feat(virtio): add virtqueue interrupt methods

[veqcc]

Description

Added virtqueue interrupt methods

• virtio_stop_vq_intr
• virtio_start_vq_intr

Related links

OpenBSD virtio_stop_vq_intr
https://github.com/openbsd/src/blob/9cb2b01c8c81819efa339598dd45ff164e968f48/sys/dev/pv/virtio.c#L960

OpenBSD virtio_start_vq_intr
https://github.com/openbsd/src/blob/9cb2b01c8c81819efa339598dd45ff164e968f48/sys/dev/pv/virtio.c#L980

How was this PR tested?

Tested in #465

Notes for reviewers

We currently don't support VIRTIO_F_RING_EVENT_IDX or VIRTIO_F_EVENT_IDX

[Koichi98]

https://github.com/openbsd/src/blob/9cb2b01c8c81819efa339598dd45ff164e968f48/sys/dev/pv/virtio.c#L997
It seems that vq_queued was incremented but not used for anything other than debugging purposes, so it was deleted?

[veqcc]

@Koichi98

https://github.com/openbsd/src/blob/9cb2b01c8c81819efa339598dd45ff164e968f48/sys/dev/pv/virtio.c#L997
It seems that vq_queued was incremented but not used for anything other than debugging purposes, so it was deleted?

Partially yes. vq_queued in OpenBSD is used for two purposes. Both are unnecessary for Awkernel for now.

1. debugging
2. DMA synchronization to make all changes visible to device: https://github.com/openbsd/src/blob/59c04fd1110661898186153cace43603c87b800e/sys/dev/pv/virtio.c#L291-L294

[Koichi98]

@veqcc

DMA synchronization to make all changes visible to device:

True.
So are we not implementing this virtio_check_vq()?

[veqcc]

@Koichi98

So are we not implementing this virtio_check_vq()?

Yes, I'm implementing similar functionality as interrupt as NetDevice trait.

fn interrupt(&self, irq: u16) -> Result<(), NetDevError { ... }

However, we do not care about cache in DMA yet, which means the following procedure can be skipped

	if (vq->vq_queued) {
		vq->vq_queued = 0;
		vq_sync_aring(sc, vq, BUS_DMASYNC_POSTWRITE);
	}