From: Marin Mitov <mitov@issp.bas.bg>
Organization: Institute of Solid State Physics
To: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Subject: Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API
Date: Thu, 26 Aug 2010 09:04:14 +0300
User-Agent: KMail/1.13.3 (Linux/2.6.36-rc2; KDE/4.4.3; x86_64; ; )
Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        akpm@linux-foundation.org
References: <201008201113.46036.mitov@issp.bas.bg> <201008201450.12585.mitov@issp.bas.bg> <20100826144000C.fujita.tomonori@lab.ntt.co.jp>
In-Reply-To: <20100826144000C.fujita.tomonori@lab.ntt.co.jp>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <201008260904.19973.mitov@issp.bas.bg>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2165
Lines: 51

On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori 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()
> 
> Then, we should avoid using coherent memory as I exaplained before. In
> addition, dma_alloc_coherent can't provide large enough contigous
> memory for some drivers so this patch doesn't help much.

Please, look at drivers/media/video/videobuf-dma-contig.c. Using coherent memory
is inavoidable for now, there is no alternative for it for now. The two new functions,
which I propose are just helpers for those of us who already use coherent memory
(via videobuf-dma-contig API). May be adding these two functions to 
drivers/media/video/videobuf-dma-contig.c will be better solution?

Thanks.

Marin Mitov

> 
> We need the proper API for contiguous memory. Seem that we could have
> something:
> 
> http://lkml.org/lkml/2010/8/20/167
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/