So, lucky me, I have a scenario where I get to deal with NV12MT. Hurray!
I know there has been some reluctance in the past to combine tiling and color format, since in theory that could lead to a combinatorial explosion in formats. And, as long as the buffer usage is entirely within a single driver, you can approximately hide tiling (or compressed, etc) permutations of a color format. On the other hand, there is already some precedence for fourcc or format values to represent tiled formats at the interface level (in kernel, v4l, and in userspace, and gstreamer and openmax).
But in this scenario, sharing buffer between other devices (video decoder/encoder) and drm/kms (msm) and mesa (freedreno) via EGL_EXT_image_dma_buf_import[1], I sort of don't really have any other way to pass around tiling flags. So I would propose adding custom fourcc's only in the more limited cases where formats are exchanged between devices. This should avoid an explosion of color_format * tiling_format.
For the kms part, it would mean merging a small patch to allow addfb2 for NV12MT[2].
For the mesa part, it looks like there is a bit of work needed to teach egl about multi-planar buffers, buffers where offset[n] != 0, etc. I'll start with patches to teach egl how to import plain NV12 buffers. But once that is done, for it to be much use to me I'll need NV12MT, which means adding a new gallium format and __DRI_IMAGE_FOURCC_NV12MT.
Also, I'm still a bit undecided on how to represent multi-planar formats (ie. single pipe_resource encapsulating each of the planes? or pipe_resource per plane but teach pipe_sampler_view about textures which have multiple pipe_resource's, one for per plane).
Anyways, I'll start working on the mesa egl bits next week. First step is just add an 'offset' parameter to 'struct winsys_handle', which should hopefully be non-controversial. After that, I need to decide how to handle multi-planar, and I think that hinges on how folks want to handle multi-planar in gallium. Ie. if one pipe_resource per plane, then winsys_handle doesn't need any further change (but we need changes elsewhere), otherwise winsys_handle needs to have an array of handles.
Anyways, I'd appreciate feedback.
BR, -R
[1] https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_im... [2] http://lists.freedesktop.org/archives/dri-devel/2014-July/064828.html