On Wed, Dec 6, 2023 at 6:17 PM Michael S. Tsirkin <[email protected]> wrote: > > On Wed, Dec 06, 2023 at 05:16:04PM +0800, Jason Wang wrote: > > On Tue, Dec 5, 2023 at 6:58 PM David Stevens <[email protected]> wrote: > > > > > > On Tue, Dec 5, 2023 at 1:18 PM Jason Wang <[email protected]> wrote: > > > > > > > > On Mon, Dec 4, 2023 at 5:41 PM David Stevens <[email protected]> > > > > 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/[email protected]/ > > > > 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?
It looks to me we need: 1) Device side, if device can preserve state on d3hot, it may advertise no_soft_reset 2) Driver side, if driver sees no_soft_reset, it doesn't need to manually suspend and resume. But in the above patch, it only checks the existence of PM, it looks to me it needs to check no_soft_reset instead. > Maybe we need a new feature bit? Probably not. Thanks > > -- > MST > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
