xref: /openbsd/sys/dev/fdt/virtio_mmio.c (revision 9ea232b5)
1 /*	$OpenBSD: virtio_mmio.c,v 1.12 2024/01/15 02:35:23 dv Exp $	*/
2 /*	$NetBSD: virtio.c,v 1.3 2011/11/02 23:05:52 njoly Exp $	*/
3 
4 /*
5  * Copyright (c) 2014 Patrick Wildt <patrick@blueri.se>
6  * Copyright (c) 2012 Stefan Fritsch.
7  * Copyright (c) 2010 Minoura Makoto.
8  * All rights reserved.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
20  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
21  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
22  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
23  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
24  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
28  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29  */
30 
31 #include <sys/param.h>
32 #include <sys/systm.h>
33 #include <sys/kernel.h>
34 #include <sys/device.h>
35 #include <sys/mutex.h>
36 
37 #include <dev/pv/virtioreg.h>
38 #include <dev/pv/virtiovar.h>
39 
40 #include <machine/fdt.h>
41 
42 #include <dev/ofw/fdt.h>
43 #include <dev/ofw/openfirm.h>
44 
45 #define VIRTIO_MMIO_MAGIC		('v' | 'i' << 8 | 'r' << 16 | 't' << 24)
46 
47 #define VIRTIO_MMIO_MAGIC_VALUE		0x000
48 #define VIRTIO_MMIO_VERSION		0x004
49 #define VIRTIO_MMIO_DEVICE_ID		0x008
50 #define VIRTIO_MMIO_VENDOR_ID		0x00c
51 #define VIRTIO_MMIO_HOST_FEATURES	0x010
52 #define VIRTIO_MMIO_HOST_FEATURES_SEL	0x014
53 #define VIRTIO_MMIO_GUEST_FEATURES	0x020
54 #define VIRTIO_MMIO_GUEST_FEATURES_SEL	0x024
55 #define VIRTIO_MMIO_GUEST_PAGE_SIZE	0x028
56 #define VIRTIO_MMIO_QUEUE_SEL		0x030
57 #define VIRTIO_MMIO_QUEUE_NUM_MAX	0x034
58 #define VIRTIO_MMIO_QUEUE_NUM		0x038
59 #define VIRTIO_MMIO_QUEUE_ALIGN		0x03c
60 #define VIRTIO_MMIO_QUEUE_PFN		0x040
61 #define VIRTIO_MMIO_QUEUE_READY		0x044
62 #define VIRTIO_MMIO_QUEUE_NOTIFY	0x050
63 #define VIRTIO_MMIO_INTERRUPT_STATUS	0x060
64 #define VIRTIO_MMIO_INTERRUPT_ACK	0x064
65 #define VIRTIO_MMIO_STATUS		0x070
66 #define VIRTIO_MMIO_QUEUE_DESC_LOW	0x080
67 #define VIRTIO_MMIO_QUEUE_DESC_HIGH	0x084
68 #define VIRTIO_MMIO_QUEUE_AVAIL_LOW	0x090
69 #define VIRTIO_MMIO_QUEUE_AVAIL_HIGH	0x094
70 #define VIRTIO_MMIO_QUEUE_USED_LOW	0x0a0
71 #define VIRTIO_MMIO_QUEUE_USED_HIGH	0x0a4
72 #define VIRTIO_MMIO_CONFIG		0x100
73 
74 #define VIRTIO_MMIO_INT_VRING		(1 << 0)
75 #define VIRTIO_MMIO_INT_CONFIG		(1 << 1)
76 
77 #define DEVNAME(sc) (sc)->sc_dev.dv_xname
78 
79 /*
80  * XXX: Before being used on big endian arches, the access to config registers
81  * XXX: needs to be reviewed/fixed. The non-device specific registers are
82  * XXX: PCI-endian while the device specific registers are native endian.
