Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751819Ab0HZJcK (ORCPT ); Thu, 26 Aug 2010 05:32:10 -0400 Received: from sh.osrg.net ([192.16.179.4]:39731 "EHLO sh.osrg.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750803Ab0HZJcI (ORCPT ); Thu, 26 Aug 2010 05:32:08 -0400 Date: Thu, 26 Aug 2010 18:30:02 +0900 To: g.liakhovetski@gmx.de Cc: fujita.tomonori@lab.ntt.co.jp, mitov@issp.bas.bg, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org, u.kleine-koenig@pengutronix.de, philippe.retornaz@epfl.ch, gregkh@suse.de, jkrzyszt@tis.icnet.pl Subject: Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API From: FUJITA Tomonori In-Reply-To: References: <201008260904.19973.mitov@issp.bas.bg> <20100826152333K.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <20100826182915S.fujita.tomonori@lab.ntt.co.jp> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.0 (sh.osrg.net [192.16.179.4]); Thu, 26 Aug 2010 18:30:04 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3917 Lines: 74 On Thu, 26 Aug 2010 11:06:20 +0200 (CEST) Guennadi Liakhovetski wrote: > 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. Why can't you revert a commit that causes the regression? 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. -- 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/