On 1 August 2017 at 22:44, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > On Thu, Jul 13, 2017 at 10:26:40AM +0200, Greg Kroah-Hartman wrote: >> 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 :) > > Ping, in case Mathias is back from vacation :) Actually, Mathias already acked these changes, in reply to 2/2 -- 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
