On Wed, Jul 12, 2017 at 10:12:34PM -0500, Bjorn Helgaas wrote: > 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. The xhci maintainer is on vacation, let's wait a week for him to get back to get this. Given the long time that this has been broken on this hardware, I think we can wait another week just fine :) thanks, greg k-h
