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

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Date:   Tue, 1 Aug 2017 22:53:01 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-usb <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 0/2] Workaround for uPD72020x USB3 chips

On 1 August 2017 at 22:44, Bjorn Helgaas <helgaas@...nel.org> 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