lkml.org 
[lkml]   [2017]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/2] Workaround for uPD72020x USB3 chips
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 :)

\
 
 \ /
  Last update: 2017-08-01 23:45    [W:0.081 / U:11.760 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site