Re: [PATCH 0/2] Workaround for uPD72020x USB3 chips
From: Bjorn Helgaas
Date: Wed Jul 12 2017 - 23:12:54 EST
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
> - 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
> 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?