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

[Chen, Jiqian]

Hi Lingshan,
It seems you reply to the wrong email thread. They are not related to my patch.

On 2023/9/20 15:06, Zhu, Lingshan wrote:
> 
> 
> On 9/20/2023 2:58 PM, Parav Pandit wrote:
>>> 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 not live migration, all device status and other information still 
> stay in the device, no need to "resume" context, just resume running.
> 
> Like resume from a failed LM.
>>
>> 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.
> Please read the spec, it says:
> The driver MUST NOT clear a device status bit
> 
> 

-- 
Best regards,
Jiqian Chen.