linux-kernel - Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved

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Date:	Sun, 10 Oct 2010 23:08:22 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mitov@...p.bas.bg
Cc:	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, g.liakhovetski@....de
Subject: Re: [RFC][PATCH] add
 dma_reserve_coherent_memory()/dma_free_reserved_memory() API

On Fri, 20 Aug 2010 14:50:12 +0300
Marin Mitov <mitov@...p.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@...p.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.

The approach enables us to solve this issue without adding any new
API.
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