aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/pci/p2pdma.c
blob: 84ba3058eadaa919b5c0239544859dac3c242c45 (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
// SPDX-License-Identifier: GPL-2.0
/*
 * PCI Peer 2 Peer DMA support.
 *
 * Copyright (c) 2016-2018, Logan Gunthorpe
 * Copyright (c) 2016-2017, Microsemi Corporation
 * Copyright (c) 2017, Christoph Hellwig
 * Copyright (c) 2018, Eideticom Inc.
 */

#define pr_fmt(fmt) "pci-p2pdma: " fmt
#include <linux/ctype.h>
#include <linux/pci-p2pdma.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/genalloc.h>
#include <linux/memremap.h>
#include <linux/percpu-refcount.h>
#include <linux/random.h>
#include <linux/seq_buf.h>
#include <linux/iommu.h>

struct pci_p2pdma {
	struct percpu_ref devmap_ref;
	struct completion devmap_ref_done;
	struct gen_pool *pool;
	bool p2pmem_published;
};

static ssize_t size_show(struct device *dev, struct device_attribute *attr,
			 char *buf)
{
	struct pci_dev *pdev = to_pci_dev(dev);
	size_t size = 0;

	if (pdev->p2pdma->pool)
		size = gen_pool_size(pdev->p2pdma->pool);

	return snprintf(buf, PAGE_SIZE, "%zd\n", size);
}
static DEVICE_ATTR_RO(size);

static ssize_t available_show(struct device *dev, struct device_attribute *attr,
			      char *buf)
{
	struct pci_dev *pdev = to_pci_dev(dev);
	size_t avail = 0;

	if (pdev->p2pdma->pool)
		avail = gen_pool_avail(pdev->p2pdma->pool);

	return snprintf(buf, PAGE_SIZE, "%zd\n", avail);
}
static DEVICE_ATTR_RO(available);

static ssize_t published_show(struct device *dev, struct device_attribute *attr,
			      char *buf)
{
	struct pci_dev *pdev = to_pci_dev(dev);

	return snprintf(buf, PAGE_SIZE, "%d\n",
			pdev->p2pdma->p2pmem_published);
}
static DEVICE_ATTR_RO(published);

static struct attribute *p2pmem_attrs[] = {
	&dev_attr_size.attr,
	&dev_attr_available.attr,
	&dev_attr_published.attr,
	NULL,
};

static const struct attribute_group p2pmem_group = {
	.attrs = p2pmem_attrs,
	.name = "p2pmem",
};

static void pci_p2pdma_percpu_release(struct percpu_ref *ref)
{
	struct pci_p2pdma *p2p =
		container_of(ref, struct pci_p2pdma, devmap_ref);

	complete_all(&p2p->devmap_ref_done);
}

static void pci_p2pdma_percpu_kill(struct percpu_ref *ref)
{
	/*
	 * pci_p2pdma_add_resource() may be called multiple times
	 * by a driver and may register the percpu_kill devm action multiple
	 * times. We only want the first action to actually kill the
	 * percpu_ref.
	 */
	if (percpu_ref_is_dying(ref))
		return;

	percpu_ref_kill(ref);
}

static void pci_p2pdma_release(void *data)
{
	struct pci_dev *pdev = data;

	if (!pdev->p2pdma)
		return;

	wait_for_completion(&pdev->p2pdma->devmap_ref_done);
	percpu_ref_exit(&pdev->p2pdma->devmap_ref);

	gen_pool_destroy(pdev->p2pdma->pool);
	sysfs_remove_group(&pdev->dev.kobj, &p2pmem_group);
	pdev->p2pdma = NULL;
}

static int pci_p2pdma_setup(struct pci_dev *pdev)
{
	int error = -ENOMEM;
	struct pci_p2pdma *p2p;

	p2p = devm_kzalloc(&pdev->dev, sizeof(*p2p), GFP_KERNEL);
	if (!p2p)
		return -ENOMEM;

	p2p->pool = gen_pool_create(PAGE_SHIFT, dev_to_node(&pdev->dev));
	if (!p2p->pool)
		goto out;

	init_completion(&p2p->devmap_ref_done);
	error = percpu_ref_init(&p2p->devmap_ref,
			pci_p2pdma_percpu_release, 0, GFP_KERNEL);
	if (error)
		goto out_pool_destroy;

	error = devm_add_action_or_reset(&pdev->dev, pci_p2pdma_release, pdev);
	if (error)
		goto out_pool_destroy;

	pdev->p2pdma = p2p;

	error = sysfs_create_group(&pdev->dev.kobj, &p2pmem_group);
	if (error)
		goto out_pool_destroy;

	return 0;

out_pool_destroy:
	pdev->p2pdma = NULL;
	gen_pool_destroy(p2p->pool);
out:
	devm_kfree(&pdev->dev, p2p);
	return error;
}

