On Mon, Jul 10, 2017 at 04:52:28PM +0100, Marc Zyngier wrote: > Ard and myself have just spent quite some time lately trying to pin > down an issue in the DMA code which was taking the form of a PCIe USB3 > controller issuing a DMA access at some bizarre address, and being > caught red-handed by the IOMMU. > > After much head scratching and most of a week-end spent on tracing the > damn thing, I'm now convinced that the DMA code is fine, the XHCI > driver is correct, but that the HW (a Renesas uPD720202 chip) is a > nasty piece of work. > > The issue is as follow: > > - EFI initializes the controller using physical addresses above the > 4GB limit (this is on an arm64 box where the memory starts at > 0x80_00000000...). > > - The kernel takes over, sends a XHCI reset to the controller, and > because we have an IOMMU sitting between the controller and memory, > provides *virtual* addresses. Trying to make things a bit faster for > our controller, it issues IOVAs in the low 4GB range). > > - Low and behold, the controller is now issuing transactions with a > 0x80 prefix in front of our IOVA. Yes, the same prefix that was > programmed during the EFI configuration. IOMMU fault, not happy. > > If the kernel is hacked to only generate IOVAs that are more than > 32bit wide, the HW behaves correctly. The only way I can explain this > behaviour is that the HW latches the top 32bit of the ERST (it is > always the ERST IOVA that appears in my traces) in some internal > register, and that the XHCI reset fails to clear it. Writing zero in > the top bits is not enough to clear it either. > > So far, the only solution we have for this lovely piece of kit is to > force a PCI reset at probe time, which puts it right. The patches are > pretty ugly, but that's the best I could come up with so far. > > Tested on a pair of AMD Opteron 1100 boxes with Renesas uPD720201 and > uPD720202 controllers. > > Marc Zyngier (2): > PCI: Implement pci_reset_function_locked > usb: host: pci_quirks: Force hard reset of Renesas uPD72020x USB > controller > > drivers/pci/pci.c | 35 +++++++++++++++++++++++++++++++++++ > drivers/usb/host/pci-quirks.c | 20 ++++++++++++++++++++ > drivers/usb/host/pci-quirks.h | 1 + > drivers/usb/host/xhci-pci.c | 7 +++++++ > include/linux/pci.h | 1 + > 5 files changed, 64 insertions(+) I provisionally applied this to pci/virtualization. I'd like to have an XHCI ack before going further, though. I assume this only affects boxes where the firmware uses addresses above 4GB, i.e., not very many? So this is v4.14 material? Or do you think it's important for v4.13? Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
