Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753605Ab0HZJGQ (ORCPT ); Thu, 26 Aug 2010 05:06:16 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:54837 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1753396Ab0HZJGO (ORCPT ); Thu, 26 Aug 2010 05:06:14 -0400 X-Authenticated: #20450766 X-Provags-ID: V01U2FsdGVkX1+y1vRMfj6ytkvP6jxWUJ9bsiIWus0EYu4x41WOK3 lLAOhInxTjtkWh Date: Thu, 26 Aug 2010 11:06:20 +0200 (CEST) From: Guennadi Liakhovetski To: FUJITA Tomonori cc: mitov@issp.bas.bg, linux-kernel@vger.kernel.org, Linux Media Mailing List , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org, =?ISO-8859-15?Q?Uwe_Kleine-K=F6nig?= , =?ISO-8859-15?Q?Philippe_R=E9tornaz?= , Greg Kroah-Hartman , Janusz Krzysztofik Subject: Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API In-Reply-To: <20100826152333K.fujita.tomonori@lab.ntt.co.jp> Message-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> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3310 Lines: 73 On Thu, 26 Aug 2010, FUJITA Tomonori wrote: > On Thu, 26 Aug 2010 09:04:14 +0300 > Marin Mitov wrote: > > > On Thursday, August 26, 2010 08:40:47 am FUJITA Tomonori wrote: > > > On Fri, 20 Aug 2010 14:50:12 +0300 > > > Marin Mitov wrote: > > > > > > > On Friday, August 20, 2010 11:35:06 am FUJITA Tomonori wrote: > > > > > On Fri, 20 Aug 2010 11:13:45 +0300 > > > > > Marin Mitov 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? > > 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. No, this will not work - this API has to be used from board code and videobuf can be built modular. > 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. We have currently a number of boards broken in the mainline. They must be fixed for 2.6.36. I don't think the mentioned API will do this for us. So, as I suggested earlier, we need either this or my patch series http://thread.gmane.org/gmane.linux.ports.sh.devel/8595 for 2.6.36. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- 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/