Hi Alex, On Thu, Aug 11, 2016 at 9:46 AM, Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Thu, 11 Aug 2016 09:30:19 +0530 > Anup Patel <anup.patel@xxxxxxxxxxxx> wrote: > >> Hi Arnd, >> >> On Wed, Aug 10, 2016 at 9:25 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: >> > On Monday, August 8, 2016 11:22:29 AM CEST Anup Patel wrote: >> >> The goal of this patchset is to improve UIO framework and UIO dmem >> >> driver to allow cache-coherent DMA accesses from user-space. >> >> >> >> This patchset is based on two previous patchsets: >> >> 1) [PATCH v5 0/6] UIO driver for APM X-Gene QMTM >> >> (Refer, http://www.spinics.net/lists/devicetree/msg58244.html) >> >> 2) [PATCH 0/4] Fix and extend uio_dmem_genirq >> >> (Refer, https://lkml.org/lkml/2016/5/17/141) >> >> >> >> We have adopted only patch0-3 of patchset1 which was abandoned >> >> long time back. We have taken care of last few unaddressed comments >> >> on these patches. >> >> >> >> The patchset2 is quite recent has been adopted entirely. We have >> >> taken care review comments on these patches too. >> >> >> >> This patchset is based on v4.7-rc7 tag and it is available in uio-v2 >> >> branch of https://github.com/Broadcom/arm64-linux.git >> > >> > >> > UIO devices are generally meant to be things that do not >> > perform DMA and that don't screw up the rest of the system >> > when misused. A device that is able to access any physical >> > memory doesn't belong into this category. The way that >> > uio_dmem_genirq.c gets around this is by requiring the device >> > to be created by some code that sets up a separate IOMMU >> > domain first, but the DT probing here doesn't do that. >> > Note that IOMMU domains typically use 32-bit addressing, >> > so the entire "dma_mask from property" dance isn't even >> > required. >> >> IMHO, UIO devices are meant for things that are not behind >> any IOMMU hardware. >> >> Yes, any mis-programming in user space using UIO can >> potentially screw-up the rest of the system but this is >> generally a known/assumed fact for people who are using UIO. >> >> > >> > Also, this seems to duplicate a lot of the work that >> > went into "vfio". Can you explain why we need another way >> > of doing the same thing here? >> >> We can only use "vfio" for devices that are behind some >> kind of IOMMU (Right??). For devices not having IOMMU >> support will have to use UIO for user space access. >> >> Particularly, there are lot of FPGA-based solutions and legacy >> hardware which do not have IOMMU support (devices on >> FPGA or specific devices). >> >> In our use case, we have some FPGA-based device which >> does not have IOMMU support and we are accessing this >> FPGA-based device from user-space. >> >> This patchset only tries to extend "uio" and "uio_dmem_genirq". >> There is no intention of duplicating what has been already >> done for "vfio". >> >> I do agree that "vfio" should eventually become defacto method >> of accessing devices in user space but that requires devices to >> always have IOMMU support. > > A vfio no-iommu mode exists since v4.5: > > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=03a76b60f8ba27974e2d252bc555d2c103420e15 It's good that we have "No-IOMMU" mode in VFIO now but I see that it's for vfio_pci only. Has this been extended for vfio_platform? We would certainly like to move to VFIO if "No-IOMMU" mode is available for vfio_platform devices because in-our use case devices are memory-mapped FPGA devices. Meanwhile, I would like to have this patchset for benefit of people who already using UIO. Regards, Anup -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