83  */
84 
85 int		virtio_mmio_match(struct device *, void *, void *);
86 void		virtio_mmio_attach(struct device *, struct device *, void *);
87 int		virtio_mmio_detach(struct device *, int);
88 
89 void		virtio_mmio_kick(struct virtio_softc *, uint16_t);
90 uint8_t		virtio_mmio_read_device_config_1(struct virtio_softc *, int);
91 uint16_t	virtio_mmio_read_device_config_2(struct virtio_softc *, int);
92 uint32_t	virtio_mmio_read_device_config_4(struct virtio_softc *, int);
93 uint64_t	virtio_mmio_read_device_config_8(struct virtio_softc *, int);
94 void		virtio_mmio_write_device_config_1(struct virtio_softc *, int, uint8_t);
95 void		virtio_mmio_write_device_config_2(struct virtio_softc *, int, uint16_t);
96 void		virtio_mmio_write_device_config_4(struct virtio_softc *, int, uint32_t);
97 void		virtio_mmio_write_device_config_8(struct virtio_softc *, int, uint64_t);
98 uint16_t	virtio_mmio_read_queue_size(struct virtio_softc *, uint16_t);
99 void		virtio_mmio_setup_queue(struct virtio_softc *, struct virtqueue *, uint64_t);
100 void		virtio_mmio_set_status(struct virtio_softc *, int);
101 int		virtio_mmio_negotiate_features(struct virtio_softc *,
102     const struct virtio_feature_name *);
103 int		virtio_mmio_intr(void *);
104 
105 struct virtio_mmio_softc {
106 	struct virtio_softc	sc_sc;
107 
108 	bus_space_tag_t		sc_iot;
109 	bus_space_handle_t	sc_ioh;
110 	bus_size_t		sc_iosize;
111 	bus_dma_tag_t		sc_dmat;
112 
113 	void			*sc_ih;
114 
115 	int			sc_config_offset;
116 	uint32_t		sc_version;
117 };
118 
119 const struct cfattach virtio_mmio_ca = {
120 	sizeof(struct virtio_mmio_softc),
121 	virtio_mmio_match,
122 	virtio_mmio_attach,
123 	virtio_mmio_detach,
124 	NULL
125 };
126 
127 const struct cfattach virtio_mmio_fdt_ca = {
128 	sizeof(struct virtio_mmio_softc),
129 	NULL,
130 	virtio_mmio_attach,
131 	virtio_mmio_detach,
132 	NULL
133 };
134 
135 struct virtio_ops virtio_mmio_ops = {
136 	virtio_mmio_kick,
137 	virtio_mmio_read_device_config_1,
138 	virtio_mmio_read_device_config_2,
139 	virtio_mmio_read_device_config_4,
140 	virtio_mmio_read_device_config_8,
141 	virtio_mmio_write_device_config_1,
142 	virtio_mmio_write_device_config_2,
143 	virtio_mmio_write_device_config_4,
144 	virtio_mmio_write_device_config_8,
145 	virtio_mmio_read_queue_size,
146 	virtio_mmio_setup_queue,
147 	virtio_mmio_set_status,
148 	virtio_mmio_negotiate_features,
149 	virtio_mmio_intr,
150 };
151 
152 uint16_t
153 virtio_mmio_read_queue_size(struct virtio_softc *vsc, uint16_t idx)
154 {
155 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
156 	bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_SEL, idx);
157 	return bus_space_read_4(sc->sc_iot, sc->sc_ioh,
158 	    VIRTIO_MMIO_QUEUE_NUM_MAX);
159 }
160 
161 void
162 virtio_mmio_setup_queue(struct virtio_softc *vsc, struct virtqueue *vq,
163     uint64_t addr)
164 {
165 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
166 	bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_SEL,
167 	    vq->vq_index);
168 	bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_NUM,
169 	    bus_space_read_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_NUM_MAX));
170 	if (sc->sc_version == 1) {
171 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
172 		    VIRTIO_MMIO_QUEUE_ALIGN, PAGE_SIZE);
173 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
174 		    VIRTIO_MMIO_QUEUE_PFN, addr / VIRTIO_PAGE_SIZE);
175 	} else {
176 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
177 		    VIRTIO_MMIO_QUEUE_DESC_LOW, addr);
178 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
