aboutsummaryrefslogtreecommitdiff
path: root/drivers/rpmsg/virtio_rpmsg_bus.c
blob: 4db9cf8754a0e211ba4cc1900540e99add01b46b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
/*
 * Virtio-based remote processor messaging bus
 *
 * Copyright (C) 2011 Texas Instruments, Inc.
 * Copyright (C) 2011 Google, Inc.
 *
 * Ohad Ben-Cohen <ohad@wizery.com>
 * Brian Swetland <swetland@google.com>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#define pr_fmt(fmt) "%s: " fmt, __func__

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/virtio.h>
#include <linux/virtio_ids.h>
#include <linux/virtio_config.h>
#include <linux/scatterlist.h>
#include <linux/dma-mapping.h>
#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/jiffies.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/rpmsg.h>
#include <linux/mutex.h>

/**
 * struct virtproc_info - virtual remote processor state
 * @vdev:	the virtio device
 * @rvq:	rx virtqueue
 * @svq:	tx virtqueue
 * @rbufs:	kernel address of rx buffers
 * @sbufs:	kernel address of tx buffers
 * @last_sbuf:	index of last tx buffer used
 * @bufs_dma:	dma base addr of the buffers
 * @tx_lock:	protects svq, sbufs and sleepers, to allow concurrent senders.
 *		sending a message might require waking up a dozing remote
 *		processor, which involves sleeping, hence the mutex.
 * @endpoints:	idr of local endpoints, allows fast retrieval
 * @endpoints_lock: lock of the endpoints set
 * @sendq:	wait queue of sending contexts waiting for a tx buffers
 * @sleepers:	number of senders that are waiting for a tx buffer
 * @ns_ept:	the bus's name service endpoint
 *
 * This structure stores the rpmsg state of a given virtio remote processor
 * device (there might be several virtio proc devices for each physical
 * remote processor).
 */
struct virtproc_info {
	struct virtio_device *vdev;
	struct virtqueue *rvq, *svq;
	void *rbufs, *sbufs;
	int last_sbuf;
	dma_addr_t bufs_dma;
	struct mutex tx_lock;
	struct idr endpoints;
	struct mutex endpoints_lock;
	wait_queue_head_t sendq;
	atomic_t sleepers;
	struct rpmsg_endpoint *ns_ept;
};

/**
 * struct rpmsg_channel_info - internal channel info representation
 * @name: name of service
 * @src: local address
 * @dst: destination address
 */
struct rpmsg_channel_info {
	char name[RPMSG_NAME_SIZE];
	u32 src;
	u32 dst;
};

#define to_rpmsg_channel(d) container_of(d, struct rpmsg_channel, dev)
#define to_rpmsg_driver(d) container_of(d, struct rpmsg_driver, drv)

/*
 * We're allocating 512 buffers of 512 bytes for communications, and then
 * using the first 256 buffers for RX, and the last 256 buffers for TX.
 *
 * Each buffer will have 16 bytes for the msg header and 496 bytes for
 * the payload.
 *
 * This will require a total space of 256KB for the buffers.
 *
 * We might also want to add support for user-provided buffers in time.
 * This will allow bigger buffer size flexibility, and can also be used
 * to achieve zero-copy messaging.
 *
 * Note that these numbers are purely a decision of this driver - we
 * can change this without changing anything in the firmware of the remote
 * processor.
 */
#define RPMSG_NUM_BUFS		(512)
#define RPMSG_BUF_SIZE		(512)
#define RPMSG_TOTAL_BUF_SPACE	(RPMSG_NUM_BUFS * RPMSG_BUF_SIZE)

/*
 * Local addresses are dynamically allocated on-demand.
 * We do not dynamically assign addresses from the low 1024 range,
 * in order to reserve that address range for predefined services.
 */
#define RPMSG_RESERVED_ADDRESSES	(1024)

/* Address 53 is reserved for advertising remote services */
#define RPMSG_NS_ADDR			(53)

/* sysfs show configuration fields */
#define rpmsg_show_attr(field, path, format_string)			\
static ssize_t								\
field##_show(struct device *dev,					\
			struct device_attribute *attr, char *buf)	\
{									\
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);		\
									\
	return sprintf(buf, format_string, rpdev->path);		\
}

/* for more info, see Documentation/ABI/testing/sysfs-bus-rpmsg */
rpmsg_show_attr(name, id.name, "%s\n");
rpmsg_show_attr(src, src, "0x%x\n");
rpmsg_show_attr(dst, dst, "0x%x\n");
rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");

