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From devnull@lkml.org Tue Apr 23 21:05:13 2024 Delivery-date: Fri, 27 Aug 2010 09:06:00 +0200 Received: from mail.issp.bas.bg ([195.96.236.10]:59760 "EHLO mail.issp.bas.bg" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751392Ab0H0HF0 (ORCPT ); Fri, 27 Aug 2010 03:05:26 -0400 Received: from lfb.issp.bas.bg (IDENT:1000@lfb.issp.bas.bg [195.96.236.237]) by mail.issp.bas.bg (8.14.3/8.14.3) with ESMTP id o7R73URR002428; Fri, 27 Aug 2010 10:03:32 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=issp.bas.bg; s=default; t=1282892615; bh=nJQft+nhVfVR90GiW5fpafze064c39Lr5mZUsj0qFWQ=; h=From:To:Subject:Date:Cc:References:In-Reply-To:MIME-Version: Content-Type:Content-Transfer-Encoding:Message-Id; b=IxonlLkJd3ua From: Marin Mitov Organization: Institute of Solid State Physics To: FUJITA Tomonori Subject: Re: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API Date: Fri, 27 Aug 2010 10:02:20 +0300 User-Agent: KMail/1.13.3 (Linux/2.6.36-rc2; KDE/4.4.3; x86_64; ; ) Cc: u.kleine-koenig@pengutronix.de, g.liakhovetski@gmx.de, 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, philippe.retornaz@epfl.ch, gregkh@suse.de, jkrzys References: <20100827051907.GA17521@pengutronix.de> <201008270923.30297.mitov@issp.bas.bg> <20100827153204A.fujita.tomonori@lab.ntt.co.jp> In-Reply-To: <20100827153204A.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201008271002.29297.mitov@issp.bas.bg> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-Id: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, August 27, 2010 09:32:14 am FUJITA Tomonori wrote: > On Fri, 27 Aug 2010 09:23:21 +0300 > Marin Mitov wrote: > > > On Friday, August 27, 2010 08:57:59 am FUJITA Tomonori wrote: > > > On Fri, 27 Aug 2010 07:19:07 +0200 > > > Uwe Kleine-K$(D+S(Bnig wrote: > > > > > > > Hey, > > > > > > > > On Fri, Aug 27, 2010 at 02:00:17PM +0900, FUJITA Tomonori wrote: > > > > > On Fri, 27 Aug 2010 06:41:42 +0200 > > > > > Uwe Kleine-K$(D+S(Bnig wrote: > > > > > > On Thu, Aug 26, 2010 at 07:00:24PM +0900, FUJITA Tomonori wrote: > > > > > > > On Thu, 26 Aug 2010 11:53:11 +0200 > > > > > > > Uwe Kleine-K$(D+S(Bnig wrote: > > > > > > > > > > > > > > > > > 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. > > > > > > > > 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. > > > > > > > > > > > > > > How these drivers were able to work without hitting the hardware restriction? > > > > > > In my case the machine in question is an ARMv5, the hardware restriction > > > > > > is on ARMv6+ only. You could argue that so the breaking patch for arm > > > > > > should only break ARMv6, but I don't think this is sensible from a > > > > > > maintainers POV. We need an API that works independant of the machine > > > > > > that runs the code. > > > > > > > > > > Agreed. But insisting that the DMA API needs to be extended wrongly > > > > > after rc2 to fix the regression is not sensible too. The related DMA > > > > > API wasn't changed in 2.6.36-rc1. The API isn't responsible for the > > > > > regression at all. > > > > I think this isn't about "responsiblity". Someone in arm-land found > > > > that the way dma memory allocation worked for some time doesn't work > > > > anymore on new generation chips. As pointing out this problem was > > > > expected to find some matches it was merged in the merge window. One > > > > such match is the current usage of the DMA API that doesn't currently > > > > offer a way to do it right, so it needs a patch, no? > > > > > > No, I don't think so. We are talking about a regression, right? > > > > > > On new generation chips, something often doesn't work (which have > > > worked on old chips for some time). It's not a regresiion. I don't > > > think that it's sensible to make large change (especially after rc1) > > > to fix such issue. If you say that the DMA API doesn't work on new > > > chips and proposes a patch for the next merge window, it's sensible, I > > > suppose. > > > > > > Btw, the patch isn't a fix for the DMA API. It tries to extend the DMA > > > API (and IMO in the wrong way). > > > In addition, the patch might break the > > > current code. > > > > To "break the current code" is simply not possible. Sorry to oppose. As you have written it > > "extend the DMA API", so if you do not use the new API (and no current code is using it) > > you cannot "break the current code". > > Looks like that the patch adds the new API that touches the exisitng > code. It means the existing code could break. So the exsising API > could break too. > > http://thread.gmane.org/gmane.linux.ports.sh.devel/8595 > -- > To unsubscribe from this list: send the line "unsubscribe linux-media" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/