179 		    VIRTIO_MMIO_QUEUE_DESC_HIGH, addr >> 32);
180 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
181 		    VIRTIO_MMIO_QUEUE_AVAIL_LOW,
182 		    addr + vq->vq_availoffset);
183 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
184 		    VIRTIO_MMIO_QUEUE_AVAIL_HIGH,
185 		    (addr + vq->vq_availoffset) >> 32);
186 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
187 		    VIRTIO_MMIO_QUEUE_USED_LOW,
188 		    addr + vq->vq_usedoffset);
189 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
190 		    VIRTIO_MMIO_QUEUE_USED_HIGH,
191 		    (addr + vq->vq_usedoffset) >> 32);
192 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
193 		    VIRTIO_MMIO_QUEUE_READY, 1);
194 	}
195 }
196 
197 void
198 virtio_mmio_set_status(struct virtio_softc *vsc, int status)
199 {
200 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
201 	int old = 0;
202 
203 	if (status == 0) {
204 		bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_STATUS,
205 		    0);
206 		while (bus_space_read_4(sc->sc_iot, sc->sc_ioh,
207 		    VIRTIO_MMIO_STATUS) != 0) {
208 			CPU_BUSY_CYCLE();
209 		}
210 	} else  {
211 		old = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
212 		    VIRTIO_MMIO_STATUS);
213 		bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_STATUS,
214 		    status|old);
215 	}
216 }
217 
218 int
219 virtio_mmio_match(struct device *parent, void *cfdata, void *aux)
220 {
221 	struct fdt_attach_args *faa = aux;
222 
223 	return OF_is_compatible(faa->fa_node, "virtio,mmio");
224 }
225 
226 void
227 virtio_mmio_attach(struct device *parent, struct device *self, void *aux)
228 {
229 	struct fdt_attach_args *faa = aux;
230 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)self;
231 	struct virtio_softc *vsc = &sc->sc_sc;
232 	uint32_t id, magic;
233 
234 	if (faa->fa_nreg < 1) {
235 		printf(": no register data\n");
236 		return;
237 	}
238 
239 	sc->sc_iosize = faa->fa_reg[0].size;
240 	sc->sc_iot = faa->fa_iot;
241 	sc->sc_dmat = faa->fa_dmat;
242 	if (bus_space_map(sc->sc_iot, faa->fa_reg[0].addr, faa->fa_reg[0].size,
243 	    0, &sc->sc_ioh))
244 		panic("%s: bus_space_map failed!", __func__);
245 
246 	magic = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
247 	    VIRTIO_MMIO_MAGIC_VALUE);
248 	if (magic != VIRTIO_MMIO_MAGIC) {
249 		printf(": wrong magic value 0x%08x; giving up\n", magic);
250 		return;
251 	}
252 
253 	sc->sc_version = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
254 	    VIRTIO_MMIO_VERSION);
255 	if (sc->sc_version < 1 || sc->sc_version > 2) {
256 		printf(": unknown version 0x%02x; giving up\n", sc->sc_version);
257 		return;
258 	}
259 
260 	id = bus_space_read_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_DEVICE_ID);
261 	printf(": Virtio %s Device", virtio_device_string(id));
262 
263 	if (sc->sc_version == 1)
264 		bus_space_write_4(sc->sc_iot, sc->sc_ioh,
265 		    VIRTIO_MMIO_GUEST_PAGE_SIZE, PAGE_SIZE);
266 
267 	printf("\n");
268 
269 	/* No device connected. */
270 	if (id == 0)
271 		return;
272 
273 	vsc->sc_ops = &virtio_mmio_ops;
274 	vsc->sc_dmat = sc->sc_dmat;
275 	sc->sc_config_offset = VIRTIO_MMIO_CONFIG;
276 
277 	virtio_device_reset(vsc);
278 	virtio_mmio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_ACK);
279 	virtio_mmio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_DRIVER);
280 
281 	/* XXX: use softc as aux... */
282 	vsc->sc_childdevid = id;
283 	vsc->sc_child = NULL;
284 	config_found(self, sc, NULL);
285 	if (vsc->sc_child == NULL) {
286 		printf("%s: no matching child driver; not configured\n",
