RE: [virtio-dev] Re: [virtio-comment] Re: [VIRTIO PCI PATCH v5 1/1] transport-pci: Add freeze_mode to virtio_pci_common_cfg

Parav Pandit
2023-09-20T06:58:55Z

> From: Chen, Jiqian <Jiqian.Chen@amd.com>
> Sent: Wednesday, September 20, 2023 12:03 PM

> If driver write 0 to reset device, can the SUSPEND bit be cleared?
It must as reset operation, resets everything else and so the suspend too.

> (pci_pm_resume->virtio_pci_restore->virtio_device_restore-
> >virtio_reset_device)
> If SUSPEND is cleared, then during the reset process in Qemu, I can't judge if
> the reset request is from guest restore process or not, and then I can't change
> the reset behavior.
Reset should not be influenced by suspend.
Suspend should do the work of suspend and reset to do the reset.

The problem to overcome in [1] is, resume operation needs to be synchronous as it involves large part of context to resume back, and hence just asynchronously setting DRIVER_OK is not enough.
The sw must verify back that device has resumed the operation and ready to answer requests.

This is slightly different flow than setting the DRIVER_OK for the first time device initialization sequence as it does not involve large restoration.

So, to merge two ideas, instead of doing DRIVER_OK to resume, the driver should clear the SUSPEND bit and verify that it is out of SUSPEND.

Because driver is still in _OK_ driving the device flipping the SUSPEND bit.