Re: [PATCH 5/5] drm/vgem: properly implement mmap

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Feb 08, 2012 at 11:36:22PM +0000, Chris Wilson wrote:
> On Thu,  9 Feb 2012 00:19:31 +0100, Ben Widawsky <ben@bwidawsk.net> wrote:
> > Mostly copied from i915 gtt mmaps, this will properly fault in pages as
> > the user tries to use them. The only thing of note are that no
> > prefaulting occurs, so perhaps some kind of madvise will happen later if
> > needed.
> 
> What's the goal here? Why not copy the simpler (from the driver
> perspective) CPU mmaps? I presume that this will be required for dmabuf
> in some form?

Yeah, for proper instead of hacked-up dma_buf mmap support I expect that
the expoerter needs to provide some sort of vm_insert_pfn_from_dma_buf
function. We need this so that non-coherent dma_buf objects can fake
coherency and also to allow (eventually) eviction. For that the exporter
needs to be able to handle page-faults, so I've figured we might want to
hack something together.

I know it's not a beauty, because drm isn't a fs yet ;-)
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48