Den 14.09.2018 18.13, skrev Daniel Vetter:
On Fri, Sep 14, 2018 at 5:48 PM, Thomas Hellstrom <thomas@xxxxxxxxxxxx> wrote:
Hi, Noralf,
On 09/11/2018 02:43 PM, Noralf Trønnes wrote:
This patchset adds a library for shmem backed GEM objects and makes use
of it in tinydrm.
When I made tinydrm I used the CMA helper because it was very easy to
use. July last year I learned that this limits which drivers to PRIME
import from, since CMA requires continuous memory. tinydrm drivers don't
require that. So I set out to change that looking first at shmem, but
that wasn't working since shmem didn't work with fbdev deferred I/O.
Then I did a vmalloc buffer attempt which worked with deferred I/O, but
maybe wouldn't be of so much use as a library for other drivers to use.
As my work to split out stuff from the CMA helper for shared use came to
an end, I had a generic fbdev emulation that uses a shadow buffer for
deferred I/O.
This means that I can now use shmem buffers after all.
I have looked at the other drivers that use drm_gem_get_pages() and
several supports different cache modes so I've done that even though
tinydrm only uses the cached one.
Out if interest, how can you use writecombine and uncached with shared
memory?
as typically the linear kernel map of the affected pages also needs
changing?
I think on x86 at least the core code takes care of that. On arm, I'm
not sure this just works, since you can't change the mode of the
linear map. Instead you need specially allocated memory which is _not_
in the linear map. I guess arm boxes with pcie slots aren't that
common yet :-)
I was hoping to get some feedback on these cache mode flags.
These drivers use them:
udl/udl_gem.c
omapdrm/omap_gem.c
msm/msm_gem.c
etnaviv/etnaviv_gem.c
I don't know if they make sense or not, so any help is appreciated.
Noralf.
-Daniel
Thanks,
Thomas
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