xref: /openbmc/linux/drivers/hwtracing/stm/core.c (revision 8ee90c5c)
1 /*
2  * System Trace Module (STM) infrastructure
3  * Copyright (c) 2014, Intel Corporation.
4  *
5  * This program is free software; you can redistribute it and/or modify it
6  * under the terms and conditions of the GNU General Public License,
7  * version 2, as published by the Free Software Foundation.
8  *
9  * This program is distributed in the hope it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
12  * more details.
13  *
14  * STM class implements generic infrastructure for  System Trace Module devices
15  * as defined in MIPI STPv2 specification.
16  */
17 
18 #include <linux/pm_runtime.h>
19 #include <linux/uaccess.h>
20 #include <linux/kernel.h>
21 #include <linux/module.h>
22 #include <linux/device.h>
23 #include <linux/compat.h>
24 #include <linux/kdev_t.h>
25 #include <linux/srcu.h>
26 #include <linux/slab.h>
27 #include <linux/stm.h>
28 #include <linux/fs.h>
29 #include <linux/mm.h>
30 #include "stm.h"
31 
32 #include <uapi/linux/stm.h>
33 
34 static unsigned int stm_core_up;
35 
36 /*
37  * The SRCU here makes sure that STM device doesn't disappear from under a
38  * stm_source_write() caller, which may want to have as little overhead as
39  * possible.
40  */
41 static struct srcu_struct stm_source_srcu;
42 
43 static ssize_t masters_show(struct device *dev,
44 			    struct device_attribute *attr,
45 			    char *buf)
46 {
47 	struct stm_device *stm = to_stm_device(dev);
48 	int ret;
49 
50 	ret = sprintf(buf, "%u %u\n", stm->data->sw_start, stm->data->sw_end);
51 
52 	return ret;
53 }
54 
55 static DEVICE_ATTR_RO(masters);
56 
57 static ssize_t channels_show(struct device *dev,
58 			     struct device_attribute *attr,
59 			     char *buf)
60 {
61 	struct stm_device *stm = to_stm_device(dev);
62 	int ret;
63 
64 	ret = sprintf(buf, "%u\n", stm->data->sw_nchannels);
65 
66 	return ret;
67 }
68 
69 static DEVICE_ATTR_RO(channels);
70 
71 static ssize_t hw_override_show(struct device *dev,
72 				struct device_attribute *attr,
73 				char *buf)
74 {
75 	struct stm_device *stm = to_stm_device(dev);
76 	int ret;
77 
78 	ret = sprintf(buf, "%u\n", stm->data->hw_override);
79 
80 	return ret;
81 }
82 
83 static DEVICE_ATTR_RO(hw_override);
84 
85 static struct attribute *stm_attrs[] = {
86 	&dev_attr_masters.attr,
87 	&dev_attr_channels.attr,
88 	&dev_attr_hw_override.attr,
89 	NULL,
90 };
91 
92 ATTRIBUTE_GROUPS(stm);
93 
94 static struct class stm_class = {
95 	.name		= "stm",
96 	.dev_groups	= stm_groups,
97 };
98 
99 static int stm_dev_match(struct device *dev, const void *data)
100 {
101 	const char *name = data;
102 
103 	return sysfs_streq(name, dev_name(dev));
104 }
105 
106 /**
107  * stm_find_device() - find stm device by name
108  * @buf:	character buffer containing the name
109  *
110  * This is called when either policy gets assigned to an stm device or an
111  * stm_source device gets linked to an stm device.
112  *
113  * This grabs device's reference (get_device()) and module reference, both
114  * of which the calling path needs to make sure to drop with stm_put_device().
115  *
116  * Return:	stm device pointer or null if lookup failed.
117  */
118 struct stm_device *stm_find_device(const char *buf)
119 {
120 	struct stm_device *stm;
121 	struct device *dev;
122 
123 	if (!stm_core_up)
124 		return NULL;
125 
126 	dev = class_find_device(&stm_class, NULL, buf, stm_dev_match);
127 	if (!dev)
128 		return NULL;
129 
130 	stm = to_stm_device(dev);
131 	if (!try_module_get(stm->owner)) {
132 		/* matches class_find_device() above */
133 		put_device(dev);
134 		return NULL;
135 	}
136 
137 	return stm;
138 }
139 
140 /**
141  * stm_put_device() - drop references on the stm device
142  * @stm:	stm device, previously acquired by stm_find_device()
143  *
144  * This drops the module reference and device reference taken by
145  * stm_find_device() or stm_char_open().
146  */
147 void stm_put_device(struct stm_device *stm)
148 {
149 	module_put(stm->owner);
150 	put_device(&stm->dev);
151 }
152 
153 /*
154  * Internally we only care about software-writable masters here, that is the
155  * ones in the range [stm_data->sw_start..stm_data..sw_end], however we need
156  * original master numbers to be visible externally, since they are the ones
157  * that will appear in the STP stream. Thus, the internal bookkeeping uses
158  * $master - stm_data->sw_start to reference master descriptors and such.
