[Ce-android-mainline] [RFC][PATCH 1/1] gpu: ion: Add IOMMU heap allocator with IOMMU API

[Hiroshi Doyu]

From: Hiroshi Doyu <hdoyu at nvidia.com>
Subject: Re: [Ce-android-mainline] [RFC][PATCH 1/1] gpu: ion: Add IOMMU heap allocator with IOMMU API
Date: Thu, 19 Jan 2012 16:15:38 +0200 (EET)
Message-ID: <20120119.161538.1686847422348460522.hdoyu at nvidia.com>

> Hi Arnd,
> 
> Thank you for your reivew. Some questions are inlined.
> 
> From: Arnd Bergmann <arnd at arndb.de>
> Subject: Re: [Ce-android-mainline] [RFC][PATCH 1/1] gpu: ion: Add IOMMU heap allocator with IOMMU API
> Date: Thu, 19 Jan 2012 13:04:34 +0100
> Message-ID: <201201191204.35067.arnd at arndb.de>
> 
> > On Wednesday 18 January 2012, Hiroshi Doyu wrote:
> > > Hi,
> > >
> > > Recently we've implemented IOMMU heap as an attachment which is one of
> > > the ION memory manager(*1) heap/backend. This implementation is
> > > completely independent of any SoC, and this can be used for other SoC
> > > as well. If our implementation is not totally wrong, it would be nice
> > > to share some experience/code here since Ion is still not so clear to
> > > me yet.
> > >
> > > I found that Linaro also seems to have started some ION work(*2). I
> > > think that some of Ion feature could be supported/replaced with Linaro
> > > UMM. For example, presently "ion_iommu_heap" is implemented with the
> > > standard IOMMU API, but it could be also implemented with the coming
> > > DMA API? Also DMABUF can be used in Ion core part as well, I guess.
> > >
> > > Currently there's no Ion memmgr code in the upstream
> > > "drivers/staging/android"(*3). Is there any plan to support this? Or
> > > is this something considered as a completely _temporary_ solution, and
> > > never going to be added?
> > >
> > > It would be nice if we can share some of our effort here since not
> > > small Android users need Ion, even temporary.
> > >
> > > Any comment would be really appreciated.
> >
> > Hi,
> >
> > Your implemention looks quite nice overall, but on the high level,
> > I don't see what the benefit of using the IOMMU API is here instead
> > of the dma-mapping API. I believe that all device drivers should
> > by default use the dma-mapping interfaces, which may in turn
> > be based on linear mapping (possibly using CMA) or an IOMMU.
> 
> Using dma-mapping API could be left for v2 of this patch.

FYI:

I've updated the patch with DMA API(v5). This is just kind of
proot-of-concept that Ion can do mapping with DMA API. This patch may
be changed a lot if DMABUF is introduced into Ion.
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