From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Date: Thu, 26 Aug 2010 09:17:25 +0000 Subject: Re: [RFC][PATCH] add Message-Id: <20100826091725.GC5355@pengutronix.de> List-Id: References: <201008201450.12585.mitov@issp.bas.bg> <20100826144000C.fujita.tomonori@lab.ntt.co.jp> <201008260904.19973.mitov@issp.bas.bg> <20100826152333K.fujita.tomonori@lab.ntt.co.jp> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: linux-arm-kernel@lists.infradead.org Hello, On Thu, Aug 26, 2010 at 11:06:20AM +0200, Guennadi Liakhovetski wrote: > On Thu, 26 Aug 2010, FUJITA Tomonori wrote: >=20 > > On Thu, 26 Aug 2010 09:04:14 +0300 > > Marin Mitov wrote: > >=20 > > > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote: > > > > On Fri, 20 Aug 2010 14:50:12 +0300 > > > > Marin Mitov wrote: > > > >=20 > > > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote: > > > > > > On Fri, 20 Aug 2010 11:13:45 +0300 > > > > > > Marin Mitov wrote: > > > > > >=20 > > > > > > > > > This tric is already used in drivers/staging/dt3155v4l.c > > > > > > > > > dt3155_alloc_coherent()/dt3155_free_coherent() > > > > > > > > >=20 > > > > > > > > > Here proposed for general use by popular demand from vide= o4linux folks. > > > > > > > > > Helps for videobuf-dma-contig framework. > > > > > > > >=20 > > > > > > > > What you guys exactly want to do? If you just want to pre-a= llocate > > > > > > > > coherent memory for latter usage, > > > > > > >=20 > > > > > > > Yes, just to preallocate not coherent, but rather contiguous = memory for latter usage. > > > > > > > We use coherent memory because it turns out to be contiguous. > > > > > >=20 > > > > > > Hmm, you don't care about coherency? You just need contiguous m= emory? > > > > >=20 > > > > > Yes. We just need contiguous memory. Coherency is important as fa= r as when dma > > > > > transfer finishes user land is able to see the new data. Could be= done by something like > > > > > dma_{,un}map_single() > > > >=20 > > > > 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. > > >=20 > > > Please, look at drivers/media/video/videobuf-dma-contig.c. Using cohe= rent memory > > > is inavoidable for now, there is no alternative for it for now. The t= wo new functions, > > > which I propose are just helpers for those of us who already use cohe= rent memory > > > (via videobuf-dma-contig API). May be adding these two functions to=20 > > > drivers/media/video/videobuf-dma-contig.c will be better solution? > >=20 > > If you add something to the videobuf-dma-contig API, that's fine by me > > because drivers/media/video/videobuf-dma-contig.c uses the own > > structure and plays with dma_alloc_coherent. As long as a driver > > doesn't touch device->dma_mem directly, it's fine, I think (that is, > > dt3155v4l driver is broken). There are already some workarounds for > > contigous memory in several drivers anyway. >=20 > No, this will not work - this API has to be used from board code and=20 > videobuf can be built modular. >=20 > > We will have the proper API for contiguous memory. I don't think that > > adding such workaround to the DMA API is a good idea. >=20 > We have currently a number of boards broken in the mainline. They must be= =20 > fixed for 2.6.36. I don't think the mentioned API will do this for us. So= ,=20 > as I suggested earlier, we need either this or my patch series >=20 > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595 this seems to be more mature to me. The original patch in this thread uses a symbol DT3155_COH_FLAGS which seems misplaced in generic code and doesn't put the new functions in a header. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig | Industrial Linux Solutions | http://www.pengutronix.de/ |