linux-kernel - Re: [PATCH 0/2] Workaround for uPD72020x USB3 chips

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Message-ID: <20170713113706.GK4486@bhelgaas-glaptop.roam.corp.google.com>
Date:   Thu, 13 Jul 2017 06:37:06 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [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 :)

I'll be on vacation myself until the beginning of August, so no problem
with that.