Re: [PATCH 4/4] virtio-mmio: cleanup reset

[Paolo Bonzini <pbonzini@redhat.com>]

On 6/9/22 14:22, Cornelia Huck wrote:
>> -    if (proxy->legacy) {
>> -        return;
>> -    }
>> +    virtio_bus_reset(&proxy->bus);
>>   
>> -    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
>> -        proxy->vqs[i].enabled = 0;
>> +    if (!proxy->legacy) {
>> +        for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
>> +            proxy->vqs[i].enabled = 0;
>> +        }
>>       }
>>   }
>
> The more I look at this, the more confused I get.
> 
> The current code calls soft_reset when the driver sets the status to 0,
> after already having called virtio_reset().

Yes, that's before the patch.

> But doesn't virtio_reset() ultimately already trigger the virtio-mmio
> reset routine, which sets enabled to 0 for all queues? Why do that
> again? (And why is soft_reset a "soft reset"?)
No, it does not set enabled = 0 because "enabled" is specific to 
virtio-mmio (it is read by VIRTIO_MMIO_QUEUE_READY, which is only 
available in virtio-mmio 1.0 devices).  In fact it is stored in 
proxy->vqs[], while virtio_reset only resets fields in vdev->vq[].

k->reset() instead triggers the *device* reset routine (e.g. 
virtio_blk_reset).  So what makes it "soft" is that the various queue 
addresses remain there, and can be enabled just by writing 1 to 
VIRTIO_MMIO_QUEUE_READY for every queue.

Paolo