287 		    vsc->sc_dev.dv_xname);
288 		goto fail_1;
289 	}
290 	if (vsc->sc_child == VIRTIO_CHILD_ERROR) {
291 		printf("%s: virtio configuration failed\n",
292 		    vsc->sc_dev.dv_xname);
293 		goto fail_1;
294 	}
295 
296 	sc->sc_ih = fdt_intr_establish(faa->fa_node, vsc->sc_ipl,
297 	    virtio_mmio_intr, sc, vsc->sc_dev.dv_xname);
298 	if (sc->sc_ih == NULL) {
299 		printf("%s: couldn't establish interrupt\n",
300 		    vsc->sc_dev.dv_xname);
301 		goto fail_2;
302 	}
303 
304 	return;
305 
306 fail_2:
307 	config_detach(vsc->sc_child, 0);
308 fail_1:
309 	/* no mmio_mapreg_unmap() or mmio_intr_unmap() */
310 	virtio_set_status(vsc, VIRTIO_CONFIG_DEVICE_STATUS_FAILED);
311 }
312 
313 int
314 virtio_mmio_detach(struct device *self, int flags)
315 {
316 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)self;
317 	struct virtio_softc *vsc = &sc->sc_sc;
318 	int r;
319 
320 	if (vsc->sc_child != 0 && vsc->sc_child != VIRTIO_CHILD_ERROR) {
321 		r = config_detach(vsc->sc_child, flags);
322 		if (r)
323 			return r;
324 	}
325 	KASSERT(vsc->sc_child == 0 || vsc->sc_child == VIRTIO_CHILD_ERROR);
326 	KASSERT(vsc->sc_vqs == 0);
327 	fdt_intr_disestablish(sc->sc_ih);
328 	sc->sc_ih = 0;
329 	if (sc->sc_iosize)
330 		bus_space_unmap(sc->sc_iot, sc->sc_ioh, sc->sc_iosize);
331 	sc->sc_iosize = 0;
332 
333 	return 0;
334 }
335 
336 /*
337  * Feature negotiation.
338  * Prints available / negotiated features if guest_feature_names != NULL and
339  * VIRTIO_DEBUG is 1
340  */
341 int
342 virtio_mmio_negotiate_features(struct virtio_softc *vsc,
343     const struct virtio_feature_name *guest_feature_names)
344 {
345 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
346 	uint64_t host, neg;
347 
348 	vsc->sc_active_features = 0;
349 
350 	/*
351 	 * We enable indirect descriptors by default. They can be switched
352 	 * off by setting bit 1 in the driver flags, see config(8).
353 	 */
354 	if (!(vsc->sc_dev.dv_cfdata->cf_flags & VIRTIO_CF_NO_INDIRECT) &&
355 	    !(vsc->sc_child->dv_cfdata->cf_flags & VIRTIO_CF_NO_INDIRECT)) {
356 		vsc->sc_driver_features |= VIRTIO_F_RING_INDIRECT_DESC;
357 	} else if (guest_feature_names != NULL) {
358 		printf("RingIndirectDesc disabled by UKC\n");
359 	}
360 	/*
361 	 * The driver must add VIRTIO_F_RING_EVENT_IDX if it supports it.
362 	 * If it did, check if it is disabled by bit 2 in the driver flags.
363 	 */
364 	if ((vsc->sc_driver_features & VIRTIO_F_RING_EVENT_IDX) &&
365 	    ((vsc->sc_dev.dv_cfdata->cf_flags & VIRTIO_CF_NO_EVENT_IDX) ||
366 	    (vsc->sc_child->dv_cfdata->cf_flags & VIRTIO_CF_NO_EVENT_IDX))) {
367 		if (guest_feature_names != NULL)
368 			printf(" RingEventIdx disabled by UKC");
369 		vsc->sc_driver_features &= ~(VIRTIO_F_RING_EVENT_IDX);
370 	}
371 
372 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
373 	    VIRTIO_MMIO_HOST_FEATURES_SEL, 0);
374 	host = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
375 				VIRTIO_MMIO_HOST_FEATURES);
376 	neg = host & vsc->sc_driver_features;
377 #if VIRTIO_DEBUG
378 	if (guest_feature_names)
379 		virtio_log_features(host, neg, guest_feature_names);
380 #endif
381 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
382 	    VIRTIO_MMIO_GUEST_FEATURES_SEL, 0);
383 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
384 			  VIRTIO_MMIO_GUEST_FEATURES, neg);
385 	vsc->sc_active_features = neg;
386 	if (neg & VIRTIO_F_RING_INDIRECT_DESC)
387 		vsc->sc_indirect = 1;
388 	else
389 		vsc->sc_indirect = 0;
390 
391 	return 0;
392 }
393 
394 /*
395  * Device configuration registers.
