> (cc: IOMMU & page_frag_alloc maintainers) > > On Tue, Jan 15, 2019 at 10:04:01AM +0100, Lorenzo Bianconi wrote: > > > On Mon, Jan 14, 2019 at 1:18 AM Lorenzo Bianconi > > > <lorenzo.bianconi@xxxxxxxxxx> wrote: > > > > > > > > > On Sun, Jan 13, 2019 at 11:00 AM Lorenzo Bianconi > > > > > <lorenzo.bianconi@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > On Sun, Jan 13, 2019 at 5:33 AM, Lorenzo Bianconi <lorenzo.bianconi@xxxxxxxxxx> wrote: > > > > > > > > > > > > > > Direct. No VM used. This is the only peripheral causing this issue. > > > > > > > > > > > > > > Is the device connected to a usb3.0 port? If so, could you please try to connect the dongle to a 2.0 one? > > > > > > > > > > > > > > I tried through a USB 2.0 port. Shouldn't make a difference as they both use the xhci driver. > > > > > > > > > > > > > > > > > > > mt76x2u supports scatter-gather on usb 3.0 (not on 2.0) > > > > > Tried a USB 3 port. Same result. > > > > > > > > > > > > > Could you please double check if IOMMU is enabled? > > > > > > > > > > > > > > > > > > > Have you tried to disable it? Does it make any difference? > > > > > No idea how. UEFI doesn't seem to show anything similar. > > > > > > > > > > Similar bug report: https://bugzilla.kernel.org/show_bug.cgi?id=202241 > > FWIW: I provided some patches in the bugzilla, which were reported to > solve the problem. But I looking for confirmation if both are needed: > > 0001-mt76x02u-use-usb_bulk_msg-to-upload-firmware.patch > 0002-mt76usb-do-not-use-compound-head-page-for-SG-I-O.patch > > Or problem can be solved by just one of it (either first or second). > > Additionally I'm not 100% sure if > > 0002-mt76usb-do-not-use-compound-head-page-for-SG-I-O.patch > > is correct. So perhaps some IOMMU maintainer could look at it. > > > > > You should be able to disable iommu using GRUB_CMDLINE_LINUX in > > > > /etc/default/grub (I guess setting iommu=off and reinstalling grub) > > > > https://wiki.gentoo.org/wiki/IOMMU_SWIOTLB > > > Yep. Working great now. I wonder what mt76 is doing to cause the crash though... > > > > Thanks for bisecting the issue. > > Lorenzo, what you mean by 'bisecting' here ? Someone did 'git bisect' > on this issue? > Hi Stanislaw, I was meaning 'help bisecting' the issue > > I think amd iommu does not support well usb scatter-gather > > (used by default in mt76u). I am working on a series in order to add the possibility to > > disable it. > > Even if that true that AMD IOMMU does not support 'well' SG (what I think > is not true) disabling SG in mt76 driver is not right solution. Right > solution would be propagate the issue to AMD IOMMU maintainers > (already CCed). I meant that AMD iommu seems to have different constraints respect to Intel one. Regards, Lorenzo > > One problem in mt76 is page_frag_alloc() usage with different sizes. > page_frag_alloc() unlike like other allocators do not assure alignment > and relay on callers to provide buffers sizes that are aligned. > Unaligned buffer might then not be appropriate for DMA. > > Another issue is that dma_map_sg() & dma_map_page() may require some > constraints. I'm not sure about that and I want to clarify that with > CCed mm maintainers. I think DMA drivers may expect sg->offset < PAGE_SIZE > for both dma_map_sg() and dma_map_page(). Additionally dma_map_page() > maight expect that offset & length specify buffer within one page. > > Stanislaw
