Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

Marin Mitov
2010-10-13T16:43:34Z

On Wednesday, October 13, 2010 11:04:57 am KAMEZAWA Hiroyuki wrote:
> On Sun, 10 Oct 2010 23:08:22 +0900
> FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp> wrote:
>
> > On Fri, 20 Aug 2010 14:50:12 +0300
> > Marin Mitov <mitov@issp.bas.bg> wrote:
> >
> > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote:
> > > > On Fri, 20 Aug 2010 11:13:45 +0300
> > > > Marin Mitov <mitov@issp.bas.bg> wrote:
> > > >
> > > > > > > This tric is already used in drivers/staging/dt3155v4l.c
> > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent()
> > > > > > >
> > > > > > > Here proposed for general use by popular demand from video4linux folks.
> > > > > > > Helps for videobuf-dma-contig framework.
> > > > > >
> > > > > > What you guys exactly want to do? If you just want to pre-allocate
> > > > > > coherent memory for latter usage,
> > > > >
> > > > > Yes, just to preallocate not coherent, but rather contiguous memory for latter usage.
> > > > > We use coherent memory because it turns out to be contiguous.
> > > >
> > > > Hmm, you don't care about coherency? You just need contiguous memory?
> > >
> > > Yes. We just need contiguous memory. Coherency is important as far as when dma
> > > transfer finishes user land is able to see the new data. Could be done by something like
> > > dma_{,un}map_single()
> >
> > Anyone is working on this?
> >
> > KAMEZAWA posted a patch to improve the generic page allocator to
> > allocate physically contiguous memory. He said that he can push it
> > into mainline.
> >
> I said I do make an effort ;)
> New one here.
>
> http://lkml.org/lkml/2010/10/12/421

I like the patch. The possibility to allocate a contiguous chunk of memory
(or few of them) is what I need. The next step will be to get a dma handle
(for dma transfers to/from) and then mmap them to user space.

Thanks.

Marin Mitov

>
> Thanks,
> -Kame
>