/*
 * Unique (and free running) index for rpmsg devices.
 *
 * Yeah, we're not recycling those numbers (yet?). will be easy
 * to change if/when we want to.
 */
static unsigned int rpmsg_dev_index;

static ssize_t modalias_show(struct device *dev,
			     struct device_attribute *attr, char *buf)
{
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

	return sprintf(buf, RPMSG_DEVICE_MODALIAS_FMT "\n", rpdev->id.name);
}

static struct device_attribute rpmsg_dev_attrs[] = {
	__ATTR_RO(name),
	__ATTR_RO(modalias),
	__ATTR_RO(dst),
	__ATTR_RO(src),
	__ATTR_RO(announce),
	__ATTR_NULL
};

/* rpmsg devices and drivers are matched using the service name */
static inline int rpmsg_id_match(const struct rpmsg_channel *rpdev,
				  const struct rpmsg_device_id *id)
{
	return strncmp(id->name, rpdev->id.name, RPMSG_NAME_SIZE) == 0;
}

/* match rpmsg channel and rpmsg driver */
static int rpmsg_dev_match(struct device *dev, struct device_driver *drv)
{
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
	struct rpmsg_driver *rpdrv = to_rpmsg_driver(drv);
	const struct rpmsg_device_id *ids = rpdrv->id_table;
	unsigned int i;

	for (i = 0; ids[i].name[0]; i++)
		if (rpmsg_id_match(rpdev, &ids[i]))
			return 1;

	return 0;
}

static int rpmsg_uevent(struct device *dev, struct kobj_uevent_env *env)
{
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

	return add_uevent_var(env, "MODALIAS=" RPMSG_DEVICE_MODALIAS_FMT,
					rpdev->id.name);
}

/* for more info, see below documentation of rpmsg_create_ept() */
static struct rpmsg_endpoint *__rpmsg_create_ept(struct virtproc_info *vrp,
		struct rpmsg_channel *rpdev, rpmsg_rx_cb_t cb,
		void *priv, u32 addr)
{
	int err, tmpaddr, request;
	struct rpmsg_endpoint *ept;
	struct device *dev = rpdev ? &rpdev->dev : &vrp->vdev->dev;

	if (!idr_pre_get(&vrp->endpoints, GFP_KERNEL))
		return NULL;

	ept = kzalloc(sizeof(*ept), GFP_KERNEL);
	if (!ept) {
		dev_err(dev, "failed to kzalloc a new ept\n");
		return NULL;
	}

	ept->rpdev = rpdev;
	ept->cb = cb;
	ept->priv = priv;

	/* do we need to allocate a local address ? */
	request = addr == RPMSG_ADDR_ANY ? RPMSG_RESERVED_ADDRESSES : addr;

	mutex_lock(&vrp->endpoints_lock);

	/* bind the endpoint to an rpmsg address (and allocate one if needed) */
	err = idr_get_new_above(&vrp->endpoints, ept, request, &tmpaddr);
	if (err) {
		dev_err(dev, "idr_get_new_above failed: %d\n", err);
		goto free_ept;
	}

	/* make sure the user's address request is fulfilled, if relevant */
	if (addr != RPMSG_ADDR_ANY && tmpaddr != addr) {
		dev_err(dev, "address 0x%x already in use\n", addr);
		goto rem_idr;
	}

	ept->addr = tmpaddr;

	mutex_unlock(&vrp->endpoints_lock);

	return ept;

rem_idr:
	idr_remove(&vrp->endpoints, request);
free_ept:
	mutex_unlock(&vrp->endpoints_lock);
	kfree(ept);
	return NULL;
}