/**
 * pci_p2pdma_add_resource - add memory for use as p2p memory
 * @pdev: the device to add the memory to
 * @bar: PCI BAR to add
 * @size: size of the memory to add, may be zero to use the whole BAR
 * @offset: offset into the PCI BAR
 *
 * The memory will be given ZONE_DEVICE struct pages so that it may
 * be used with any DMA request.
 */
int pci_p2pdma_add_resource(struct pci_dev *pdev, int bar, size_t size,
			    u64 offset)
{
	struct dev_pagemap *pgmap;
	void *addr;
	int error;

	if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
		return -EINVAL;

	if (offset >= pci_resource_len(pdev, bar))
		return -EINVAL;

	if (!size)
		size = pci_resource_len(pdev, bar) - offset;

	if (size + offset > pci_resource_len(pdev, bar))
		return -EINVAL;

	if (!pdev->p2pdma) {
		error = pci_p2pdma_setup(pdev);
		if (error)
			return error;
	}

	pgmap = devm_kzalloc(&pdev->dev, sizeof(*pgmap), GFP_KERNEL);
	if (!pgmap)
		return -ENOMEM;

	pgmap->res.start = pci_resource_start(pdev, bar) + offset;
	pgmap->res.end = pgmap->res.start + size - 1;
	pgmap->res.flags = pci_resource_flags(pdev, bar);
	pgmap->ref = &pdev->p2pdma->devmap_ref;
	pgmap->type = MEMORY_DEVICE_PCI_P2PDMA;
	pgmap->pci_p2pdma_bus_offset = pci_bus_address(pdev, bar) -
		pci_resource_start(pdev, bar);
	pgmap->kill = pci_p2pdma_percpu_kill;

	addr = devm_memremap_pages(&pdev->dev, pgmap);
	if (IS_ERR(addr)) {
		error = PTR_ERR(addr);
		goto pgmap_free;
	}

	error = gen_pool_add_virt(pdev->p2pdma->pool, (unsigned long)addr,
			pci_bus_address(pdev, bar) + offset,
			resource_size(&pgmap->res), dev_to_node(&pdev->dev));
	if (error)
		goto pgmap_free;

	pci_info(pdev, "added peer-to-peer DMA memory %pR\n",
		 &pgmap->res);

	return 0;

pgmap_free:
	devm_kfree(&pdev->dev, pgmap);
	return error;
}
EXPORT_SYMBOL_GPL(pci_p2pdma_add_resource);

/*
 * Note this function returns the parent PCI device with a
 * reference taken. It is the caller's responsibily to drop
 * the reference.
 */
static struct pci_dev *find_parent_pci_dev(struct device *dev)
{
	struct device *parent;

	dev = get_device(dev);

	while (dev) {
		if (dev_is_pci(dev))
			return to_pci_dev(dev);

		parent = get_device(dev->parent);
		put_device(dev);
		dev = parent;
	}

	return NULL;
}

/*
 * Check if a PCI bridge has its ACS redirection bits set to redirect P2P
 * TLPs upstream via ACS. Returns 1 if the packets will be redirected
 * upstream, 0 otherwise.
 */
static int pci_bridge_has_acs_redir(struct pci_dev *pdev)
{
	int pos;
	u16 ctrl;

	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ACS);
	if (!pos)
		return 0;

	pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);

	if (ctrl & (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC))
		return 1;

	return 0;
}

static void seq_buf_print_bus_devfn(struct seq_buf *buf, struct pci_dev *pdev)
{
	if (!buf)
		return;

	seq_buf_printf(buf, "%s;", pci_name(pdev));
}

/*
 * If we can't find a common upstream bridge take a look at the root
 * complex and compare it to a whitelist of known good hardware.
 */
static bool root_complex_whitelist(struct pci_dev *dev)
{
	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
	unsigned short vendor, device;

	if (iommu_present(dev->dev.bus))
		return false;

	if (!root)
		return false;

	vendor = root->vendor;
	device = root->device;
	pci_dev_put(root);

