From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 28 Jul 2010 19:50:20 +0200 Subject: [PATCH 1/2] arm: msm: Add System MMU support. In-Reply-To: References: <1280270466-13503-1-git-send-email-stepanm@codeaurora.org> <201007281039.44883.arnd@arndb.de> Message-ID: <201007281950.20847.arnd@arndb.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wednesday 28 July 2010, stepanm at codeaurora.org wrote: > > On Wednesday 28 July 2010 00:41:06 Stepan Moskovchenko wrote: > >> Add support for the System MMUs found on the 8x60 and 8x72 > >> families of Qualcomm chips. These SMMUs allow virtualization > >> of the address space used by most of the multimedia cores > >> on these chips. > > > > How is this different from an IOMMU? > > > > From a very brief look, it seems that you should be using the > > existing dma-mapping APIs here instead of making up your own. > > > > Arnd > > > These are just SMMU APIs, and the DMA-mapping API is one layer above this. > > We have our own SMMU API for the MSM SoCs because we have muliple IOMMUs, > each one having multiple contexts, or even having multiple instances of > the same context. Our usage model is also quite a bit different from how > the DMA APIs are set up. I believe only two IOMMU drivers actually make > use of the DMA API (Intel and AMD) and the other ones (OMAP and other > SoCs) have their own APIs for their specific use cases. The DMA API is extremely flexible, it works just fine with all the IOMMUs that I've seen so far. Please take a look at include/asm-generic/dma-mapping-common.h and its users to see how to use multiple IOMMUs depending on the device. If the OMAP developers got this wrong, that's not your problem :-) Arnd