From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id D9CD26B024D for ; Tue, 20 Jul 2010 06:10:58 -0400 (EDT) Date: Tue, 20 Jul 2010 19:09:31 +0900 Subject: Re: [RFC 1/3 v3] mm: iommu: An API to unify IOMMU, CPU and device memory management From: FUJITA Tomonori In-Reply-To: <20100719082213.GA7421@n2100.arm.linux.org.uk> References: <20100715080710T.fujita.tomonori@lab.ntt.co.jp> <20100715014148.GC2239@codeaurora.org> <20100719082213.GA7421@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <20100720190904N.fujita.tomonori@lab.ntt.co.jp> Sender: owner-linux-mm@kvack.org To: linux@arm.linux.org.uk Cc: zpfeffer@codeaurora.org, fujita.tomonori@lab.ntt.co.jp, ebiederm@xmission.com, linux-arch@vger.kernel.org, dwalker@codeaurora.org, mel@csn.ul.ie, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, andi@firstfloor.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-ID: On Mon, 19 Jul 2010 09:22:13 +0100 Russell King - ARM Linux wrote: > > If I want to share the buffer with another device I have to > > make a copy of the entire thing then fix up the virtual mappings for > > the other device I'm sharing with. > > This is something the DMA API doesn't do - probably because there hasn't > been a requirement for it. > > One of the issues for drivers is that by separating the mapped scatterlist > from the input buffer scatterlist, it creates something else for them to > allocate, which causes an additional failure point - and as all users sit > well with the current API, there's little reason to change especially > given the number of drivers which would need to be updated. Agreed. There was the discussion about separating 'dma_addr and dma_len' from scatterlist struct but I don't think that it's worth doing so. > I'm just proving that it's not as hard as you seem to be making out. Agreed again. -- 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/ . Don't email: email@kvack.org