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    SubjectRe: [PATCH for-2.6.35] virtio-pci: disable msi at startup
    On Wed, 23 Jun 2010 18:35:55 +0300
    Avi Kivity <avi@redhat.com> wrote:

    > On 06/23/2010 06:26 PM, Michael S. Tsirkin wrote:
    > >
    > >
    > >>>
    > >>>
    > >>>>>> Shouldn't a reset be equivalent to power cycling?
    > >>>>>>
    > >>>>>>
    > >>>>>>
    > >>>>> If we did this, driver would need to restore registers
    > >>>>> such as BAR etc.
    > >>>>>
    > >>>>>
    > >>>>>
    > >>>> We could save/restore the registers we care about.
    > >>>>
    > >>>>
    > >>> It seems easier to clear registers we care about.
    > >>>
    > >> We know the registers we care about, we don't know the ones we don't.
    > >>
    > > If/when we use more registers, we can update driver to clear them on start.
    > >
    >
    > The kdump kernel may not load drivers for those extra devices.

    FLR or another type of reset also has the nice property of bringing the
    device into a known state. kexec/kdump has always been vulnerable to
    having devices in partial states when the new kernel loads; would be
    good to make it more robust.

    >
    > >> I'm talking about FLRing all cards, not just those you want to use.
    > >>
    > > reset using FLR/PM is complex because of the need to save/restore
    > > config space. Doing this on a crashing kernel sounds scary.
    > >
    >
    > Well, you only need to save/restore for the devices you use. The rest
    > you reset and forget.
    >
    > I don't really see why copying some config space is crazy.

    We could push any needed save/restore of core settings and regs into
    the PCI core like we do for PM. That would save a bunch of driver
    trouble...

    --
    Jesse Barnes, Intel Open Source Technology Center


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