/**
 * rpmsg_create_ept() - create a new rpmsg_endpoint
 * @rpdev: rpmsg channel device
 * @cb: rx callback handler
 * @priv: private data for the driver's use
 * @addr: local rpmsg address to bind with @cb
 *
 * Every rpmsg address in the system is bound to an rx callback (so when
 * inbound messages arrive, they are dispatched by the rpmsg bus using the
 * appropriate callback handler) by means of an rpmsg_endpoint struct.
 *
 * This function allows drivers to create such an endpoint, and by that,
 * bind a callback, and possibly some private data too, to an rpmsg address
 * (either one that is known in advance, or one that will be dynamically
 * assigned for them).
 *
 * Simple rpmsg drivers need not call rpmsg_create_ept, because an endpoint
 * is already created for them when they are probed by the rpmsg bus
 * (using the rx callback provided when they registered to the rpmsg bus).
 *
 * So things should just work for simple drivers: they already have an
 * endpoint, their rx callback is bound to their rpmsg address, and when
 * relevant inbound messages arrive (i.e. messages which their dst address
 * equals to the src address of their rpmsg channel), the driver's handler
 * is invoked to process it.
 *
 * That said, more complicated drivers might do need to allocate
 * additional rpmsg addresses, and bind them to different rx callbacks.
 * To accomplish that, those drivers need to call this function.
 *
 * Drivers should provide their @rpdev channel (so the new endpoint would belong
 * to the same remote processor their channel belongs to), an rx callback
 * function, an optional private data (which is provided back when the
 * rx callback is invoked), and an address they want to bind with the
 * callback. If @addr is RPMSG_ADDR_ANY, then rpmsg_create_ept will
 * dynamically assign them an available rpmsg address (drivers should have
 * a very good reason why not to always use RPMSG_ADDR_ANY here).
 *
 * Returns a pointer to the endpoint on success, or NULL on error.
 */
struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_channel *rpdev,
				rpmsg_rx_cb_t cb, void *priv, u32 addr)
{
	return __rpmsg_create_ept(rpdev->vrp, rpdev, cb, priv, addr);
}
EXPORT_SYMBOL(rpmsg_create_ept);

/**
 * __rpmsg_destroy_ept() - destroy an existing rpmsg endpoint
 * @vrp: virtproc which owns this ept
 * @ept: endpoing to destroy
 *
 * An internal function which destroy an ept without assuming it is
 * bound to an rpmsg channel. This is needed for handling the internal
 * name service endpoint, which isn't bound to an rpmsg channel.
 * See also __rpmsg_create_ept().
 */
static void
__rpmsg_destroy_ept(struct virtproc_info *vrp, struct rpmsg_endpoint *ept)
{
	mutex_lock(&vrp->endpoints_lock);
	idr_remove(&vrp->endpoints, ept->addr);
	mutex_unlock(&vrp->endpoints_lock);

	kfree(ept);
}

/**
 * rpmsg_destroy_ept() - destroy an existing rpmsg endpoint
 * @ept: endpoing to destroy
 *
 * Should be used by drivers to destroy an rpmsg endpoint previously
 * created with rpmsg_create_ept().
 */
void rpmsg_destroy_ept(struct rpmsg_endpoint *ept)
{
	__rpmsg_destroy_ept(ept->rpdev->vrp, ept);
}
EXPORT_SYMBOL(rpmsg_destroy_ept);

/*
 * when an rpmsg driver is probed with a channel, we seamlessly create
 * it an endpoint, binding its rx callback to a unique local rpmsg
 * address.
 *
 * if we need to, we also announce about this channel to the remote
 * processor (needed in case the driver is exposing an rpmsg service).
 */
static int rpmsg_dev_probe(struct device *dev)
{
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
	struct rpmsg_driver *rpdrv = to_rpmsg_driver(rpdev->dev.driver);
	struct virtproc_info *vrp = rpdev->vrp;
	struct rpmsg_endpoint *ept;
	int err;

	ept = rpmsg_create_ept(rpdev, rpdrv->callback, NULL, rpdev->src);
	if (!ept) {
		dev_err(dev, "failed to create endpoint\n");
		err = -ENOMEM;
		goto out;
	}

	rpdev->ept = ept;
	rpdev->src = ept->addr;

	err = rpdrv->probe(rpdev);
	if (err) {
		dev_err(dev, "%s: failed: %d\n", __func__, err);
		rpmsg_destroy_ept(ept);
		goto out;
	}

	/* need to tell remote processor's name service about this channel ? */
	if (rpdev->announce &&
			virtio_has_feature(vrp->vdev, VIRTIO_RPMSG_F_NS)) {
		struct rpmsg_ns_msg nsm;

		strncpy(nsm.name, rpdev->id.name, RPMSG_NAME_SIZE);
		nsm.addr = rpdev->src;
		nsm.flags = RPMSG_NS_CREATE;

		err = rpmsg_sendto(rpdev, &nsm, sizeof(nsm), RPMSG_NS_ADDR);
		if (err)
			dev_err(dev, "failed to announce service %d\n", err);
	}

out:
	return err;
}

static int rpmsg_dev_remove(struct device *dev)
{
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
	struct rpmsg_driver *rpdrv = to_rpmsg_driver(rpdev->dev.driver);
	struct virtproc_info *vrp = rpdev->vrp;
	int err = 0;

