From: Rob Clark <robdclark@chromium.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
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<freedreno@lists.freedesktop.org>,
christian.koenig@amd.com
Subject: Re: [PATCH 0/6] drm+dma: cache support for arm, etc
Date: Mon, 19 Aug 2019 07:39:28 -0700 [thread overview]
Message-ID: <CAJs_Fx4YfU8iqN+t-h-HxsWRd-KAasHcQaV-9p4Wz=A--5Epew@mail.gmail.com> (raw)
In-Reply-To: <20190819052337.GA16622@lst.de>
On Sun, Aug 18, 2019 at 10:23 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Fri, Aug 16, 2019 at 02:04:35PM -0700, Rob Clark wrote:
> > I don't disagree about needing an API to get uncached memory (or
> > ideally just something outside of the linear map). But I think this
> > is a separate problem.
> >
> > What I was hoping for, for v5.4, is a way to stop abusing dma_map/sync
> > for cache ops to get rid of the hack I had to make for v5.3. And also
> > to fix vgem on non-x86. (Unfortunately changing vgem to used cached
> > mappings breaks x86 CI, but fixes CI on arm/arm64..) We can do that
> > without any changes in allocation. There is still the possibility for
> > problems due to cached alias, but that has been a problem this whole
> > time, it isn't something new.
>
> But that just means we start exposing random low-level APIs that
> people will quickly abuse.. In fact even your simple plan to some
> extent already is an abuse of the intent of these functions, and
> it also requires a lot of knowledge in the driver that in the normal
> cases drivers can't know (e.g. is the device dma coherent or not).
I can agree that most drivers should use the higher level APIs.. but
not that we must prevent *all* drivers from using them. Most of what
DMA API is trying to solve doesn't apply to a driver like drm/msm..
which is how we ended up with hacks to try and misuse the high level
API to accomplish what we need.
Perhaps we can protect the prototypes with #ifdef LOWLEVEL_DMA_API /
#endif type thing to make it more obvious to other drivers that it
probably isn't the API they should use?
BR,
-R
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next prev parent reply other threads:[~2019-08-19 14:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-14 21:59 [PATCH 0/6] drm+dma: cache support for arm, etc Rob Clark
2019-08-14 21:59 ` [PATCH 1/6] arm64: export arch_sync_dma_for_*() Rob Clark
2019-08-14 21:59 ` [PATCH 2/6] mips: " Rob Clark
2019-08-14 21:59 ` [PATCH 4/6] arm: add arch_sync_dma_for_*() Rob Clark
2019-08-15 6:51 ` [PATCH 0/6] drm+dma: cache support for arm, etc Christoph Hellwig
2019-08-15 13:54 ` Rob Clark
2019-08-15 17:53 ` Christoph Hellwig
2019-08-15 18:21 ` Koenig, Christian
2019-08-15 18:27 ` Christoph Hellwig
2019-08-16 21:04 ` Rob Clark
2019-08-19 5:23 ` Christoph Hellwig
2019-08-19 14:39 ` Rob Clark [this message]
[not found] <215e5cb7-0fcf-48db-a656-817054dde420@email.android.com>
2019-08-15 18:52 ` Christoph Hellwig
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