From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marek Szyprowski Subject: Re: [RFC 3/3] iommu: dma-iommu: use common implementation also on ARM architecture Date: Tue, 15 Mar 2016 13:03:04 +0100 Message-ID: <56E7F9F8.6030203@samsung.com> References: <1455870164-25337-1-git-send-email-m.szyprowski@samsung.com> <1455870164-25337-4-git-send-email-m.szyprowski@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-reply-to: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Magnus Damm Cc: linaro-mm-sig-cunTk1MwBs8s++Sfvej+rw@public.gmane.org, Krzysztof Kozlowski , Russell King - ARM Linux , Heiko Stuebner , Arnd Bergmann , Bartlomiej Zolnierkiewicz , Catalin Marinas , Will Deacon , linux-kernel , dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org, Inki Dae , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Sakari Ailus , Laurent Pinchart , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Mark Yao List-Id: iommu@lists.linux-foundation.org Hello, On 2016-03-15 12:18, Magnus Damm wrote: > Hi Marek, > > On Fri, Feb 19, 2016 at 5:22 PM, Marek Szyprowski > wrote: >> This patch replaces ARM-specific IOMMU-based DMA-mapping implementation >> with generic IOMMU DMA-mapping code shared with ARM64 architecture. The >> side-effect of this change is a switch from bitmap-based IO address space >> management to tree-based code. There should be no functional changes >> for drivers, which rely on initialization from generic arch_setup_dna_ops() >> interface. Code, which used old arm_iommu_* functions must be updated to >> new interface. >> >> Signed-off-by: Marek Szyprowski >> --- > Thanks for your efforts and my apologies for late comments. Just FYI > I'll try your patch (and this series) with the ipmmu-vmsa.c driver on > 32-bit ARM and see how it goes. Nice not to have to support multiple > interfaces depending on architecture! Thanks for testing! > One question that comes to mind is how to handle features. > > For instance, the 32-bit ARM code supports DMA_ATTR_FORCE_CONTIGUOUS > while the shared code in drivers/iommu/dma-iommu.c does not. I assume > existing users may rely on such features so from my point of view it > probably makes sense to carry over features from the 32-bit ARM code > into the shared code before pulling the plug. Right, this has to be added to common code before merging. > I also wonder if it is possible to do a step-by-step migration and > support both old and new interfaces in the same binary? That may make > things easier for multiplatform enablement. So far I've managed to > make one IOMMU driver support both 32-bit ARM and 64-bit ARM with some > ugly magic, so adjusting 32-bit ARM dma-mapping code to coexist with > the shared code in drivers/iommu/dma-iommu.c may also be possible. And > probably involving even more ugly magic. =) Having one IOMMU driver for both 32-bit and 64-bit ARM archs is quite easy IF you rely on the iommu core to setup everything. See exynos-iommu driver - after my last patches it now works fine on both archs (using arch specific interfaces). Most of the magic is done automatically by arch_setup_dma_ops(). The real problem is the fact that there are drivers (like DRM) which rely on specific dma-mapping functions from ARM architecture, which need to be rewritten. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland