Hello, On 2016-03-15 12:18, Magnus Damm wrote: > Hi Marek, > > On Fri, Feb 19, 2016 at 5:22 PM, Marek Szyprowski > <m.szyprowski at samsung.com> 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 <m.szyprowski at samsung.com> >> --- > 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
