gpu: nvgpu: Add gk20a semaphore APIs

Add semaphore_gk20a.c/h that implement a new semaphore management API
for the gk20a driver. The API introduces two entities, 'semaphore pools'
and 'semaphores'.

Semaphore pools are memory areas dedicated for hosting one or more
semaphores. Typically, one pool equals one 4K page. A semaphore pool
is always mapped to the kernel memory, and it can be mapped and
unmapped to gpu address spaces using gk20a_semaphore_pool_map/unmap.

Semaphores are backed by 16 bytes of memory allocated from a semaphore
pool. The value of a semaphore can be 0=acuired or 1=released. When
allocated, the semaphores are initialized to the acquired state. They
can be released, or their releasing can be waited for by the CPU or GPU.

Semaphores are intended to be used only once, and after they are
released they should be freed so that the slot within the semaphore
pool can be reused. However GPU jobs must take references to the
semaphores that they use (similarly as they take references on memory
buffers that they use) so that the semaphore backing memory is not
reused too soon.

Bug 1450122
Bug 1445450

Change-Id: I3fd35f34ca55035decc3e06a9c0ede20c1d48db9
Signed-off-by: Lauri Peltonen <lpeltonen@nvidia.com>
Reviewed-on: http://git-master/r/374842
Reviewed-by: Arto Merilainen <amerilainen@nvidia.com>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>

0 files changed, 0 insertions, 0 deletions