Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753571Ab0HZKVv (ORCPT ); Thu, 26 Aug 2010 06:21:51 -0400 Received: from mail.issp.bas.bg ([195.96.236.10]:51871 "EHLO mail.issp.bas.bg" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753317Ab0HZKVt convert rfc822-to-8bit (ORCPT ); Thu, 26 Aug 2010 06:21:49 -0400 From: Marin Mitov Organization: Institute of Solid State Physics To: "Uwe =?iso-8859-1?q?Kleine-K=F6nig?=" Subject: Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API Date: Thu, 26 Aug 2010 13:18:22 +0300 User-Agent: KMail/1.13.3 (Linux/2.6.36-rc2; KDE/4.4.3; x86_64; ; ) Cc: Guennadi Liakhovetski , FUJITA Tomonori , linux-kernel@vger.kernel.org, Linux Media Mailing List , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org, Philippe =?iso-8859-1?q?R=E9tornaz?= , "Greg Kroah-Hartman" , Janusz Krzysztofik References: <201008201450.12585.mitov@issp.bas.bg> <20100826091725.GC5355@pengutronix.de> In-Reply-To: <20100826091725.GC5355@pengutronix.de> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT Message-Id: <201008261318.31784.mitov@issp.bas.bg> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3923 Lines: 84 On Thursday, August 26, 2010 12:17:25 pm Uwe Kleine-K?nig wrote: > Hello, > > On Thu, Aug 26, 2010 at 11:06:20AM +0200, 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 > 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. You are right. DT3155_COH_FLAGS should be defined, and a declaration should be put in the headers. But it is just RFC :-) Marin Mitov > > Best regards > Uwe > > -- 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/