On 14.10.2015 [08:42:51 -0700], Christoph Hellwig wrote: > Hi Nishanth, > > sorry for the late reply. > > > > On Power, since it's technically variable, we'd need a function. So are > > > you suggesting define'ing it to a function just on Power and leaving it > > > a constant elsewhere? > > > > > > I noticed that sparc has a IOMMU_PAGE_SHIFT already, fwiw. > > > > Sorry, I should have been more specific -- I'm ready to spin out a v3, > > with a sparc-specific function. > > > > Are you ok with leaving it a function for now (the only caller is in > > NVMe obviously). > > > I guess we do indeed need a function then. I'll take a look at your > patch, but as long you found a way to avoid adding too much boilerplate > code it should be fine. Ok, so I've got the moved function (include/linux/dma-mapping.h instead of dma-mapping-common.h) ready to go, which should only involve changing the first patch in the series. But I'm really mystified by what to do for sparc, which defines IOMMU_PAGE_SHIFT and IO_PAGE_SHIFT in arch/sparc/kernel/iommu_common.h. 1) Which constant reflects the value we mean for this function on sparc? I assume it should be IOMMU_PAGE_SHIFT, but they are the same value and I want to make sure I get the semantics right. 2) Where would I put sparc's definition of dma_get_page_shift()? Should it be in a asm/dma-mapping.h? Should we move some of the constants from arch/sparc/kernel/iommu_common.h to arch/sparc/include/asm/iommu_common.h and then #include that in asm/dma-mapping.h? Dave M., any opinions/insights? Essentially, this helper function assists the NVMe driver in determining what page size it should use to satisfy both the device and IOMMU's requirements. Maybe I misunderstand the constants on sparc and PAGE_SHIFT is fine there too? -Nish -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
