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    SubjectRe: [PATCH 4/4] PCI: quirk Atheros AR93xx to avoid bus reset
    On Thu, Jan 8, 2015 at 1:30 PM, Alex Williamson
    <alex.williamson@redhat.com> wrote:
    > On Thu, 2015-01-08 at 09:07 -0700, Bjorn Helgaas wrote:
    >> On Fri, Nov 21, 2014 at 11:24:27AM -0700, Alex Williamson wrote:
    >> > Reports against the TL-WDN4800 card indicate that PCI bus reset of
    >> > this Atheros device cause system lock-ups and resets. I've also
    >> > been able to confirm this behavior on multiple systems. The device
    >> > never returns from reset and attempts to access config space of the
    >> > device after reset result in hangs. Blacklist bus reset for the
    >> > device to avoid this issue.
    >> >
    >> > Reported-by: Andreas Hartmann <andihartmann@freenet.de>
    >> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    >> > Tested-by: Andreas Hartmann <andihartmann@freenet.de>
    >>
    >> If I understand correctly, these two (patches 3 & 4) fix a v3.14 regression
    >> caused by 425c1b223dac ("PCI: Add Virtual Channel to save/restore support").
    >>
    >> If so, these should go to for-linus for v3.19. What about patches 1 & 2?
    >> Do they fix a regression? Is there a pointer to a bugzilla or problem
    >> report about that issue?
    >>
    >> I don't understand the connection between 425c1b223dac and
    >> PCI_DEV_FLAGS_NO_BUS_RESET, because 425c1b223dac doesn't seem to do any
    >> resets. Is that the wrong commit, or can you outline the connection for
    >> me?
    >
    > TBH, I don't have a lot of faith in associating this to 425c1b223dac,
    > I'm not sure how Andreas' bisect landed there. IME, this device cannot,
    > and has never been able to handle a bus reset. A simple setpci
    > experiment on the commandline can confirm this. What I think happened
    > is that with the PCI bus reset infrastructure we added, we switched QEMU
    > to prefer PCI bus resets over things like PM D3hot->D0 resets. So it's
    > just more prolific use of bus resets by userspace.

    Maybe it's not 425c1b223dac, but it seems pretty clear that it really
    is a regression from the user point of view. I'm sure Andreas was
    using the same user-space for v3.13 and v3.14.

    Testing 425c1b223dac^ (the predecessor of 425c1b223dac) and
    425c1b223dac would confirm the bisect results.

    If it really turns out that 425c1b223dac^ works and 425c1b223dac
    fails, maybe we could learn something interesting by adding debug
    output to the various reset flavors and comparing the output?

    > There's also no regression in 1 & 2, PM reset has never done anything
    > useful on those devices. Thanks,

    Since 1 & 2 don't fix a regression, I think what I should do is apply
    3 & 4 to for-linus for v3.19, then apply 1 & 2 on top as v3.20
    material.

    Bjorn

    >> > ---
    >> >
    >> > drivers/pci/quirks.c | 14 ++++++++++++++
    >> > 1 file changed, 14 insertions(+)
    >> >
    >> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
    >> > index 561e10d..ebbd5b4 100644
    >> > --- a/drivers/pci/quirks.c
    >> > +++ b/drivers/pci/quirks.c
    >> > @@ -3029,6 +3029,20 @@ static void quirk_no_pm_reset(struct pci_dev *dev)
    >> > DECLARE_PCI_FIXUP_CLASS_HEADER(PCI_VENDOR_ID_ATI, PCI_ANY_ID,
    >> > PCI_CLASS_DISPLAY_VGA, 8, quirk_no_pm_reset);
    >> >
    >> > +static void quirk_no_bus_reset(struct pci_dev *dev)
    >> > +{
    >> > + dev->dev_flags |= PCI_DEV_FLAGS_NO_BUS_RESET;
    >> > +}
    >> > +
    >> > +/*
    >> > + * Atheros AR93xx chips do not behave after a bus reset. The device will
    >> > + * throw a Link Down error on AER capable system and regardless of AER,
    >> > + * config space of the device is never accessible again and typically
    >> > + * causes the system to hang or reset when access is attempted.
    >> > + * http://www.spinics.net/lists/linux-pci/msg34797.html
    >> > + */
    >> > +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_ATHEROS, 0x0030, quirk_no_bus_reset);
    >> > +
    >> > #ifdef CONFIG_ACPI
    >> > /*
    >> > * Apple: Shutdown Cactus Ridge Thunderbolt controller.
    >> >
    >
    >
    >


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