396  */
397 uint8_t
398 virtio_mmio_read_device_config_1(struct virtio_softc *vsc, int index)
399 {
400 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
401 	return bus_space_read_1(sc->sc_iot, sc->sc_ioh,
402 				sc->sc_config_offset + index);
403 }
404 
405 uint16_t
406 virtio_mmio_read_device_config_2(struct virtio_softc *vsc, int index)
407 {
408 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
409 	return bus_space_read_2(sc->sc_iot, sc->sc_ioh,
410 				sc->sc_config_offset + index);
411 }
412 
413 uint32_t
414 virtio_mmio_read_device_config_4(struct virtio_softc *vsc, int index)
415 {
416 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
417 	return bus_space_read_4(sc->sc_iot, sc->sc_ioh,
418 				sc->sc_config_offset + index);
419 }
420 
421 uint64_t
422 virtio_mmio_read_device_config_8(struct virtio_softc *vsc, int index)
423 {
424 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
425 	uint64_t r;
426 
427 	r = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
428 			     sc->sc_config_offset + index + sizeof(uint32_t));
429 	r <<= 32;
430 	r += bus_space_read_4(sc->sc_iot, sc->sc_ioh,
431 			      sc->sc_config_offset + index);
432 	return r;
433 }
434 
435 void
436 virtio_mmio_write_device_config_1(struct virtio_softc *vsc,
437 			     int index, uint8_t value)
438 {
439 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
440 	bus_space_write_1(sc->sc_iot, sc->sc_ioh,
441 			  sc->sc_config_offset + index, value);
442 }
443 
444 void
445 virtio_mmio_write_device_config_2(struct virtio_softc *vsc,
446 			     int index, uint16_t value)
447 {
448 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
449 	bus_space_write_2(sc->sc_iot, sc->sc_ioh,
450 			  sc->sc_config_offset + index, value);
451 }
452 
453 void
454 virtio_mmio_write_device_config_4(struct virtio_softc *vsc,
455 			     int index, uint32_t value)
456 {
457 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
458 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
459 			  sc->sc_config_offset + index, value);
460 }
461 
462 void
463 virtio_mmio_write_device_config_8(struct virtio_softc *vsc,
464 			     int index, uint64_t value)
465 {
466 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
467 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
468 			  sc->sc_config_offset + index,
469 			  value & 0xffffffff);
470 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
471 			  sc->sc_config_offset + index + sizeof(uint32_t),
472 			  value >> 32);
473 }
474 
475 /*
476  * Interrupt handler.
477  */
478 int
479 virtio_mmio_intr(void *arg)
480 {
481 	struct virtio_mmio_softc *sc = arg;
482 	struct virtio_softc *vsc = &sc->sc_sc;
483 	int isr, r = 0;
484 
485 	/* check and ack the interrupt */
486 	isr = bus_space_read_4(sc->sc_iot, sc->sc_ioh,
487 			       VIRTIO_MMIO_INTERRUPT_STATUS);
488 	bus_space_write_4(sc->sc_iot, sc->sc_ioh,
489 			  VIRTIO_MMIO_INTERRUPT_ACK, isr);
490 	if ((isr & VIRTIO_MMIO_INT_CONFIG) &&
491 	    (vsc->sc_config_change != NULL))
492 		r = (vsc->sc_config_change)(vsc);
493 	if ((isr & VIRTIO_MMIO_INT_VRING))
494 		r |= virtio_check_vqs(vsc);
495 
496 	return r;
497 }
498 
499 void
500 virtio_mmio_kick(struct virtio_softc *vsc, uint16_t idx)
501 {
502 	struct virtio_mmio_softc *sc = (struct virtio_mmio_softc *)vsc;
503 	bus_space_write_4(sc->sc_iot, sc->sc_ioh, VIRTIO_MMIO_QUEUE_NOTIFY,
504 	    idx);
505 }
506