tree 690d369e969039a54fec3a813d60b7acf5ea8207
parent 71e8831f6407542afd1d8888d3cca13e677034ef
author Rob Clark <rob@ti.com> 1323134362 -0600
committer Greg Kroah-Hartman <gregkh@suse.de> 1323385461 -0800

drm/omap: add GEM support for tiled/dmm buffers

TILER/DMM provides two features for omapdrm GEM objects:
1) providing a physically contiguous view to discontiguous memory
   for hw initiators that cannot otherwise support discontiguous
   buffers (DSS scanout, IVAHD video decode/encode, etc)
2) providing untiling for 2d tiled buffers, which are used in some
   cases to provide rotation and reduce memory bandwidth for hw
   initiators that tend to access data in 2d block patterns.

For 2d tiled buffers, there are some additional complications when
it comes to userspace mmap'ings.  For non-tiled buffers, the original
(potentially physically discontiguous) pages are used to back the
mmap.  For tiled buffers, we need to mmap via the tiler/dmm region to
provide an unswizzled view of the buffer.  But (a) the buffer is not
necessarily pinned in TILER all the time (it can be unmapped when
there is no DMA access to the buffer), and (b) when they are they
are pinned, they not necessarily page aligned from the perspective of
the CPU.  And non-page aligned userspace buffer mapping is evil.

To solve this, we reserve one or more small regions in each of the 2d
containers when the driver is loaded to use as a "user-GART" where we
can create a second page-aligned mapping of parts of the buffer being
accessed from userspace.  Page faulting is used to evict and remap
different regions of whichever buffers are being accessed from user-
space.

Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>