	/* tell remote processor's name service we're removing this channel */
	if (rpdev->announce &&
			virtio_has_feature(vrp->vdev, VIRTIO_RPMSG_F_NS)) {
		struct rpmsg_ns_msg nsm;

		strncpy(nsm.name, rpdev->id.name, RPMSG_NAME_SIZE);
		nsm.addr = rpdev->src;
		nsm.flags = RPMSG_NS_DESTROY;

		err = rpmsg_sendto(rpdev, &nsm, sizeof(nsm), RPMSG_NS_ADDR);
		if (err)
			dev_err(dev, "failed to announce service %d\n", err);
	}

	rpdrv->remove(rpdev);

	rpmsg_destroy_ept(rpdev->ept);

	return err;
}

static struct bus_type rpmsg_bus = {
	.name		= "rpmsg",
	.match		= rpmsg_dev_match,
	.dev_attrs	= rpmsg_dev_attrs,
	.uevent		= rpmsg_uevent,
	.probe		= rpmsg_dev_probe,
	.remove		= rpmsg_dev_remove,
};

/**
 * register_rpmsg_driver() - register an rpmsg driver with the rpmsg bus
 * @rpdrv: pointer to a struct rpmsg_driver
 *
 * Returns 0 on success, and an appropriate error value on failure.
 */
int register_rpmsg_driver(struct rpmsg_driver *rpdrv)
{
	rpdrv->drv.bus = &rpmsg_bus;
	return driver_register(&rpdrv->drv);
}
EXPORT_SYMBOL(register_rpmsg_driver);

/**
 * unregister_rpmsg_driver() - unregister an rpmsg driver from the rpmsg bus
 * @rpdrv: pointer to a struct rpmsg_driver
 *
 * Returns 0 on success, and an appropriate error value on failure.
 */
void unregister_rpmsg_driver(struct rpmsg_driver *rpdrv)
{
	driver_unregister(&rpdrv->drv);
}
EXPORT_SYMBOL(unregister_rpmsg_driver);

static void rpmsg_release_device(struct device *dev)
{
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

	kfree(rpdev);
}

/*
 * match an rpmsg channel with a channel info struct.
 * this is used to make sure we're not creating rpmsg devices for channels
 * that already exist.
 */
static int rpmsg_channel_match(struct device *dev, void *data)
{
	struct rpmsg_channel_info *chinfo = data;
	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

	if (chinfo->src != RPMSG_ADDR_ANY && chinfo->src != rpdev->src)
		return 0;

	if (chinfo->dst != RPMSG_ADDR_ANY && chinfo->dst != rpdev->dst)
		return 0;

	if (strncmp(chinfo->name, rpdev->id.name, RPMSG_NAME_SIZE))
		return 0;

	/* found a match ! */
	return 1;
}

/*
 * create an rpmsg channel using its name and address info.
 * this function will be used to create both static and dynamic
 * channels.
 */
static struct rpmsg_channel *rpmsg_create_channel(struct virtproc_info *vrp,
				struct rpmsg_channel_info *chinfo)
{
	struct rpmsg_channel *rpdev;
	struct device *tmp, *dev = &vrp->vdev->dev;
	int ret;

	/* make sure a similar channel doesn't already exist */
	tmp = device_find_child(dev, chinfo, rpmsg_channel_match);
	if (tmp) {
		/* decrement the matched device's refcount back */
		put_device(tmp);
		dev_err(dev, "channel %s:%x:%x already exist\n",
				chinfo->name, chinfo->src, chinfo->dst);
		return NULL;
	}

	rpdev = kzalloc(sizeof(struct rpmsg_channel), GFP_KERNEL);
	if (!rpdev) {
		pr_err("kzalloc failed\n");
		return NULL;
	}

	rpdev->vrp = vrp;
	rpdev->src = chinfo->src;
	rpdev->dst = chinfo->dst;

	/*
	 * rpmsg server channels has predefined local address (for now),
	 * and their existence needs to be announced remotely
	 */
	rpdev->announce = rpdev->src != RPMSG_ADDR_ANY ? true : false;

	strncpy(rpdev->id.name, chinfo->name, RPMSG_NAME_SIZE);

	/* very simple device indexing plumbing which is enough for now */
	dev_set_name(&rpdev->dev, "rpmsg%d", rpmsg_dev_index++);

	rpdev->dev.parent = &vrp->vdev->dev;
	rpdev->dev.bus = &rpmsg_bus;
	rpdev->dev.release = rpmsg_release_device;

	ret = device_register(&rpdev->dev);
	if (ret) {
		dev_err(dev, "device_register failed: %d\n", ret);
		put_device(&rpdev->dev);
		return NULL;
	}

	return rpdev;
}

/*
 * find an existing channel using its name + address properties,
 * and destroy it
 */
static int rpmsg_destroy_channel(struct virtproc_info *vrp,
					struct rpmsg_channel_info *chinfo)
{
	struct virtio_device *vdev = vrp->vdev;
	struct device *dev;

	dev = device_find_child(&vdev->dev, chinfo, rpmsg_channel_match);
	if (!dev)
		return -EINVAL;

	device_unregister(dev);

	put_device(dev);

	return 0;
}

/* super simple buffer "allocator" that is just enough for now */
static void *get_a_tx_buf(struct virtproc_info *vrp)
{
	unsigned int len;
	void *ret;

	/* support multiple concurrent senders */
	mutex_lock(&vrp->tx_lock);

	/*
	 * either pick the next unused tx buffer
	 * (half of our buffers are used for sending messages)
	 */
	if (vrp->last_sbuf < RPMSG_NUM_BUFS / 2)
		ret = vrp->sbufs + RPMSG_BUF_SIZE * vrp->last_sbuf++;
	/* or recycle a used one */
	else
		ret = virtqueue_get_buf(vrp->svq, &len);

	mutex_unlock(&vrp->tx_lock);

	return ret;
}

/**
 * rpmsg_upref_sleepers() - enable "tx-complete" interrupts, if needed
 * @vrp: virtual remote processor state
 *
 * This function is called before a sender is blocked, waiting for
 * a tx buffer to become available.
 *
 * If we already have blocking senders, this function merely increases
 * the "sleepers" reference count, and exits.
 *
 * Otherwise, if this is the first sender to block, we also enable
 * virtio's tx callbacks, so we'd be immediately notified when a tx
 * buffer is consumed (we rely on virtio's tx callback in order
 * to wake up sleeping senders as soon as a tx buffer is used by the
 * remote processor).
 */
static void rpmsg_upref_sleepers(struct virtproc_info *vrp)
{
	/* support multiple concurrent senders */
	mutex_lock(&vrp->tx_lock);

	/* are we the first sleeping context waiting for tx buffers ? */
	if (atomic_inc_return(&vrp->sleepers) == 1)
		/* enable "tx-complete" interrupts before dozing off */
		virtqueue_enable_cb(vrp->svq);

	mutex_unlock(&vrp->tx_lock);
}

/**
 * rpmsg_downref_sleepers() - disable "tx-complete" interrupts, if needed
 * @vrp: virtual remote processor state
 *
 * This function is called after a sender, that waited for a tx buffer
 * to become available, is unblocked.
 *
 * If we still have blocking senders, this function merely decreases
 * the "sleepers" reference count, and exits.
 *
 * Otherwise, if there are no more blocking senders, we also disable
 * virtio's tx callbacks, to avoid the overhead incurred with handling
 * those (now redundant) interrupts.
 */
static void rpmsg_downref_sleepers(struct virtproc_info *vrp)
{
	/* support multiple concurrent senders */
	mutex_lock(&vrp->tx_lock);

	/* are we the last sleeping context waiting for tx buffers ? */
	if (atomic_dec_and_test(&vrp->sleepers))
		/* disable "tx-complete" interrupts */
		virtqueue_disable_cb(vrp->svq);

	mutex_unlock(&vrp->tx_lock);
}

/**
 * rpmsg_send_offchannel_raw() - send a message across to the remote processor
 * @rpdev: the rpmsg channel
 * @src: source address
 * @dst: destination address
 * @data: payload of message
 * @len: length of payload
 * @wait: indicates whether caller should block in case no TX buffers available
 *
 * This function is the base implementation for all of the rpmsg sending API.
 *
 * It will send @data of length @len to @dst, and say it's from @src. The
 * message will be sent to the remote processor which the @rpdev channel
 * belongs to.
 *
 * The message is sent using one of the TX buffers that are available for
 * communication with this remote processor.
 *
 * If @wait is true, the caller will be blocked until either a TX buffer is
 * available, or 15 seconds elapses (we don't want callers to
 * sleep indefinitely due to misbehaving remote processors), and in that
 * case -ERESTARTSYS is returned. The number '15' itself was picked
 * arbitrarily; there's little point in asking drivers to provide a timeout
 * value themselves.
 *
 * Otherwise, if @wait is false, and there are no TX buffers available,
 * the function will immediately fail, and -ENOMEM will be returned.
 *
 * Normally drivers shouldn't use this function directly; instead, drivers
 * should use the appropriate rpmsg_{try}send{to, _offchannel} API
 * (see include/linux/rpmsg.h).
 *
 * Returns 0 on success and an appropriate error value on failure.
 */
int rpmsg_send_offchannel_raw(struct rpmsg_channel *rpdev, u32 src, u32 dst,
					void *data, int len, bool wait)
{
	struct virtproc_info *vrp = rpdev->vrp;
	struct device *dev = &rpdev->dev;
	struct scatterlist sg;
	struct rpmsg_hdr *msg;
	int err;

	/* bcasting isn't allowed */
	if (src == RPMSG_ADDR_ANY || dst == RPMSG_ADDR_ANY) {
		dev_err(dev, "invalid addr (src 0x%x, dst 0x%x)\n", src, dst);
		return -EINVAL;
	}

	/*
	 * We currently use fixed-sized buffers, and therefore the payload
	 * length is limited.
	 *
	 * One of the possible improvements here is either to support
	 * user-provided buffers (and then we can also support zero-copy
	 * messaging), or to improve the buffer allocator, to support
	 * variable-length buffer sizes.
	 */
	if (len > RPMSG_BUF_SIZE - sizeof(struct rpmsg_hdr)) {
		dev_err(dev, "message is too big (%d)\n", len);
		return -EMSGSIZE;
	}

	/* grab a buffer */
	msg = get_a_tx_buf(vrp);
	if (!msg && !wait)
		return -ENOMEM;

	/* no free buffer ? wait for one (but bail after 15 seconds) */
	while (!msg) {
		/* enable "tx-complete" interrupts, if not already enabled */
		rpmsg_upref_sleepers(vrp);

		/*
		 * sleep until a free buffer is available or 15 secs elapse.
		 * the timeout period is not configurable because there's
		 * little point in asking drivers to specify that.
		 * if later this happens to be required, it'd be easy to add.
		 */
		err = wait_event_interruptible_timeout(vrp->sendq,
					(msg = get_a_tx_buf(vrp)),
					msecs_to_jiffies(15000));

		/* disable "tx-complete" interrupts if we're the last sleeper */
		rpmsg_downref_sleepers(vrp);

		/* timeout ? */
		if (!err) {
			dev_err(dev, "timeout waiting for a tx buffer\n");
			return -ERESTARTSYS;
		}
	}

	msg->len = len;
	msg->flags = 0;
	msg->src = src;
	msg->dst = dst;
	msg->reserved = 0;
	memcpy(msg->data, data, len);

	dev_dbg(dev, "TX From 0x%x, To 0x%x, Len %d, Flags %d, Reserved %d\n",
					msg->src, msg->dst, msg->len,
					msg->flags, msg->reserved);
	print_hex_dump(KERN_DEBUG, "rpmsg_virtio TX: ", DUMP_PREFIX_NONE, 16, 1,
					msg, sizeof(*msg) + msg->len, true);

	sg_init_one(&sg, msg, sizeof(*msg) + len);

	mutex_lock(&vrp->tx_lock);

	/* add message to the remote processor's virtqueue */
	err = virtqueue_add_buf(vrp->svq, &sg, 1, 0, msg, GFP_KERNEL);
	if (err < 0) {
		/*
		 * need to reclaim the buffer here, otherwise it's lost
		 * (memory won't leak, but rpmsg won't use it again for TX).
		 * this will wait for a buffer management overhaul.
		 */
		dev_err(dev, "virtqueue_add_buf failed: %d\n", err);
		goto out;
	}

	/* tell the remote processor it has a pending message to read */
	virtqueue_kick(vrp->svq);

	err = 0;
out:
	mutex_unlock(&vrp->tx_lock);
	return err;
}
EXPORT_SYMBOL(rpmsg_send_offchannel_raw);

/* called when an rx buffer is used, and it's time to digest a message */
static void rpmsg_recv_done(struct virtqueue *rvq)
{
	struct rpmsg_hdr *msg;
	unsigned int len;
	struct rpmsg_endpoint *ept;
	struct scatterlist sg;
	struct virtproc_info *vrp = rvq->vdev->priv;
	struct device *dev = &rvq->vdev->dev;
	int err;

	msg = virtqueue_get_buf(rvq, &len);
	if (!msg) {
		dev_err(dev, "uhm, incoming signal, but no used buffer ?\n");
		return;
	}

	dev_dbg(dev, "From: 0x%x, To: 0x%x, Len: %d, Flags: %d, Reserved: %d\n",
					msg->src, msg->dst, msg->len,
					msg->flags, msg->reserved);
	print_hex_dump(KERN_DEBUG, "rpmsg_virtio RX: ", DUMP_PREFIX_NONE, 16, 1,
					msg, sizeof(*msg) + msg->len, true);