	/* AMD ZEN host bridges can do peer to peer */
	if (vendor == PCI_VENDOR_ID_AMD && device == 0x1450)
		return true;

	return false;
}

/*
 * Find the distance through the nearest common upstream bridge between
 * two PCI devices.
 *
 * If the two devices are the same device then 0 will be returned.
 *
 * If there are two virtual functions of the same device behind the same
 * bridge port then 2 will be returned (one step down to the PCIe switch,
 * then one step back to the same device).
 *
 * In the case where two devices are connected to the same PCIe switch, the
 * value 4 will be returned. This corresponds to the following PCI tree:
 *
 *     -+  Root Port
 *      \+ Switch Upstream Port
 *       +-+ Switch Downstream Port
 *       + \- Device A
 *       \-+ Switch Downstream Port
 *         \- Device B
 *
 * The distance is 4 because we traverse from Device A through the downstream
 * port of the switch, to the common upstream port, back up to the second
 * downstream port and then to Device B.
 *
 * Any two devices that don't have a common upstream bridge will return -1.
 * In this way devices on separate PCIe root ports will be rejected, which
 * is what we want for peer-to-peer seeing each PCIe root port defines a
 * separate hierarchy domain and there's no way to determine whether the root
 * complex supports forwarding between them.
 *
 * In the case where two devices are connected to different PCIe switches,
 * this function will still return a positive distance as long as both
 * switches eventually have a common upstream bridge. Note this covers
 * the case of using multiple PCIe switches to achieve a desired level of
 * fan-out from a root port. The exact distance will be a function of the
 * number of switches between Device A and Device B.
 *
 * If a bridge which has any ACS redirection bits set is in the path
 * then this functions will return -2. This is so we reject any
 * cases where the TLPs are forwarded up into the root complex.
 * In this case, a list of all infringing bridge addresses will be
 * populated in acs_list (assuming it's non-null) for printk purposes.
 */
static int upstream_bridge_distance(struct pci_dev *provider,
				    struct pci_dev *client,
				    struct seq_buf *acs_list)
{
	struct pci_dev *a = provider, *b = client, *bb;
	int dist_a = 0;
	int dist_b = 0;
	int acs_cnt = 0;

	/*
	 * Note, we don't need to take references to devices returned by
	 * pci_upstream_bridge() seeing we hold a reference to a child
	 * device which will already hold a reference to the upstream bridge.
	 */

	while (a) {
		dist_b = 0;

		if (pci_bridge_has_acs_redir(a)) {
			seq_buf_print_bus_devfn(acs_list, a);
			acs_cnt++;
		}

		bb = b;

		while (bb) {
			if (a == bb)
				goto check_b_path_acs;

			bb = pci_upstream_bridge(bb);
			dist_b++;
		}

		a = pci_upstream_bridge(a);
		dist_a++;
	}

	/*
	 * Allow the connection if both devices are on a whitelisted root
	 * complex, but add an arbitary large value to the distance.
	 */
	if (root_complex_whitelist(provider) &&
	    root_complex_whitelist(client))
		return 0x1000 + dist_a + dist_b;

	return -1;

check_b_path_acs:
	bb = b;

	while (bb) {
		if (a == bb)
			break;

		if (pci_bridge_has_acs_redir(bb)) {
			seq_buf_print_bus_devfn(acs_list, bb);
			acs_cnt++;
		}

		bb = pci_upstream_bridge(bb);
	}

	if (acs_cnt)
		return -2;

	return dist_a + dist_b;
}

static int upstream_bridge_distance_warn(struct pci_dev *provider,
					 struct pci_dev *client)
{
	struct seq_buf acs_list;
	int ret;

	seq_buf_init(&acs_list, kmalloc(PAGE_SIZE, GFP_KERNEL), PAGE_SIZE);
	if (!acs_list.buffer)
		return -ENOMEM;

	ret = upstream_bridge_distance(provider, client, &acs_list);
	if (ret == -2) {
		pci_warn(client, "cannot be used for peer-to-peer DMA as ACS redirect is set between the client and provider (%s)\n",
			 pci_name(provider));
		/* Drop final semicolon */
		acs_list.buffer[acs_list.len-1] = 0;
		pci_warn(client, "to disable ACS redirect for this path, add the kernel parameter: pci=disable_acs_redir=%s\n",
			 acs_list.buffer);

