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    SubjectRe: [PATCH v4 2/2] PCI: Enable NO_BUS_RESET quirk for Nvidia GPUs
    On Fri, Apr 30, 2021 at 05:11:23PM -0500, Shanker R Donthineni wrote:
    > Thanks Bjorn for reviewing patch.
    >
    > On 4/30/21 12:01 PM, Bjorn Helgaas wrote:
    > > External email: Use caution opening links or attachments
    > >
    > >
    > > On Wed, Apr 28, 2021 at 07:49:07PM -0500, Shanker Donthineni wrote:
    > >> On select platforms, some Nvidia GPU devices do not work with SBR.
    > >> Triggering SBR would leave the device inoperable for the current
    > >> system boot. It requires a system hard-reboot to get the GPU device
    > >> back to normal operating condition post-SBR. For the affected
    > >> devices, enable NO_BUS_RESET quirk to fix the issue.
    > > Since 1/2 adds _RST support, should I infer that _RST works on these
    > > Nvidia GPUs even though SBR does not? If so, how does _RST do the
    > > reset?
    > Yes, _RST method works but not SBR. The _RST method in DSDT-AML uses
    > platform-specific initialization steps outside of the GPU BARs for resetting
    > the GPU device.

    Obviously _RST only works for built-in devices, since there's no AML
    for plug-in devices, right? So if there's a plug-in card with this
    GPU, neither SBR nor _RST will work?

    > > Do you have a root cause for why SBR doesn't work?
    > It is a hardware implementation specific issue. GPU end-point device
    > is inoperative after receiving SBR from the RP/SwitchPort. This quirk is
    > to prevent SBR.

    That's not a root cause; it's basically still "it doesn't work." But
    OK.

    I'm wondering if we should log something to dmesg in
    quirk_no_bus_reset(), quirk_no_pm_reset(), quirk_no_flr(), etc., just
    so we have a hint about the fact that resets won't work quite as
    expected on these devices.

    Bjorn

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