	/* use the dst addr to fetch the callback of the appropriate user */
	mutex_lock(&vrp->endpoints_lock);
	ept = idr_find(&vrp->endpoints, msg->dst);
	mutex_unlock(&vrp->endpoints_lock);

	if (ept && ept->cb)
		ept->cb(ept->rpdev, msg->data, msg->len, ept->priv, msg->src);
	else
		dev_warn(dev, "msg received with no recepient\n");

	sg_init_one(&sg, msg, sizeof(*msg) + len);

	/* add the buffer back to the remote processor's virtqueue */
	err = virtqueue_add_buf(vrp->rvq, &sg, 0, 1, msg, GFP_KERNEL);
	if (err < 0) {
		dev_err(dev, "failed to add a virtqueue buffer: %d\n", err);
		return;
	}

	/* tell the remote processor we added another available rx buffer */
	virtqueue_kick(vrp->rvq);
}

/*
 * This is invoked whenever the remote processor completed processing
 * a TX msg we just sent it, and the buffer is put back to the used ring.
 *
 * Normally, though, we suppress this "tx complete" interrupt in order to
 * avoid the incurred overhead.
 */
static void rpmsg_xmit_done(struct virtqueue *svq)
{
	struct virtproc_info *vrp = svq->vdev->priv;

	dev_dbg(&svq->vdev->dev, "%s\n", __func__);

	/* wake up potential senders that are waiting for a tx buffer */
	wake_up_interruptible(&vrp->sendq);
}

/* invoked when a name service announcement arrives */
static void rpmsg_ns_cb(struct rpmsg_channel *rpdev, void *data, int len,
							void *priv, u32 src)
{
	struct rpmsg_ns_msg *msg = data;
	struct rpmsg_channel *newch;
	struct rpmsg_channel_info chinfo;
	struct virtproc_info *vrp = priv;
	struct device *dev = &vrp->vdev->dev;
	int ret;

	print_hex_dump(KERN_DEBUG, "NS announcement: ",
			DUMP_PREFIX_NONE, 16, 1,
			data, len, true);

	if (len != sizeof(*msg)) {
		dev_err(dev, "malformed ns msg (%d)\n", len);
		return;
	}

	/*
	 * the name service ept does _not_ belong to a real rpmsg channel,
	 * and is handled by the rpmsg bus itself.
	 * for sanity reasons, make sure a valid rpdev has _not_ sneaked
	 * in somehow.
	 */
	if (rpdev) {
		dev_err(dev, "anomaly: ns ept has an rpdev handle\n");
		return;
	}

	/* don't trust the remote processor for null terminating the name */
	msg->name[RPMSG_NAME_SIZE - 1] = '\0';

	dev_info(dev, "%sing channel %s addr 0x%x\n",
			msg->flags & RPMSG_NS_DESTROY ? "destroy" : "creat",
			msg->name, msg->addr);

	strncpy(chinfo.name, msg->name, sizeof(chinfo.name));
	chinfo.src = RPMSG_ADDR_ANY;
	chinfo.dst = msg->addr;

	if (msg->flags & RPMSG_NS_DESTROY) {
		ret = rpmsg_destroy_channel(vrp, &chinfo);
		if (ret)
			dev_err(dev, "rpmsg_destroy_channel failed: %d\n", ret);
	} else {
		newch = rpmsg_create_channel(vrp, &chinfo);
		if (!newch)
			dev_err(dev, "rpmsg_create_channel failed\n");
	}
}

static int rpmsg_probe(struct virtio_device *vdev)
{
	vq_callback_t *vq_cbs[] = { rpmsg_recv_done, rpmsg_xmit_done };
	const char *names[] = { "input", "output" };
	struct virtqueue *vqs[2];
	struct virtproc_info *vrp;
	void *bufs_va;
	int err = 0, i;

	vrp = kzalloc(sizeof(*vrp), GFP_KERNEL);
	if (!vrp)
		return -ENOMEM;

	vrp->vdev = vdev;

	idr_init(&vrp->endpoints);
	mutex_init(&vrp->endpoints_lock);
	mutex_init(&vrp->tx_lock);
	init_waitqueue_head(&vrp->sendq);

	/* We expect two virtqueues, rx and tx (and in this order) */
	err = vdev->config->find_vqs(vdev, 2, vqs, vq_cbs, names);
	if (err)
		goto free_vrp;

	vrp->rvq = vqs[0];
	vrp->svq = vqs[1];

