From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 7F27B6B004A for ; Mon, 11 Jul 2011 15:05:52 -0400 (EDT) From: Janusz Krzysztofik Subject: Re: [Linaro-mm-sig] [PATCH 6/8] drivers: add Contiguous Memory Allocator Date: Mon, 11 Jul 2011 21:01:17 +0200 References: <1309851710-3828-1-git-send-email-m.szyprowski@samsung.com> <201107091657.07925.jkrzyszt@tis.icnet.pl> <001e01cc3fd1$159f7bf0$40de73d0$%szyprowski@samsung.com> In-Reply-To: <001e01cc3fd1$159f7bf0$40de73d0$%szyprowski@samsung.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <201107112101.18601.jkrzyszt@tis.icnet.pl> Sender: owner-linux-mm@kvack.org List-ID: To: Marek Szyprowski Cc: 'Arnd Bergmann' , 'Marin Mitov' , 'Daniel Walker' , 'Russell King - ARM Linux' , 'Jonathan Corbet' , 'Mel Gorman' , 'Chunsang Jeong' , 'KAMEZAWA Hiroyuki' , linux-kernel@vger.kernel.org, 'Michal Nazarewicz' , 'Guennadi Liakhovetski' , linaro-mm-sig@lists.linaro.org, 'Jesse Barker' , 'Kyungmin Park' , 'Ankita Garg' , 'FUJITA Tomonori' , 'Andrew Morton' , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org Dnia poniedzia=C5=82ek, 11 lipca 2011 o 15:47:32 Marek Szyprowski napisa=C5= =82(a): > Hello, >=20 > On Saturday, July 09, 2011 4:57 PM Janusz Krzysztofik wrote: > > On Wed, 6 Jul 2011 at 16:59:45 Arnd Bergmann wrote: > > > On Wednesday 06 July 2011, Nicolas Pitre wrote: > > > > On Wed, 6 Jul 2011, Russell King - ARM Linux wrote: > > > > > Another issue is that when a platform has restricted DMA > > > > > regions, they typically don't fall into the highmem zone.=20 > > > > > As the dmabounce code allocates from the DMA coherent > > > > > allocator to provide it with guaranteed DMA-able memory, > > > > > that would be rather inconvenient. > > > >=20 > > > > Do we encounter this in practice i.e. do those platforms > > > > requiring large contiguous allocations motivating this work > > > > have such DMA restrictions? > > >=20 > > > You can probably find one or two of those, but we don't have to > > > optimize for that case. I would at least expect the maximum size > > > of the allocation to be smaller than the DMA limit for these, > > > and consequently mandate that they define a sufficiently large > > > CONSISTENT_DMA_SIZE for the crazy devices, or possibly add a > > > hack to unmap some low memory and call > > > dma_declare_coherent_memory() for the device. > >=20 > > Once found that Russell has dropped his "ARM: DMA: steal memory for > > DMA coherent mappings" for now, let me get back to this idea of a > > hack that would allow for safely calling > > dma_declare_coherent_memory() in order to assign a device with a > > block of contiguous memory for exclusive use. >=20 > We tested such approach and finally with 3.0-rc1 it works fine. You > can find an example for dma_declare_coherent() together with > required memblock_remove() calls in the following patch series: > http://www.spinics.net/lists/linux-samsung-soc/msg05026.html > "[PATCH 0/3 v2] ARM: S5P: Add support for MFC device on S5PV210 and > EXYNOS4" >=20 > > Assuming there should be no problem with successfully allocating a > > large continuous block of coherent memory at boot time with > > dma_alloc_coherent(), this block could be reserved for the device. > > The only problem is with the dma_declare_coherent_memory() calling > > ioremap(), which was designed with a device's dedicated physical > > memory in mind, but shouldn't be called on a memory already > > mapped. >=20 > All these issues with ioremap has been finally resolved in 3.0-rc1. > Like Russell pointed me in > http://www.spinics.net/lists/arm-kernel/msg127644.html, ioremap can > be fixed to work on early reserved memory areas by selecting > ARCH_HAS_HOLES_MEMORYMODEL Kconfig option. I'm not sure. Recently I tried to refresh my now 7 months old patch in=20 which I used that 'memblock_remove() then dma_declare_coherent_memery()'=20 method[1]. It was different from your S5P MFC example in that it didn't=20 punch any holes in the system memory, only stole a block of SDRAM from=20 its tail. But Russell reminded me again: "we should not be mapping SDRAM=20 using device mappings."[2]. Would defining ARCH_HAS_HOLES_MEMORYMODEL=20 (even if it was justified) make any diference in my case? I don't think=20 so. Wnat I think, after Russell, is that we still need that obligatory=20 ioremap() removed from dma_declare_coherent_memory(), or made it=20 optional, or a separate dma_declare_coherent_memory()-like function=20 without (obligatory) ioremap() provided by the DMA API, in order to get=20 the dma_declare_coherent_memery() method being accepted without any=20 reservations when used inside arch/arm, I'm afraid. Thanks, Janusz [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2010-December/034= 644.html [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2011-June/052488.= html -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org