	} else if (ret < 0) {
		pci_warn(client, "cannot be used for peer-to-peer DMA as the client and provider (%s) do not share an upstream bridge\n",
			 pci_name(provider));
	}

	kfree(acs_list.buffer);

	return ret;
}

/**
 * pci_p2pdma_distance_many - Determive the cumulative distance between
 *	a p2pdma provider and the clients in use.
 * @provider: p2pdma provider to check against the client list
 * @clients: array of devices to check (NULL-terminated)
 * @num_clients: number of clients in the array
 * @verbose: if true, print warnings for devices when we return -1
 *
 * Returns -1 if any of the clients are not compatible (behind the same
 * root port as the provider), otherwise returns a positive number where
 * a lower number is the preferable choice. (If there's one client
 * that's the same as the provider it will return 0, which is best choice).
 *
 * For now, "compatible" means the provider and the clients are all behind
 * the same PCI root port. This cuts out cases that may work but is safest
 * for the user. Future work can expand this to white-list root complexes that
 * can safely forward between each ports.
 */
int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
			     int num_clients, bool verbose)
{
	bool not_supported = false;
	struct pci_dev *pci_client;
	int distance = 0;
	int i, ret;

	if (num_clients == 0)
		return -1;

	for (i = 0; i < num_clients; i++) {
		pci_client = find_parent_pci_dev(clients[i]);
		if (!pci_client) {
			if (verbose)
				dev_warn(clients[i],
					 "cannot be used for peer-to-peer DMA as it is not a PCI device\n");
			return -1;
		}

		if (verbose)
			ret = upstream_bridge_distance_warn(provider,
							    pci_client);
		else
			ret = upstream_bridge_distance(provider, pci_client,
						       NULL);

		pci_dev_put(pci_client);

		if (ret < 0)
			not_supported = true;

		if (not_supported && !verbose)
			break;

		distance += ret;
	}

	if (not_supported)
		return -1;

	return distance;
}
EXPORT_SYMBOL_GPL(pci_p2pdma_distance_many);

/**
 * pci_has_p2pmem - check if a given PCI device has published any p2pmem
 * @pdev: PCI device to check
 */
bool pci_has_p2pmem(struct pci_dev *pdev)
{
	return pdev->p2pdma && pdev->p2pdma->p2pmem_published;
}
EXPORT_SYMBOL_GPL(pci_has_p2pmem);

/**
 * pci_p2pmem_find - find a peer-to-peer DMA memory device compatible with
 *	the specified list of clients and shortest distance (as determined
 *	by pci_p2pmem_dma())
 * @clients: array of devices to check (NULL-terminated)
 * @num_clients: number of client devices in the list
 *
 * If multiple devices are behind the same switch, the one "closest" to the
 * client devices in use will be chosen first. (So if one of the providers is
 * the same as one of the clients, that provider will be used ahead of any
 * other providers that are unrelated). If multiple providers are an equal
 * distance away, one will be chosen at random.
 *
 * Returns a pointer to the PCI device with a reference taken (use pci_dev_put
 * to return the reference) or NULL if no compatible device is found. The
 * found provider will also be assigned to the client list.
 */
struct pci_dev *pci_p2pmem_find_many(struct device **clients, int num_clients)
{
	struct pci_dev *pdev = NULL;
	int distance;
	int closest_distance = INT_MAX;
	struct pci_dev **closest_pdevs;
	int dev_cnt = 0;
	const int max_devs = PAGE_SIZE / sizeof(*closest_pdevs);
	int i;

	closest_pdevs = kmalloc(PAGE_SIZE, GFP_KERNEL);
	if (!closest_pdevs)
		return NULL;

	while ((pdev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, pdev))) {
		if (!pci_has_p2pmem(pdev))
			continue;

		distance = pci_p2pdma_distance_many(pdev, clients,
						    num_clients, false);
		if (distance < 0 || distance > closest_distance)
			continue;

		if (distance == closest_distance && dev_cnt >= max_devs)
			continue;

		if (distance < closest_distance) {
			for (i = 0; i < dev_cnt; i++)
				pci_dev_put(closest_pdevs[i]);

			dev_cnt = 0;
			closest_distance = distance;
		}

		closest_pdevs[dev_cnt++] = pci_dev_get(pdev);
	}

	if (dev_cnt)
		pdev = pci_dev_get(closest_pdevs[prandom_u32_max(dev_cnt)]);

	for (i = 0; i < dev_cnt; i++)
		pci_dev_put(closest_pdevs[i]);

	kfree(closest_pdevs);
	return pdev;
}
EXPORT_SYMBOL_GPL(pci_p2pmem_find_many);

