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

[Jason Ekstrand]

+Nanley

We've not defined those yet.  We had some internal talks a couple
years ago.  The rough idea we had at the time was to define a modifier
for those cases which put the CCS after each main surface at some
fixed calculation offset based on width, height, and stride.  Then the
one modifier would apply independently to the three different planes.

--Jason

On Wed, Jun 9, 2021 at 2:11 PM Chad Versace <chad at kiwitree.net> wrote:
>
> 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.