Re: The virtio-gpu does not work with virtio_mmio.c transport

Hi Markku,

On Wed, 29 Jul 2026, Markku Rossi wrote:

> >Synopsis: virtio-gpu does not work with virtio_mmio.c
> >Category: kernel
> >Environment:
>         System      : OpenBSD 7.9
>         Details     : OpenBSD 7.9 (GOEMU) #1: Wed Jul 29 07:01:37 CEST 2026
>                          [email protected]:
> /usr/src/sys/arch/ris
> cv64/compile/GOEMU
> 
>         Architecture: OpenBSD.riscv64
>         Machine     : riscv64
> >Description:
> 
> I am developing my own RISC-V 64 emulator
> (https://github.com/markkurossi/riscv). The emulator implements only
> the VirtIO MMIO drivers. On OpenBSD, the VirtIO GPU (virtio-gpu)
> device does not initialize with the `virtio_mmio.c' driver. The
> `viogpu.c' driver checks:
> 
> if (!vsc->sc_version_1) {
> printf(": requires virtio version 1\n");
> goto err;
> }
> 
> The `vsc->sc_version_1' field is initialized in the `virtio_pci.c'
> file but not in the `virtio_mmio.c' file. The `virtio_mmio.c' does a
> version check and a trivial fix is to initialize the
> `vsc->sc_version_1' field if `sc->sc_version == 2' (patch below).

There is more stuff missing for correct virtio 1.x mmio support. Your diff 
alone did not make vio(4) attached at virtio-mmio work on linux/KVM/arm64. 
Does the diff below work for you?

Cheers,
Stefan

diff --git a/sys/dev/fdt/virtio_mmio.c b/sys/dev/fdt/virtio_mmio.c
index f673c7dcd4c..de7c529b989 100644
--- a/sys/dev/fdt/virtio_mmio.c
+++ b/sys/dev/fdt/virtio_mmio.c
@@ -119,7 +119,6 @@ struct virtio_mmio_softc {
 	void			*sc_ih;
 
 	int			sc_config_offset;
-	uint32_t		sc_version;
 };
 
 struct virtio_mmio_attach_args {
@@ -183,12 +182,16 @@ virtio_mmio_setup_queue(struct virtio_softc *vsc, struct virtqueue *vq,
 	    vq->vq_index);
 	bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_NUM,
 	    bus_space_read_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_NUM_MAX));
-	if (sc->sc_version == 1) {
+	if (!vsc->sc_version_1) {
 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 		    VIRTIO_MMIO_QUEUE_ALIGN, PAGE_SIZE);
 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 		    VIRTIO_MMIO_QUEUE_PFN, addr / VIRTIO_PAGE_SIZE);
 	} else {
+		if (addr == 0) {
+			bus_space_write_4(sc->sc_iot, sc->sc_ioh,
+			    VIRTIO_MMIO_QUEUE_READY, 0);
+		}
 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 		    VIRTIO_MMIO_QUEUE_DESC_LOW, addr);
 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
@@ -205,8 +208,10 @@ virtio_mmio_setup_queue(struct virtio_softc *vsc, struct virtqueue *vq,
 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 		    VIRTIO_MMIO_QUEUE_USED_HIGH,
 		    (addr + vq->vq_usedoffset) >> 32);
-		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
-		    VIRTIO_MMIO_QUEUE_READY, 1);
+		if (addr != 0) {
+			bus_space_write_4(sc->sc_iot, sc->sc_ioh,
+			    VIRTIO_MMIO_QUEUE_READY, 1);
+		}
 	}
 }
 
@@ -259,7 +264,7 @@ virtio_mmio_attach(struct device *parent, struct device *self, void *aux)
 	struct fdt_attach_args *faa = aux;
 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)self;
 	struct virtio_softc *vsc = &sc->sc_sc;
-	uint32_t id, magic;
+	uint32_t id, magic, version;
 	struct virtio_mmio_attach_args vma = { { 0 }, faa };
 
 	if (faa->fa_nreg < 1) {
@@ -281,11 +286,20 @@ virtio_mmio_attach(struct device *parent, struct device *self, void *aux)
 		return;
 	}
 
-	sc->sc_version = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
+	version = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
 	    VIRTIO_MMIO_VERSION);
-	if (sc->sc_version < 1 || sc->sc_version > 2) {
-		printf(": unknown version 0x%02x; giving up\n", sc->sc_version);
-		return;
+	switch (version) {
+		case 1:
+			/* virtio 0.9 */
+			break;
+		case 2:
+			/* virtio 1.x */
+			vsc->sc_version_1 = 1;
+			break;
+		default:
+			printf(": unknown version 0x%02x; giving up\n",
+			    version);
+			return;
 	}
 
 	id = bus_space_read_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_DEVICE_ID);
@@ -297,7 +311,7 @@ virtio_mmio_attach(struct device *parent, struct device *self, void *aux)
 	if (id == 0)
 		return;
 
