On Sat, Oct 11, 2014 at 01:37:55AM +0530, Sumit Semwal wrote:
At present, struct device lacks a mechanism of exposing memory
access constraints for the device.
Consequently, there is also no mechanism to share these constraints
while sharing buffers using dma-buf.
If we add support for sharing such constraints, we could use that
to try to collect requirements of different buffer-sharing devices
to allocate buffers from a pool that satisfies requirements of all
This is an attempt to add this support; at the moment, only a bitmask
is added, but if post discussion, we realise we need more information,
we could always extend the definition of constraint.
A new dma-buf op is also added, to allow exporters to interpret or decide
on constraint-masks on their own. A default implementation is provided to
just AND (&) all the constraint-masks.
What constitutes a constraint-mask could be left for interpretation on a
per-platform basis, while defining some common masks.
Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Just a few high-level comments, I'm between conference travel but
hopefully I can discuss this a bit at plumbers next week.
- I agree that for the insane specific cases we need something opaque like
the access constraints mask you propose here. But for the normal case I
think the existing dma constraints in dma_params would go a long way,
and I think we should look at Rob's RFC from aeons ago to solve those:
With this we should be able to cover the allocation constraints of 90%
of all cases hopefully.
- I'm not sure whether an opaque bitmask is good enough really, I suspect
that we also need various priorities between different allocators. With
the option that some allocators are flat-out incompatible.