virtio mmio reset - driver requirements

I noticed this in virtio spec for PCI transport based devices:

"After writing 0 to device_status, the driver MUST wait for a read of device_status to return 0 before reinitializing the device."

I was wondering why the spec does not recommend a similar "wait after writing 0
to status register" for other transports such as MMIO.

Even the Linux code for virtio_mmio does not have any such wait:

static void vm_reset(struct virtio_device *vdev)

{
        struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);

        /* 0 status means a reset. */
        writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
}

Does that assume that backends are implemented in software when MMIO writes result in trap and backend synchronously does everything needed to handle reset
as part of trap handling? Wouldn't it break if we were to have backends implemented in hardware device accessed via MMIO transport?

Thanks
vatsa

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