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

Daniel Vetter
Mon, 06 May 2019 15:23:20 -0000

On Mon, May 06, 2019 at 04:20:34PM +0200, Gerd Hoffmann
wrote:
> 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.

Christian K?nig is working on p2p dma-buf sharing. Not sure that's worth
it for virtual devices, but could be fun to wire up I guess.
-Daniel

>
> > 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
>

--
Daniel Vetter
Software Engineer, Intel Corporation