Introduce a new helper framework for buffer synchronization

[Rob Clark]

On Mon, May 27, 2013 at 6:38 AM, Inki Dae <inki.dae at samsung.com> wrote:
> Hi all,
>
> I have been removed previous branch and added new one with more cleanup.
> This time, the fence helper doesn't include user side interfaces and cache
> operation relevant codes anymore because not only we are not sure that
> coupling those two things, synchronizing caches and buffer access between
> CPU and CPU, CPU and DMA, and DMA and DMA with fences, in kernel side is a
> good idea yet but also existing codes for user side have problems with badly
> behaved or crashing userspace. So this could be more discussed later.
>
> The below is a new branch,
>
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/?h=dma-f
> ence-helper
>
> And fence helper codes,
>
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commit/?
> h=dma-fence-helper&id=adcbc0fe7e285ce866e5816e5e21443dcce01005
>
> And example codes for device driver,
>
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commit/?
> h=dma-fence-helper&id=d2ce7af23835789602a99d0ccef1f53cdd5caaae
>
> I think the time is not yet ripe for RFC posting: maybe existing dma fence
> and reservation need more review and addition work. So I'd glad for somebody
> giving other opinions and advices in advance before RFC posting.

thoughts from a *really* quick, pre-coffee, first look:
* any sort of helper to simplify single-buffer sort of use-cases (v4l)
probably wouldn't want to bake in assumption that seqno_fence is used.
* I guess g2d is probably not actually a simple use case, since I
expect you can submit blits involving multiple buffers :-P
* otherwise, you probably don't want to depend on dmabuf, which is why
reservation/fence is split out the way it is..  you want to be able to
use a single reservation/fence mechanism within your driver without
having to care about which buffers are exported to dmabuf's and which
are not.  Creating a dmabuf for every GEM bo is too heavyweight.

I'm not entirely sure if reservation/fence could/should be made any
simpler for multi-buffer users.  Probably the best thing to do is just
get reservation/fence rolled out in a few drivers and see if some
common patterns emerge.

BR,
-R

>
> Thanks,
> Inki Dae
>