	/* allocate coherent memory for the buffers */
	bufs_va = dma_alloc_coherent(vdev->dev.parent, RPMSG_TOTAL_BUF_SPACE,
				&vrp->bufs_dma, GFP_KERNEL);
	if (!bufs_va)
		goto vqs_del;

	dev_dbg(&vdev->dev, "buffers: va %p, dma 0x%x\n", bufs_va,
						vrp->bufs_dma);

	/* half of the buffers is dedicated for RX */
	vrp->rbufs = bufs_va;

	/* and half is dedicated for TX */
	vrp->sbufs = bufs_va + RPMSG_TOTAL_BUF_SPACE / 2;

	/* set up the receive buffers */
	for (i = 0; i < RPMSG_NUM_BUFS / 2; i++) {
		struct scatterlist sg;
		void *cpu_addr = vrp->rbufs + i * RPMSG_BUF_SIZE;

		sg_init_one(&sg, cpu_addr, RPMSG_BUF_SIZE);

		err = virtqueue_add_buf(vrp->rvq, &sg, 0, 1, cpu_addr,
								GFP_KERNEL);
		WARN_ON(err < 0); /* sanity check; this can't really happen */
	}

	/* suppress "tx-complete" interrupts */
	virtqueue_disable_cb(vrp->svq);

	vdev->priv = vrp;

	/* if supported by the remote processor, enable the name service */
	if (virtio_has_feature(vdev, VIRTIO_RPMSG_F_NS)) {
		/* a dedicated endpoint handles the name service msgs */
		vrp->ns_ept = __rpmsg_create_ept(vrp, NULL, rpmsg_ns_cb,
						vrp, RPMSG_NS_ADDR);
		if (!vrp->ns_ept) {
			dev_err(&vdev->dev, "failed to create the ns ept\n");
			err = -ENOMEM;
			goto free_coherent;
		}
	}

	/* tell the remote processor it can start sending messages */
	virtqueue_kick(vrp->rvq);

	dev_info(&vdev->dev, "rpmsg host is online\n");

	return 0;

free_coherent:
	dma_free_coherent(vdev->dev.parent, RPMSG_TOTAL_BUF_SPACE, bufs_va,
					vrp->bufs_dma);
vqs_del:
	vdev->config->del_vqs(vrp->vdev);
free_vrp:
	kfree(vrp);
	return err;
}

static int rpmsg_remove_device(struct device *dev, void *data)
{
	device_unregister(dev);

	return 0;
}

static void __devexit rpmsg_remove(struct virtio_device *vdev)
{
	struct virtproc_info *vrp = vdev->priv;
	int ret;

	vdev->config->reset(vdev);

	ret = device_for_each_child(&vdev->dev, NULL, rpmsg_remove_device);
	if (ret)
		dev_warn(&vdev->dev, "can't remove rpmsg device: %d\n", ret);

	if (vrp->ns_ept)
		__rpmsg_destroy_ept(vrp, vrp->ns_ept);

	idr_remove_all(&vrp->endpoints);
	idr_destroy(&vrp->endpoints);

	vdev->config->del_vqs(vrp->vdev);

	dma_free_coherent(vdev->dev.parent, RPMSG_TOTAL_BUF_SPACE,
					vrp->rbufs, vrp->bufs_dma);

	kfree(vrp);
}

static struct virtio_device_id id_table[] = {
	{ VIRTIO_ID_RPMSG, VIRTIO_DEV_ANY_ID },
	{ 0 },
};

static unsigned int features[] = {
	VIRTIO_RPMSG_F_NS,
};

static struct virtio_driver virtio_ipc_driver = {
	.feature_table	= features,
	.feature_table_size = ARRAY_SIZE(features),
	.driver.name	= KBUILD_MODNAME,
	.driver.owner	= THIS_MODULE,
	.id_table	= id_table,
	.probe		= rpmsg_probe,
	.remove		= __devexit_p(rpmsg_remove),
};

static int __init rpmsg_init(void)
{
	int ret;

	ret = bus_register(&rpmsg_bus);
	if (ret) {
		pr_err("failed to register rpmsg bus: %d\n", ret);
		return ret;
	}

	ret = register_virtio_driver(&virtio_ipc_driver);
	if (ret) {
		pr_err("failed to register virtio driver: %d\n", ret);
		bus_unregister(&rpmsg_bus);
	}

	return ret;
}
module_init(rpmsg_init);

static void __exit rpmsg_fini(void)
{
	unregister_virtio_driver(&virtio_ipc_driver);
	bus_unregister(&rpmsg_bus);
}
module_exit(rpmsg_fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio-based remote processor messaging bus");
MODULE_LICENSE("GPL v2");