[RFCv2 PATCH 7/9] v4l: vb2-dma-contig: change map/unmap behaviour

[Daniel Vetter]

On Thu, Mar 22, 2012 at 13:15, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
> On Tuesday 13 March 2012 11:17:05 Tomasz Stanislawski wrote:
>> The DMABUF documentation says that the map_dma_buf callback should return
>> scatterlist that is mapped into a caller's address space. In practice,
>> almost none of existing implementations of DMABUF exporter does it.  This
>> patch breaks the DMABUF specification in order to allow exchange DMABUF
>> buffers between other APIs like DRM.
>
> Then it's time to fix the spec, and squash 6/9 and 7/9 together (I started
> reviewing 6/9 and the implementation puzzled me until I saw the "fixes" in
> 7/9).

Nope. The drm proof of concept stuff that just grabbed the struct
pages pointers from the sg_table has always just been a gross hack to
get things of the ground. With proper kernel cpu access and mmap
support we can ditch these, and Dave Airlie has already started with
that:

http://cgit.freedesktop.org/~airlied/linux/log/?h=drm-dmabuf2

Furthermore the kernel cpu access helpers are designed to just plug
into the corresponding ttm helpers. It'll be slightly more messy for
drm/i915 and udl because they don't use ttm.

And the afaik the proof of concept stuff from Rob Clark very much
depends upon handing out addresses in the targets device address
space. And there are other scenarios that just require this, besides
that it makes imo more sense from an api design pov.

Yours, Daniel
-- 
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 365 57 48 - http://blog.ffwll.ch