-	if (sc->sc_version == 1)
+	if (!vsc->sc_version_1)
 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 		    VIRTIO_MMIO_GUEST_PAGE_SIZE, PAGE_SIZE);
 
@@ -408,10 +422,20 @@ virtio_mmio_negotiate_features(struct virtio_softc *vsc,
 	}
 
 	vsc->sc_driver_features |= VIRTIO_F_ANY_LAYOUT;
+	if (vsc->sc_version_1) {
+		vsc->sc_driver_features |= VIRTIO_F_VERSION_1;
+		/* notify on empty is 0.9 only */
+		vsc->sc_driver_features &= ~VIRTIO_F_NOTIFY_ON_EMPTY;
+	}
+
 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 	    VIRTIO_MMIO_HOST_FEATURES_SEL, 0);
 	host = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
-				VIRTIO_MMIO_HOST_FEATURES);
+	     VIRTIO_MMIO_HOST_FEATURES);
+	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
+	    VIRTIO_MMIO_HOST_FEATURES_SEL, 1);
+	host |= (uint64_t)bus_space_read_4(sc->sc_iot, sc->sc_ioh,
+	    VIRTIO_MMIO_HOST_FEATURES) << 32;
 	neg = host & vsc->sc_driver_features;
 #if VIRTIO_DEBUG
 	if (guest_feature_names)
@@ -420,7 +444,33 @@ virtio_mmio_negotiate_features(struct virtio_softc *vsc,
 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
 	    VIRTIO_MMIO_GUEST_FEATURES_SEL, 0);
 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
-			  VIRTIO_MMIO_GUEST_FEATURES, neg);
+	    VIRTIO_MMIO_GUEST_FEATURES, neg);
+	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
+	    VIRTIO_MMIO_GUEST_FEATURES_SEL, 1);
+	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
+	    VIRTIO_MMIO_GUEST_FEATURES, neg >> 32);
+
+	if (vsc->sc_version_1) {
+		virtio_mmio_set_status(vsc,
+		    VIRTIO_CONFIG_DEVICE_STATUS_FEATURES_OK);
+		if ((virtio_mmio_get_status(vsc) &
+		    VIRTIO_CONFIG_DEVICE_STATUS_FEATURES_OK) == 0) {
+			printf("%s: Feature negotiation failed\n",
+			    vsc->sc_dev.dv_xname);
+			virtio_mmio_set_status(vsc,
+			    VIRTIO_CONFIG_DEVICE_STATUS_FAILED);
+			return ENXIO;
+		}
+		if ((neg & VIRTIO_F_VERSION_1) == 0) {
+#if VIRTIO_DEBUG
+			printf("%s: Host rejected Version_1\n", __func__);
+#endif
+			virtio_mmio_set_status(vsc,
+			    VIRTIO_CONFIG_DEVICE_STATUS_FAILED);
+			return EINVAL;
+		}
+	}
+
 	vsc->sc_active_features = neg;
 	if (neg & VIRTIO_F_RING_INDIRECT_DESC)
 		vsc->sc_indirect = 1;
@@ -519,18 +569,22 @@ virtio_mmio_intr(void *arg)
 {
 	struct virtio_mmio_softc *sc = arg;
 	struct virtio_softc *vsc = &sc->sc_sc;
-	int isr, r = 0;
+	int isr, r = 0, handled = 0;
 
 	/* check and ack the interrupt */
 	isr = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
 			       VIRTIO_MMIO_INTERRUPT_STATUS);
-	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
-			  VIRTIO_MMIO_INTERRUPT_ACK, isr);
 	if ((isr & VIRTIO_MMIO_INT_CONFIG) &&
-	    (vsc->sc_config_change != NULL))
+	    (vsc->sc_config_change != NULL)) {
 		r = (vsc->sc_config_change)(vsc);
-	if ((isr & VIRTIO_MMIO_INT_VRING))
+		handled |= VIRTIO_MMIO_INT_CONFIG;
+	}
+	if ((isr & VIRTIO_MMIO_INT_VRING)) {
 		r |= virtio_check_vqs(vsc);
+		handled |= VIRTIO_MMIO_INT_VRING;
+	}
+	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
+			  VIRTIO_MMIO_INTERRUPT_ACK, handled);
 
 	return r;
 }
diff --git a/sys/dev/pv/if_vio.c b/sys/dev/pv/if_vio.c
index 8942b02857a..cb1dd8bf003 100644
--- a/sys/dev/pv/if_vio.c
+++ b/sys/dev/pv/if_vio.c
@@ -685,6 +685,8 @@ negotiate:
 		 */
 		want_tso = 0;
 		virtio_reset(vsc);
+		virtio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_ACK);
+		virtio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_DRIVER);
 		goto negotiate;
 	}
 
@@ -702,6 +704,8 @@ negotiate:
 			device_mtu = 0;
 			want_mtu = 0;
 			virtio_reset(vsc);
+			virtio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_ACK);
+			virtio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_DRIVER);
 			goto negotiate;
 		}
 	}