From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 32E3E6B02A8 for ; Tue, 13 Jul 2010 04:34:23 -0400 (EDT) Date: Tue, 13 Jul 2010 09:42:44 +0100 From: Alan Cox Subject: Re: [RFC 3/3] mm: iommu: The Virtual Contiguous Memory Manager Message-ID: <20100713094244.7eb84f1b@lxorguk.ukuu.org.uk> In-Reply-To: <20100713173028M.fujita.tomonori@lab.ntt.co.jp> References: <4C3BFDD3.8040209@codeaurora.org> <20100713145852C.fujita.tomonori@lab.ntt.co.jp> <20100713092012.7c1fe53e@lxorguk.ukuu.org.uk> <20100713173028M.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: FUJITA Tomonori Cc: zpfeffer@codeaurora.org, joro@8bytes.org, dwalker@codeaurora.org, andi@firstfloor.org, randy.dunlap@oracle.com, mel@csn.ul.ie, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-ID: On Tue, 13 Jul 2010 17:30:43 +0900 FUJITA Tomonori wrote: > On Tue, 13 Jul 2010 09:20:12 +0100 > Alan Cox wrote: > > > > Why video4linux can't use the DMA API? Doing DMA with vmalloc'ed > > > buffers is a thing that we should avoid (there are some exceptions > > > like xfs though). > > > > Vmalloc is about the only API for creating virtually linear memory areas. > > The video stuff really needs that to avoid lots of horrible special cases > > when doing buffer processing and the like. > > > > Pretty much each driver using it has a pair of functions 'rvmalloc' and > > 'rvfree' so given a proper "vmalloc_for_dma()" type interface can easily > > be switched > > We already have helper functions for DMA with vmap pages, > flush_kernel_vmap_range and invalidate_kernel_vmap_range. I'm not sure they help at all because the DMA user for these pages isn't the video driver - it's the USB layer, and the USB layer isn't specifically aware it is being passed vmap pages. Alan -- 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