From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Date: Thu, 26 Aug 2010 09:53:11 +0000 Subject: Re: [RFC][PATCH] add Message-Id: <20100826095311.GA13051@pengutronix.de> List-Id: References: <201008260904.19973.mitov@issp.bas.bg> <20100826152333K.fujita.tomonori@lab.ntt.co.jp> <20100826182915S.fujita.tomonori@lab.ntt.co.jp> In-Reply-To: <20100826182915S.fujita.tomonori@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable To: linux-arm-kernel@lists.infradead.org On Thu, Aug 26, 2010 at 06:30:02PM +0900, FUJITA Tomonori wrote: > On Thu, 26 Aug 2010 11:06:20 +0200 (CEST) > Guennadi Liakhovetski wrote: >=20 > > 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 vi= deo4linux folks. > > > > > > > > > > Helps for videobuf-dma-contig framework. > > > > > > > > >=20 > > > > > > > > > What you guys exactly want to do? If you just want to pre= -allocate > > > > > > > > > coherent memory for latter usage, > > > > > > > >=20 > > > > > > > > Yes, just to preallocate not coherent, but rather contiguou= s memory for latter usage. > > > > > > > > We use coherent memory because it turns out to be contiguou= s. > > > > > > >=20 > > > > > > > Hmm, you don't care about coherency? You just need contiguous= memory? > > > > > >=20 > > > > > > 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() > > > > >=20 > > > > > Then, we should avoid using coherent memory as I exaplained befor= e. 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 co= herent 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 co= herent 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 > >=20 > > for 2.6.36. >=20 > Why can't you revert a commit that causes the regression? >=20 > The related DMA API wasn't changed in 2.6.36-rc1. The DMA API is not > responsible for the regression. And the patchset even exnteds the > definition of the DMA API (dma_declare_coherent_memory). Such change > shouldn't applied after rc1. I think that DMA-API.txt says that > dma_declare_coherent_memory() handles coherent memory for a particular > device. It's not for the API that reserves coherent memory that can be > used for any device for a single device. The patch that made the problem obvious for ARM is 309caa9cc6ff39d261264ec4ff10e29489afc8f8 aka v2.6.36-rc1~591^2~2^4~12. So this went in before v2.6.36-rc1. One of the "architectures which similar restrictions" is x86 BTW. And no, we won't revert 309caa9cc6ff39d261264ec4ff10e29489afc8f8 as it addresses a hardware restriction. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig | Industrial Linux Solutions | http://www.pengutronix.de/ |