Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966224AbbBCPTk (ORCPT ); Tue, 3 Feb 2015 10:19:40 -0500 Received: from mail-ig0-f172.google.com ([209.85.213.172]:45729 "EHLO mail-ig0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966208AbbBCPTd (ORCPT ); Tue, 3 Feb 2015 10:19:33 -0500 MIME-Version: 1.0 In-Reply-To: <20150203144109.GR8656@n2100.arm.linux.org.uk> References: <1422347154-15258-1-git-send-email-sumit.semwal@linaro.org> <20150203074856.GF14009@phenom.ffwll.local> <4689826.8DDCrX2ZhK@wuerfel> <20150203144109.GR8656@n2100.arm.linux.org.uk> Date: Tue, 3 Feb 2015 10:19:32 -0500 Message-ID: Subject: Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms From: Rob Clark To: Russell King - ARM Linux Cc: Arnd Bergmann , "linux-arm-kernel@lists.infradead.org" , Sumit Semwal , LKML , "linux-media@vger.kernel.org" , DRI mailing list , Linaro MM SIG Mailman List , "linux-mm@kvack.org" , Linaro Kernel Mailman List , Tomasz Stanislawski , Robin Murphy , Marek Szyprowski , Daniel Vetter Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1970 Lines: 41 On Tue, Feb 3, 2015 at 9:41 AM, Russell King - ARM Linux wrote: > On Tue, Feb 03, 2015 at 03:17:27PM +0100, Arnd Bergmann wrote: >> On Tuesday 03 February 2015 09:04:03 Rob Clark wrote: >> > Since I'm stuck w/ an iommu, instead of built in mmu, my plan was to >> > drop use of dma-mapping entirely (incl the current call to dma_map_sg, >> > which I just need until we can use drm_cflush on arm), and >> > attach/detach iommu domains directly to implement context switches. >> > At that point, dma_addr_t really has no sensible meaning for me. >> >> I think what you see here is a quite common hardware setup and we really >> lack the right abstraction for it at the moment. Everybody seems to >> work around it with a mix of the dma-mapping API and the iommu API. >> These are doing different things, and even though the dma-mapping API >> can be implemented on top of the iommu API, they are not really compatible. > > I'd go as far as saying that the "DMA API on top of IOMMU" is more > intended to be for a system IOMMU for the bus in question, rather > than a device-level IOMMU. > > If an IOMMU is part of a device, then the device should handle it > (maybe via an abstraction) and not via the DMA API. The DMA API should > be handing the bus addresses to the device driver which the device's > IOMMU would need to generate. (In other words, in this circumstance, > the DMA API shouldn't give you the device internal address.) if the dma_addr_t becomes the address upstream of the iommu (in practice, the phys addr), that would, I think, address my concerns about dma_addr_t BR, -R > -- > FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up > according to speedtest.net. -- 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/