From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:33753) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S1xu8-0007zT-N3 for qemu-devel@nongnu.org; Mon, 27 Feb 2012 05:34:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S1xu1-0007mo-9s for qemu-devel@nongnu.org; Mon, 27 Feb 2012 05:34:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34702) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S1xu1-0007mh-1i for qemu-devel@nongnu.org; Mon, 27 Feb 2012 05:33:57 -0500 Date: Mon, 27 Feb 2012 12:33:49 +0200 From: "Michael S. Tsirkin" Message-ID: <20120227103349.GB6731@redhat.com> References: <1330054063-16860-1-git-send-email-david@gibson.dropbear.id.au> <1330054063-16860-5-git-send-email-david@gibson.dropbear.id.au> <20120226100449.GB11324@redhat.com> <20120227002243.GE3433@truffala.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120227002243.GE3433@truffala.fritz.box> Subject: Re: [Qemu-devel] [PATCH 4/8] Add universal DMA helper functions List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: anthony@codemonkey.ws, qemu-devel@nongnu.org, Joerg Rodel , Eduard - Gabriel Munteanu , Richard Henderson On Mon, Feb 27, 2012 at 11:22:43AM +1100, David Gibson wrote: > On Sun, Feb 26, 2012 at 12:04:49PM +0200, Michael S. Tsirkin wrote: > > On Fri, Feb 24, 2012 at 02:27:39PM +1100, David Gibson wrote: > > > Not that long ago, every device implementation using DMA directly > > > accessed guest memory using cpu_physical_memory_*(). This meant that > > > adding support for a guest visible IOMMU would require changing every > > > one of these devices to go through IOMMU translation. > > > > > > Shortly before qemu 1.0, I made a start on fixing this by providing > > > helper functions for PCI DMA. These are currently just stubs which > > > call the direct access functions, but mean that an IOMMU can be > > > implemented in one place, rather than for every PCI device. > > > > > > Clearly, this doesn't help for non PCI devices, which could also be > > > IOMMU translated on some platforms. It is also problematic for the > > > devices which have both PCI and non-PCI version (e.g. OHCI, AHCI) - we > > > cannot use the the pci_dma_*() functions, because they assume the > > > presence of a PCIDevice, but we don't want to have to check between > > > pci_dma_*() and cpu_physical_memory_*() every time we do a DMA in the > > > device code. > > > > > > This patch makes the first step on addressing both these problems, by > > > introducing new (stub) dma helper functions which can be used for any > > > DMA capable device. > > > > > > These dma functions take a DMAContext *, a new (currently empty) > > > variable describing the DMA address space in which the operation is to > > > take place. NULL indicates untranslated DMA directly into guest > > > physical address space. The intention is that in future non-NULL > > > values will given information about any necessary IOMMU translation. > > > > > > DMA using devices must obtain a DMAContext (or, potentially, contexts) > > > from their bus or platform. For now this patch just converts the PCI > > > wrappers to be implemented in terms of the universal wrappers, > > > converting other drivers can take place over time. > > > > > > Cc: Michael S. Tsirkin > > > Cc: Joerg Rodel > > > Cc: Eduard - Gabriel Munteanu > > > Cc: Richard Henderson > > > > > > Signed-off-by: David Gibson > > > > I'm a bit confused with all the stubbing going on. > > Is this the final form of the pci_* functions or just > > a stub? If the final form, we probably should just > > open-code them - they don't buy us much. > > If not, let's add a comment? > > Well.. it's the intended final form of pci_dma_*() - which do become > trivial wrappers, yes. I'd say let's drop them then (in a follow-up patch). The topic is confusing enough without having to wade through layers of wrappers :) > It's _not_ the intended final form of dma_*(), > which need to grow code to do actual IOMMU translation. I'll add a > comment about this in the next round. > > -- > David Gibson | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ > | _way_ _around_! > http://www.ozlabs.org/~dgibson