Re: [RFC QEMU PATCH v8 2/2] virtio-pci: implement No_Soft_Reset bit

[Chen, Jiqian]

On 2024/3/28 20:36, Michael S. Tsirkin wrote:
>>>> +}
>>>> +
>>>>  static void virtio_pci_bus_reset_hold(Object *obj)
>>>>  {
>>>>      PCIDevice *dev = PCI_DEVICE(obj);
>>>>      DeviceState *qdev = DEVICE(obj);
>>>>  
>>>> +    if (virtio_pci_no_soft_reset(dev)) {
>>>> +        return;
>>>> +    }
>>>> +
>>>>      virtio_pci_reset(qdev);
>>>>  
>>>>      if (pci_is_express(dev)) {
>>>> @@ -2484,6 +2511,8 @@ static Property virtio_pci_properties[] = {
>>>>                      VIRTIO_PCI_FLAG_INIT_LNKCTL_BIT, true),
>>>>      DEFINE_PROP_BIT("x-pcie-pm-init", VirtIOPCIProxy, flags,
>>>>                      VIRTIO_PCI_FLAG_INIT_PM_BIT, true),
>>>> +    DEFINE_PROP_BIT("x-pcie-pm-no-soft-reset", VirtIOPCIProxy, flags,
>>>> +                    VIRTIO_PCI_FLAG_PM_NO_SOFT_RESET_BIT, false),
>>>>      DEFINE_PROP_BIT("x-pcie-flr-init", VirtIOPCIProxy, flags,
>>>>                      VIRTIO_PCI_FLAG_INIT_FLR_BIT, true),
>>>>      DEFINE_PROP_BIT("aer", VirtIOPCIProxy, flags,
>>>
>>> I am a bit confused about this part.
>>> Do you want to make this software controllable?
>> Yes, because even the real hardware, this bit is not always set.
> 
> So which virtio devices should and which should not set this bit?
This depends on the scenario the virtio-device is used, if we want to trigger 
an internal soft reset for the virtio-device during S3, this bit shouldn't be 
set.
In my use case on my environment, I don't want to reset virtio-gpu during S3,
because once the display resources are destroyed, there are not enough 
information to re-create them, so this bit should be set.
Making this bit software controllable is convenient for users to take their own 
choices.

> 
>>> Or should this be set to true by default and then
>>> changed to false for old machine types?
>> How can I do so?
>> Do you mean set this to true by default, and if old machine types don't need 
>> this bit, they can pass false config to qemu when running qemu?
> 
> No, you would use compat machinery. See how is x-pcie-flr-init handled.
> 
> 

-- 
Best regards,
Jiqian Chen.