[PATCH v4 00/17] drm: add gem ttm helpers, rework mmap workflow.

[Gerd Hoffmann]

On Mon, Aug 26, 2019 at 10:47:07AM +0200, Thomas Zimmermann wrote:
> Hi,
> 
> I would have liked to get some context on the purpose of GEM TTM
> helpers. Is is just share-able code?

Yes.  Shareable code for drivers which use both ttm and gem (all except
vmgfx).

> From my understanding VRAM helpers _are_ GEM TTM helpers. And they where
> re-named to VRAM helpers, so that the naming is independent from the
> implementation (and vice versa).

I think vram helpers are for old/simple devices which basically support
dumb gem objects stored in vram (device memory typically exposed as pci
bar).  Using ttm underneath is largely an implementation detail for the
users of the vram helpers, they don't need to know.

> Wrt qxl, would it be possible to convert the driver over to VRAM helpers
> entirely? I noticed a memory region named PRIV. Could we add this to
> VRAM helpers?

PRIV is vram too, qxl has two pci bars with memory.  Historical reasons.
There are rules which pci bar can store which kind of objects.  I don't
think it makes sense to move such device-specific things into vram
helpers.  Also qxl is complex enough that you can hardly hide ttm behind
vram helpers.

cheers,
  Gerd