From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rob Clark <robdclark@gmail.com>
Date: Mon, 27 May 2013 15:47:54 +0000
Subject: Re: Introduce a new helper framework for buffer synchronization
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To: Inki Dae <inki.dae@samsung.com>
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>, Daniel Vetter <daniel@ffwll.ch>, linux-fbdev <linux-fbdev@vger.kernel.org>, YoungJun Cho <yj44.cho@samsung.com>, Kyungmin Park <kyungmin.park@samsung.com>, "myungjoo.ham" <myungjoo.ham@samsung.com>, DRI mailing list <dri-devel@lists.freedesktop.org>, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org

On Mon, May 27, 2013 at 6:38 AM, Inki Dae <inki.dae@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 ba=
dly
> 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=3D=
dma-f
> ence-helper
>
> And fence helper codes,
>
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commi=
t/?
> h=3Ddma-fence-helper&id=ADcbc0fe7e285ce866e5816e5e21443dcce01005
>
> And example codes for device driver,
>
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/commi=
t/?
> h=3Ddma-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 someb=
ody
> 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
>