drm: Why shmem?

[Noralf Trønnes]

Hi,

Currently I'm using the cma library with tinydrm because it was so
simple to use even though I have to work around the fact that reads are
uncached. A bigger problem that I have become aware of, is that it
restricts the dma buffers it can import since they have to be continous.

So I looked to udl and it uses shmem. Fine, let's make a shmem gem
library similar to the cma library.

Now I have done so and have started to think about the DOC: section,
explaining what the library does. And I'm stuck, what's the benefit of
using shmem compared to just using alloc_page()?

Noralf.