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From:   Jason Wang <jasowang@redhat.com>
Date:   Tue, 12 Dec 2023 11:01:53 +0800
Message-ID: <CACGkMEs_MajTFxGVcK5R8oqQzTxuL4Pm=uUnOonDczWzqaucsw@mail.gmail.com>
Subject: Re: [PATCH v2] virtio: Add support for no-reset virtio PCI PM
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     David Stevens <stevensd@chromium.org>,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
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On Tue, Dec 12, 2023 at 12:37=E2=80=AFAM Michael S. Tsirkin <mst@redhat.com=
> wrote:
>
> On Fri, Dec 08, 2023 at 04:07:54PM +0900, David Stevens wrote:
> > If a virtio_pci_device supports native PCI power management and has the
> > No_Soft_Reset bit set, then skip resetting and reinitializing the devic=
e
> > when suspending and restoring the device. This allows system-wide low
> > power states like s2idle to be used in systems with stateful virtio
> > devices that can't simply be re-initialized (e.g. virtio-fs).
> >
> > Signed-off-by: David Stevens <stevensd@chromium.org>
>
> tagged, thanks!
> I'm still debating with myself whether we can classify this
> as a bugfix ... better not risk it I guess.

It might be suitable if there's a hypervisor that advertises
no_soft_reset (but it seems Qemu doesn't).

Thanks

>
> > ---
> > v1 -> v2:
> >  - Check the No_Soft_Reset bit
> >
> >  drivers/virtio/virtio_pci_common.c | 34 +++++++++++++++++++++++++++++-
> >  1 file changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio=
_pci_common.c
> > index c2524a7207cf..3a95ecaf12dc 100644
> > --- a/drivers/virtio/virtio_pci_common.c
> > +++ b/drivers/virtio/virtio_pci_common.c
> > @@ -492,8 +492,40 @@ static int virtio_pci_restore(struct device *dev)
> >       return virtio_device_restore(&vp_dev->vdev);
> >  }
> >
> > +static bool vp_supports_pm_no_reset(struct device *dev)
> > +{
> > +     struct pci_dev *pci_dev =3D to_pci_dev(dev);
> > +     u16 pmcsr;
> > +
> > +     if (!pci_dev->pm_cap)
> > +             return false;
> > +
> > +     pci_read_config_word(pci_dev, pci_dev->pm_cap + PCI_PM_CTRL, &pmc=
sr);
> > +     if (PCI_POSSIBLE_ERROR(pmcsr)) {
> > +             dev_err(dev, "Unable to query pmcsr");
> > +             return false;
> > +     }
> > +
> > +     return pmcsr & PCI_PM_CTRL_NO_SOFT_RESET;
> > +}
> > +
> > +static int virtio_pci_suspend(struct device *dev)
> > +{
> > +     return vp_supports_pm_no_reset(dev) ? 0 : virtio_pci_freeze(dev);
> > +}
> > +
> > +static int virtio_pci_resume(struct device *dev)
> > +{
> > +     return vp_supports_pm_no_reset(dev) ? 0 : virtio_pci_restore(dev)=
;
> > +}
> > +
> >  static const struct dev_pm_ops virtio_pci_pm_ops =3D {
> > -     SET_SYSTEM_SLEEP_PM_OPS(virtio_pci_freeze, virtio_pci_restore)
> > +     .suspend =3D virtio_pci_suspend,
> > +     .resume =3D virtio_pci_resume,
> > +     .freeze =3D virtio_pci_freeze,
> > +     .thaw =3D virtio_pci_restore,
> > +     .poweroff =3D virtio_pci_freeze,
> > +     .restore =3D virtio_pci_restore,
> >  };
> >  #endif
> >
> > --
> > 2.43.0.472.g3155946c3a-goog
>