC mirrors the tiling layout, so the same tiling mode means the same
DCC. Take the absolute pixel address, shift it to the right, and
you'll get the DCC element address.

I would generally consider DCC as non-shareable because of different
meanings of TILING_INDEX between chips except maybe for common GFX9
layouts.


> [comments about number of bits]

We could certainly represent all formats as a list of enums, but then
we would need to convert the enums to the full description in drivers.
GFX6-8 can use TILING_INDEX (except for stencil, let's ignore
stencil). The tiling tables shouldn't change anymore because they are
optimized for the hardware, and later hw doesn't have any tables.

Marek