[Mesa-dev] Intel: ABI for DRM format modifiers with multi-planar images

[Chad Versace]

The Problem: For a given 3-tuple (multi-planar format, DRM format modifier, chipset), we need Intel ABI that decides (a) the value of VkDrmFormatModifierPropertiesEXT::drmFormatModifierPlaneCount and (b) the content of each "modifier" plane.

For example, suppose drmFormatModifierPlaneCount is 2 for (VK_FORMAT_G8_B8R8_2PLANE_420_UNORM, INTEL_FORMAT_MOD_FOO). Is the layout (plane1=g8, plane2=b8r8); or is it (plane1=g8_b8r8, plane2=aux)? The second choice isn't crazy; iirc, some non-Intel hardware (sorry, NDA) uses only 2 modifier planes for color-compressed 3-planar formats, with (plane1=r8_g8_b8, plane2=aux).

I'm asking because Yiwei (cc'd) has begun implementing limited support for multi-planar formats in Anvil in order to pass the Android CTS. To support more media formats (for imminent Chrome OS projects and future vanilla Linux stuff too), we need to decide on some ABI.