[PATCH v4 00/19] Share TTM code among DRM framebuffer drivers

Gerd Hoffmann
Mon, 06 May 2019 14:20:34 -0000

On Mon, May 06, 2019 at 03:09:20PM +0200, Thomas Zimmermann
wrote:
> Hi
>
> Am 06.05.19 um 14:22 schrieb Gerd Hoffmann:
> >> GEM VRAM could implement PRIME helpers, which would allow for
using
> >> the generic fbcon.
> >
> > bochs_gem_prime_*() functions with this series applied look like you
can
> > just rename them & move over to vram helpers.
> >
> > It's not a full prime implementation, specifically actual
export/import
> > isn't there.  But pin+vmap (needed by generic fbcon) is
implemented.
>
> I did have a patch to do this, but then I read that prime requires DMA
> for buffer sharing and bochs works only because it's emulated.

For actual buffer sharing with other drivers yes because dma-bufs
typically are a bunch of pages (struct page**) and live in RAM.

Not sure whenever it is possible or useful to place the vram in
ZONE_DEVICE to get page structs for it, then export buffers located
in vram that way without copying them over to main memory.  I suspect
most importers would fail to properly setup PCI-PCI dma in that case.

> If bochs' implementation is complete enough to be useful for other
> drivers, I'll add it to the patch set.

It's good enough for generic fbcon.

cheers,
  Gerd