Messages in this thread | | | Date | Wed, 22 Jun 2022 10:14:08 +0100 | Subject | Re: [RFC 2/3] iommu/samsung: Introduce Exynos sysmmu-v8 driver | From | Robin Murphy <> |
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On 2022-06-21 20:57, Sam Protsenko wrote: > Hi Marek, > > On Fri, 21 Jan 2022 at 14:31, Marek Szyprowski <m.szyprowski@samsung.com> wrote: > > [snip] > >> >> Well, for starting point the existing exynos-iommu driver is really >> enough. I've played a bit with newer Exyos SoCs some time ago. If I >> remember right, if you limit the iommu functionality to the essential >> things like mapping pages to IO-virtual space, the hardware differences >> between SYSMMU v5 (already supported by the exynos-iommu driver) and v7 >> are just a matter of changing a one register during the initialization >> and different bits the page fault reason decoding. You must of course >> rely on the DMA-mapping framework and its implementation based on >> mainline DMA-IOMMU helpers. All the code for custom iommu group(s) >> handling or extended fault management are not needed for the initial >> version. >> > > Thanks for the advice! Just implemented some testing driver, which > uses "Emulated Translation" registers available on SysMMU v7. That's > one way to verify the IOMMU driver with no actual users of it. It > works fine with vendor SysMMU driver I ported to mainline earlier, and > now I'm trying to use it with exynos-sysmmu driver (existing > upstream). If you're curious -- I can share the testing driver > somewhere on GitHub. > > I believe the register you mentioned is PT_BASE one, so I used > REG_V7_FLPT_BASE_VM = 0x800C instead of REG_V5_PT_BASE_PFN. But I > didn't manage to get that far, unfortunately, as > exynos_iommu_domain_alloc() function fails in my case, with BUG_ON() > at this line: > > /* For mapping page table entries we rely on dma == phys */ > BUG_ON(handle != virt_to_phys(domain->pgtable)); > > One possible explanation for this BUG is that "dma-ranges" property is > not provided in DTS (which seems to be the case right now for all > users of "samsung,exynos-sysmmu" driver). Because of that the SWIOTLB > is used for dma_map_single() call (in exynos_iommu_domain_alloc() > function), which in turn leads to that BUG. At least that's what > happens in my case. The call chain looks like this: > > exynos_iommu_domain_alloc() > v > dma_map_single() > v > dma_map_single_attrs() > v > dma_map_page_attrs() > v > dma_direct_map_page() // dma_capable() == false > v > swiotlb_map() > v > swiotlb_tbl_map_single() > > And the last call of course always returns the address different than > the address for allocated pgtable. E.g. in my case I see this: > > handle = 0x00000000fbfff000 > virt_to_phys(domain->pgtable) = 0x0000000880d0c000 > > Do you know what might be the reason for that? I just wonder how the > SysMMU driver work for all existing Exynos platforms right now. I feel > I might be missing something, like some DMA option should be enabled > so that SWIOTLB is not used, or something like that. Please let me > know if you have any idea on possible cause. The vendor's SysMMU > driver is kinda different in that regard, as it doesn't use > dma_map_single(), so I don't see such issue there.
If this SysMMU version is capable of addressing more than 32 bits, then exynos_iommu_probe_device() should set its DMA masks appropriately.
(as a side note since I looked, the use of PAGE_SIZE/PAGE_SHIFT in the driver looks wrong, since I can't imagine that the hardware knows whether Linux is using 4KB, 16KB or 64KB and adjusts itself accordingly...)
Robin.
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