Re: [virtio-comment] [PATCH v3 1/1] Define a low power mode for devices

[Jason Wang <jasowang@redhat.com>]

On Tue, Dec 5, 2023 at 6:58âPM David Stevens <stevensd@chromium.org> wrote:
>
> On Tue, Dec 5, 2023 at 1:18âPM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Mon, Dec 4, 2023 at 5:41âPM David Stevens <stevensd@chromium.org> wrote:
> > >
> > > Define a low power mode for virtio devices where the devices are
> > > expected to maintain their state. This gives drivers an option for power
> > > management besides simply resetting their device. In the virtualization
> > > use case, this allows the guest to be suspended even with stateful
> > > virtio devices like gpu and fs.
> > >
> > > Low power mode is primarily defined at the transport layer. The only
> > > part that depends on device-type specific details is whether a given
> > > virtqueue is device driven or driver driven.
> > >
> > > This change only defines the transport-specific implementation for
> > > Virtio over PCI.
> >
> > A dumb question, if this is only for PCI, can the device just
> > implement no_soft_reset via PMC?
>
> This is basically No_Soft_Reset, yes. If a change similar to [1] would
> be acceptable based only on the No_Soft_Reset bit even with no concept
> of power management in the virtio spec, then I personally don't have
> any problems with that.
>
> [1] https://lore.kernel.org/lkml/20231113055138.117392-1-stevensd@chromium.org/

So if I read the code correctly, the current Qemu advertises PM but
without no_soft_reset.

So this patch seems to break e.g virtio-net and doesn't fix virtio-GPU.

Thanks

>
> -David
>