On Wed, 22 Jun 2022 at 12:57, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: > > > On 22.06.2022 11:14, Robin Murphy wrote: > > On 2022-06-21 20:57, Sam Protsenko wrote: > >> Hi Marek, > >> > >> On Fri, 21 Jan 2022 at 14:31, Marek Szyprowski > >> <m.szyprowski@xxxxxxxxxxx> 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. > > Well, Sam's question was about the Exynos SYSMMU own platform device, > not the device for which Exynos SYSMMU manages the IO virtual address > space. > > Simply add something like > > dma_set_mask(dev, DMA_BIT_MASK(36)); > Yep, that one worked, thanks! Just submitted a patch, with a bit of additions: [1]. [1] https://lkml.org/lkml/2022/7/2/269 > to the beginning of the exynos_sysmmu_probe(). This will disable SWIOTLB > and switch to DMA-direct for the Exynos SYSMMU platform device. > > > > (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...) > > Right, this has to be cleaned up. This driver was never used on systems > with kernel configuration for non-4KB pages. > > Best regards > -- > Marek Szyprowski, PhD > Samsung R&D Institute Poland >
