From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Date: Mon, 27 May 2013 15:23:00 +0000
Subject: Re: Introduce a new helper framework for buffer synchronization
Message-Id: <51A37A54.1040700@canonical.com>
List-Id: <linux-fbdev.vger.kernel.org>
References: <CAAQKjZP=iOmHRpHZCbZD3v_RKUFSn0eM_WVZZvhe7F9g3eTmPA@mail.gmail.com> <CAF6AEGuDih-NR-VZCmQfqbvCOxjxreZRPGfhCyL12FQ1Qd616Q@mail.gmail.com> <006a01ce504e$0de3b0e0$29ab12a0$%dae@samsung.com> <CAF6AEGv2FiKMUpb5s4zHPdj4uVxnQWdVJWL-i1mOOZRxBvMZ4Q@mail.gmail.com> <00cf01ce512b$bacc5540$3064ffc0$%dae@samsung.com> <CAF6AEGuBexKUpTwm9cjGjkxCTKgEaDhAakeP0RN=rtLS6Qy=Mg@mail.gmail.com> <CAAQKjZP37koEPob6yqpn-WxxTh3+O=twyvRzDiEhVJTD8BxQzw@mail.gmail.com> <20130520211304.GV12292@phenom.ffwll.local> <20130520213033.GW12292@phenom.ffwll.local> <032701ce55f1$3e9ba4b0$bbd2ee10$%dae@samsung.com> <20130521074441.GZ12292@phenom.ffwll.local> <033a01ce5604$c32bd250$498376f0$%dae@samsung.com> <CAKMK7uHtk+A7CDZH3qHt+F3H_fdSsWwt-bEPn-N0919oOE+Jkg@mail.gmail.com> <012801ce57ba$a5a87fa0$f0f97ee0$%dae@samsu
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To: Inki Dae <inki.dae@samsung.com>
Cc: 'Daniel Vetter' <daniel@ffwll.ch>, 'Rob Clark' <robdclark@gmail.com>, '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

Hey,

Op 27-05-13 12:38, Inki Dae schreef:
> 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,
> =09
> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/?h=3D=
dma-f
> ence-helper
>
> And fence helper codes,
> =09
> 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,
> =09
> 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.
>
NAK.

For examples for how to handle locking properly, see Documentation/ww-mutex=
-design.txt in my recent tree.
I could list what I believe is wrong with your implementation, but real pro=
blem is that the approach you're taking is wrong.

~Maarten