On Thu, 11 Aug 2016 10:06:19 +0530 Anup Patel <anup.patel@xxxxxxxxxxxx> wrote: > 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? Yes, it went in during the most recent merge window for v4.8: 9698cbf vfio: platform: support No-IOMMU mode > 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 devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
