Re: [virtio-comment] [PATCH RFC] virtio: introduce VIRTIO_F_DEVICE_STOP

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 13 Jan 2021 10:52:32 +0800
Jason Wang <jasowang@redhat.com> wrote:

> On 2021/1/12 äå8:13, Cornelia Huck wrote:
> > On Tue, 12 Jan 2021 11:27:20 +0800
> > Jason Wang <jasowang@redhat.com> wrote:
> >  
> >> On 2021/1/12 äå2:16, Cornelia Huck wrote:  
> >>> On Wed, 30 Dec 2020 16:15:47 +0800
> >>> Jason Wang <jasowang@redhat.com> wrote:
> >>>     
> >>>> On 2020/12/29 äå9:35, Halil Pasic wrote:  
> >>>>> On Mon, 28 Dec 2020 15:01:57 +0800
> >>>>> Jason Wang <jasowang@redhat.com> wrote:
> >>>>>        
> >>>>>> Some part of the virtio has enforced an asynchronous interface during reset:
> >>>>>>
> >>>>>> For MMIO the spec said:
> >>>>>>
> >>>>>> """
> >>>>>>
> >>>>>> To stop using the queue the driver MUST write zero (0x0) to this
> >>>>>> QueueReady and MUST read the value back to ensure synchronization.
> >>>>>>
> >>>>>> """  
> >>>>> I read the MMIO quote like a single read is sufficient to ensure
> >>>>> synchronization. I.e. it does not require a loop which waits for
> >>>>> the read to yield the expected value.
> >>>>>        
> >>>>>> For PCI it said:
> >>>>>>
> >>>>>> """
> >>>>>>
> >>>>>> After writing 0 to device_status, the driver MUST wait for a read of
> >>>>>> device_status to return 0 before reinitializing the device.
> >>>>>>
> >>>>>> """  
> >>>>> Yes, this does sound like a loop. And that's what Linux does. But this
> >>>>> is transport (PCI) specific. On a spec level, a reset is a distinct
> >>>>> operation from setting device status (to 0).  
> >>>> I'm not sure or it looks unclear to me for this point.
> >>>>
> >>>> E.g the device reset is mentioned in "Device Status Field" belongs to
> >>>> "Basic Facilities of a Virtio Device". But there's no "Device Reset" in
> >>>> "Basic Facilities of a Virtio Device".  
> >>> I think it should be, just to make clear what a driver-initiated reset
> >>> of a device actually resets (and that the method for doing so is
> >>> transport-specific.)  
> >>
> >> Then we need some clarifications in the spec. It would be easily imply
> >> that reset is part of device status after reading "Basic Facilities of a
> >> Virtio Device".  
> > I can try to come up with a patch.  
> 
> 
> Thanks

Attempt here:

https://lists.oasis-open.org/archives/virtio-comment/202101/msg00020.html