[Mesa-dev] Allocator Nouveau driver, Mesa EXT_external_objects, and DRM metadata import interfaces
Miguel Angel Vico
mvicomoya at nvidia.com
Wed Dec 20 16:51:51 UTC 2017
As many of you already know, I've been working with James Jones on the
Generic Device Allocator project lately. He started a discussion thread
some weeks ago seeking feedback on the current prototype of the library
and advice on how to move all this forward, from a prototype stage to
production. For further reference, see:
From the thread above, we came up with very interesting high level
design ideas for one of the currently missing parts in the library:
Usage transitions. That's something I'll personally work on during the
In the meantime, I've been working on putting together an open source
implementation of the allocator mechanisms using the Nouveau driver for
all to be able to play with.
Below I'm seeking feedback on a bunch of changes I had to make to
different components of the graphics stack:
** Allocator **
An allocator driver implementation on top of Nouveau. The current
implementation only handles pitch linear layouts, but that's enough
to have the kmscube port working using the allocator and Nouveau
You can pull these changes from
** Mesa **
James's kmscube port to use the allocator relies on the
EXT_external_objects extension to import allocator allocations to
OpenGL as a texture object. However, the Nouveau implementation of
these mechanisms is missing in Mesa, so I went ahead and added them.
You can pull these changes from
Also, James's kmscube port uses the NVX_unix_allocator_import
extension to attach allocator metadata to texture objects so the
driver knows how to deal with the imported memory.
Note that there isn't a formal spec for this extension yet. For now,
it just serves as an experimental mechanism to import allocator
memory in OpenGL, and attach metadata to texture objects.
You can pull these changes (written on top of the above) from:
** kmscube **
Mostly minor fixes and improvements on top of James's port to use the
allocator. Main thing is the allocator initialization path will use
EGL_MESA_platform_surfaceless if EGLDevice platform isn't supported
by the underlying EGL implementation.
You can pull these changes from:
With all the above you should be able to get kmscube working using the
allocator on top of the Nouveau driver.
Another of the missing pieces before we can move this to production is
importing allocations to DRM FB objects. This is probably one of the
most sensitive parts of the project as it requires modification/addition
of kernel driver interfaces.
At XDC2017, James had several hallway conversations with several people
about this, all having different opinions. I'd like to take this
opportunity to also start a discussion about what's the best option to
create a path to get allocator allocations added as DRM FB objects.
These are the few options we've considered to start with:
A) Have vendor-private ioctls to set properties on GEM objects that
are inherited by the FB objects. This is how our (NVIDIA) desktop
DRM driver currently works. This would require every vendor to add
their own ioctl to process allocator metadata, but the metadata is
actually a vendor-agnostic object more like DRM modifiers. We'd
like to come up with a vendor-agnostic solutions that can be
integrated to core DRM.
B) Add a new drmModeAddFBWithMetadata() command that takes allocator
metadata blobs for each plane of the FB. Some people in the
community have mentioned this is their preferred design. This,
however, means we'd have to go through the exercise of adding
another metadata mechanism to the whole graphics stack.
C) Shove allocator metadata into DRM by defining it to be a separate
plane in the image, and using the existing DRM modifiers mechanism
to indicate there is another plane for each "real" plane added. It
isn't clear how this scales to surfaces that already need several
planes, but there are some people that see this as the only way
forward. Also, we would have to create a separate GEM buffer for
the metadatada itself, which seems excessive.
We personally like option (B) better, and have already started to
prototype the new path (which is actually very similar to the
drmModeAddFB2() one). You can take a look at the new interfaces here:
There may be other options that haven't been explored yet that could be
a better choice than the above, so any suggestion will be greatly
More information about the mesa-dev