/**
 * pci_alloc_p2p_mem - allocate peer-to-peer DMA memory
 * @pdev: the device to allocate memory from
 * @size: number of bytes to allocate
 *
 * Returns the allocated memory or NULL on error.
 */
void *pci_alloc_p2pmem(struct pci_dev *pdev, size_t size)
{
	void *ret;

	if (unlikely(!pdev->p2pdma))
		return NULL;

	if (unlikely(!percpu_ref_tryget_live(&pdev->p2pdma->devmap_ref)))
		return NULL;

	ret = (void *)gen_pool_alloc(pdev->p2pdma->pool, size);

	if (unlikely(!ret))
		percpu_ref_put(&pdev->p2pdma->devmap_ref);

	return ret;
}
EXPORT_SYMBOL_GPL(pci_alloc_p2pmem);

/**
 * pci_free_p2pmem - free peer-to-peer DMA memory
 * @pdev: the device the memory was allocated from
 * @addr: address of the memory that was allocated
 * @size: number of bytes that were allocated
 */
void pci_free_p2pmem(struct pci_dev *pdev, void *addr, size_t size)
{
	gen_pool_free(pdev->p2pdma->pool, (uintptr_t)addr, size);
	percpu_ref_put(&pdev->p2pdma->devmap_ref);
}
EXPORT_SYMBOL_GPL(pci_free_p2pmem);

/**
 * pci_virt_to_bus - return the PCI bus address for a given virtual
 *	address obtained with pci_alloc_p2pmem()
 * @pdev: the device the memory was allocated from
 * @addr: address of the memory that was allocated
 */
pci_bus_addr_t pci_p2pmem_virt_to_bus(struct pci_dev *pdev, void *addr)
{
	if (!addr)
		return 0;
	if (!pdev->p2pdma)
		return 0;

	/*
	 * Note: when we added the memory to the pool we used the PCI
	 * bus address as the physical address. So gen_pool_virt_to_phys()
	 * actually returns the bus address despite the misleading name.
	 */
	return gen_pool_virt_to_phys(pdev->p2pdma->pool, (unsigned long)addr);
}
EXPORT_SYMBOL_GPL(pci_p2pmem_virt_to_bus);

/**
 * pci_p2pmem_alloc_sgl - allocate peer-to-peer DMA memory in a scatterlist
 * @pdev: the device to allocate memory from
 * @nents: the number of SG entries in the list
 * @length: number of bytes to allocate
 *
 * Return: %NULL on error or &struct scatterlist pointer and @nents on success
 */
struct scatterlist *pci_p2pmem_alloc_sgl(struct pci_dev *pdev,
					 unsigned int *nents, u32 length)
{
	struct scatterlist *sg;
	void *addr;

	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
	if (!sg)
		return NULL;

	sg_init_table(sg, 1);

	addr = pci_alloc_p2pmem(pdev, length);
	if (!addr)
		goto out_free_sg;

	sg_set_buf(sg, addr, length);
	*nents = 1;
	return sg;

out_free_sg:
	kfree(sg);
	return NULL;
}
EXPORT_SYMBOL_GPL(pci_p2pmem_alloc_sgl);

/**
 * pci_p2pmem_free_sgl - free a scatterlist allocated by pci_p2pmem_alloc_sgl()
 * @pdev: the device to allocate memory from
 * @sgl: the allocated scatterlist
 */
void pci_p2pmem_free_sgl(struct pci_dev *pdev, struct scatterlist *sgl)
{
	struct scatterlist *sg;
	int count;

	for_each_sg(sgl, sg, INT_MAX, count) {
		if (!sg)
			break;

		pci_free_p2pmem(pdev, sg_virt(sg), sg->length);
	}
	kfree(sgl);
}
EXPORT_SYMBOL_GPL(pci_p2pmem_free_sgl);

/**
 * pci_p2pmem_publish - publish the peer-to-peer DMA memory for use by
 *	other devices with pci_p2pmem_find()
 * @pdev: the device with peer-to-peer DMA memory to publish
 * @publish: set to true to publish the memory, false to unpublish it
 *
 * Published memory can be used by other PCI device drivers for
 * peer-2-peer DMA operations. Non-published memory is reserved for
 * exclusive use of the device driver that registers the peer-to-peer
 * memory.
 */
void pci_p2pmem_publish(struct pci_dev *pdev, bool publish)
{
	if (pdev->p2pdma)
		pdev->p2pdma->p2pmem_published = publish;
}
EXPORT_SYMBOL_GPL(pci_p2pmem_publish);

