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Subject: Re: [virtio-comment] [PATCH v3 1/1] Define a low power mode for devices
On Wed, Dec 06, 2023 at 05:16:04PM +0800, Jason Wang wrote: > 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 > > what is the breakage exactly? Maybe we need a new feature bit? -- MST
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