/**
 * pci_p2pdma_map_sg - map a PCI peer-to-peer scatterlist for DMA
 * @dev: device doing the DMA request
 * @sg: scatter list to map
 * @nents: elements in the scatterlist
 * @dir: DMA direction
 *
 * Scatterlists mapped with this function should not be unmapped in any way.
 *
 * Returns the number of SG entries mapped or 0 on error.
 */
int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
		      enum dma_data_direction dir)
{
	struct dev_pagemap *pgmap;
	struct scatterlist *s;
	phys_addr_t paddr;
	int i;

	/*
	 * p2pdma mappings are not compatible with devices that use
	 * dma_virt_ops. If the upper layers do the right thing
	 * this should never happen because it will be prevented
	 * by the check in pci_p2pdma_add_client()
	 */
	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
			 dev->dma_ops == &dma_virt_ops))
		return 0;

	for_each_sg(sg, s, nents, i) {
		pgmap = sg_page(s)->pgmap;
		paddr = sg_phys(s);

		s->dma_address = paddr - pgmap->pci_p2pdma_bus_offset;
		sg_dma_len(s) = s->length;
	}

	return nents;
}
EXPORT_SYMBOL_GPL(pci_p2pdma_map_sg);

/**
 * pci_p2pdma_enable_store - parse a configfs/sysfs attribute store
 *		to enable p2pdma
 * @page: contents of the value to be stored
 * @p2p_dev: returns the PCI device that was selected to be used
 *		(if one was specified in the stored value)
 * @use_p2pdma: returns whether to enable p2pdma or not
 *
 * Parses an attribute value to decide whether to enable p2pdma.
 * The value can select a PCI device (using its full BDF device
 * name) or a boolean (in any format strtobool() accepts). A false
 * value disables p2pdma, a true value expects the caller
 * to automatically find a compatible device and specifying a PCI device
 * expects the caller to use the specific provider.
 *
 * pci_p2pdma_enable_show() should be used as the show operation for
 * the attribute.
 *
 * Returns 0 on success
 */
int pci_p2pdma_enable_store(const char *page, struct pci_dev **p2p_dev,
			    bool *use_p2pdma)
{
	struct device *dev;

	dev = bus_find_device_by_name(&pci_bus_type, NULL, page);
	if (dev) {
		*use_p2pdma = true;
		*p2p_dev = to_pci_dev(dev);

		if (!pci_has_p2pmem(*p2p_dev)) {
			pci_err(*p2p_dev,
				"PCI device has no peer-to-peer memory: %s\n",
				page);
			pci_dev_put(*p2p_dev);
			return -ENODEV;
		}

		return 0;
	} else if ((page[0] == '0' || page[0] == '1') && !iscntrl(page[1])) {
		/*
		 * If the user enters a PCI device that  doesn't exist
		 * like "0000:01:00.1", we don't want strtobool to think
		 * it's a '0' when it's clearly not what the user wanted.
		 * So we require 0's and 1's to be exactly one character.
		 */
	} else if (!strtobool(page, use_p2pdma)) {
		return 0;
	}

	pr_err("No such PCI device: %.*s\n", (int)strcspn(page, "\n"), page);
	return -ENODEV;
}
EXPORT_SYMBOL_GPL(pci_p2pdma_enable_store);

/**
 * pci_p2pdma_enable_show - show a configfs/sysfs attribute indicating
 *		whether p2pdma is enabled
 * @page: contents of the stored value
 * @p2p_dev: the selected p2p device (NULL if no device is selected)
 * @use_p2pdma: whether p2pdma has been enabled
 *
 * Attributes that use pci_p2pdma_enable_store() should use this function
 * to show the value of the attribute.
 *
 * Returns 0 on success
 */
ssize_t pci_p2pdma_enable_show(char *page, struct pci_dev *p2p_dev,
			       bool use_p2pdma)
{
	if (!use_p2pdma)
		return sprintf(page, "0\n");

	if (!p2p_dev)
		return sprintf(page, "1\n");

	return sprintf(page, "%s\n", pci_name(p2p_dev));
}
EXPORT_SYMBOL_GPL(pci_p2pdma_enable_show);