159  */
160 
161 #define __stm_master(_s, _m)				\
162 	((_s)->masters[(_m) - (_s)->data->sw_start])
163 
164 static inline struct stp_master *
165 stm_master(struct stm_device *stm, unsigned int idx)
166 {
167 	if (idx < stm->data->sw_start || idx > stm->data->sw_end)
168 		return NULL;
169 
170 	return __stm_master(stm, idx);
171 }
172 
173 static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
174 {
175 	struct stp_master *master;
176 	size_t size;
177 
178 	size = ALIGN(stm->data->sw_nchannels, 8) / 8;
179 	size += sizeof(struct stp_master);
180 	master = kzalloc(size, GFP_ATOMIC);
181 	if (!master)
182 		return -ENOMEM;
183 
184 	master->nr_free = stm->data->sw_nchannels;
185 	__stm_master(stm, idx) = master;
186 
187 	return 0;
188 }
189 
190 static void stp_master_free(struct stm_device *stm, unsigned int idx)
191 {
192 	struct stp_master *master = stm_master(stm, idx);
193 
194 	if (!master)
195 		return;
196 
197 	__stm_master(stm, idx) = NULL;
198 	kfree(master);
199 }
200 
201 static void stm_output_claim(struct stm_device *stm, struct stm_output *output)
202 {
203 	struct stp_master *master = stm_master(stm, output->master);
204 
205 	lockdep_assert_held(&stm->mc_lock);
206 	lockdep_assert_held(&output->lock);
207 
208 	if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
209 		return;
210 
211 	bitmap_allocate_region(&master->chan_map[0], output->channel,
212 			       ilog2(output->nr_chans));
213 
214 	master->nr_free -= output->nr_chans;
215 }
216 
217 static void
218 stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
219 {
220 	struct stp_master *master = stm_master(stm, output->master);
221 
222 	lockdep_assert_held(&stm->mc_lock);
223 	lockdep_assert_held(&output->lock);
224 
225 	bitmap_release_region(&master->chan_map[0], output->channel,
226 			      ilog2(output->nr_chans));
227 
228 	output->nr_chans = 0;
229 	master->nr_free += output->nr_chans;
230 }
231 
232 /*
233  * This is like bitmap_find_free_region(), except it can ignore @start bits
234  * at the beginning.
235  */
236 static int find_free_channels(unsigned long *bitmap, unsigned int start,
237 			      unsigned int end, unsigned int width)
238 {
239 	unsigned int pos;
240 	int i;
241 
242 	for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
243 		pos = find_next_zero_bit(bitmap, end + 1, pos);
244 		if (pos + width > end + 1)
245 			break;
246 
247 		if (pos & (width - 1))
248 			continue;
249 
250 		for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
251 			;
252 		if (i == width)
253 			return pos;
254 	}
255 
256 	return -1;
257 }
258 
259 static int
260 stm_find_master_chan(struct stm_device *stm, unsigned int width,
261 		     unsigned int *mstart, unsigned int mend,
262 		     unsigned int *cstart, unsigned int cend)
263 {
264 	struct stp_master *master;
265 	unsigned int midx;
266 	int pos, err;
267 
268 	for (midx = *mstart; midx <= mend; midx++) {
269 		if (!stm_master(stm, midx)) {
270 			err = stp_master_alloc(stm, midx);
271 			if (err)
272 				return err;
273 		}
274 
275 		master = stm_master(stm, midx);
276 
277 		if (!master->nr_free)
278 			continue;
279 
280 		pos = find_free_channels(master->chan_map, *cstart, cend,
281 					 width);
282 		if (pos < 0)
283 			continue;
284 
285 		*mstart = midx;
286 		*cstart = pos;
287 		return 0;
288 	}
289 
290 	return -ENOSPC;
291 }
292 
293 static int stm_output_assign(struct stm_device *stm, unsigned int width,
294 			     struct stp_policy_node *policy_node,
295 			     struct stm_output *output)
296 {
297 	unsigned int midx, cidx, mend, cend;
298 	int ret = -EINVAL;
299 
300 	if (width > stm->data->sw_nchannels)
301 		return -EINVAL;
302 
303 	if (policy_node) {
304 		stp_policy_node_get_ranges(policy_node,
305 					   &midx, &mend, &cidx, &cend);
306 	} else {
307 		midx = stm->data->sw_start;
308 		cidx = 0;
309 		mend = stm->data->sw_end;
310 		cend = stm->data->sw_nchannels - 1;
311 	}
312 
313 	spin_lock(&stm->mc_lock);
314 	spin_lock(&output->lock);
315 	/* output is already assigned -- shouldn't happen */
316 	if (WARN_ON_ONCE(output->nr_chans))
317 		goto unlock;
318 
319 	ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
320 	if (ret < 0)
321 		goto unlock;
322 
323 	output->master = midx;
324 	output->channel = cidx;
325 	output->nr_chans = width;
326 	stm_output_claim(stm, output);
327 	dev_dbg(&stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
328 
329 	ret = 0;
330 unlock:
331 	spin_unlock(&output->lock);
332 	spin_unlock(&stm->mc_lock);
333 
334 	return ret;
335 }
336 
337 static void stm_output_free(struct stm_device *stm, struct stm_output *output)
338 {
339 	spin_lock(&stm->mc_lock);
340 	spin_lock(&output->lock);
341 	if (output->nr_chans)
342 		stm_output_disclaim(stm, output);
343 	spin_unlock(&output->lock);
344 	spin_unlock(&stm->mc_lock);
345 }
346 
347 static void stm_output_init(struct stm_output *output)
348 {
349 	spin_lock_init(&output->lock);
350 }
351 
352 static int major_match(struct device *dev, const void *data)
353 {
354 	unsigned int major = *(unsigned int *)data;
355 
356 	return MAJOR(dev->devt) == major;
357 }
358 
359 static int stm_char_open(struct inode *inode, struct file *file)
360 {
361 	struct stm_file *stmf;
362 	struct device *dev;
363 	unsigned int major = imajor(inode);
364 	int err = -ENOMEM;
365 
366 	dev = class_find_device(&stm_class, NULL, &major, major_match);
367 	if (!dev)
368 		return -ENODEV;
369 
370 	stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
371 	if (!stmf)
372 		goto err_put_device;
373 
374 	err = -ENODEV;
375 	stm_output_init(&stmf->output);
376 	stmf->stm = to_stm_device(dev);
377 
378 	if (!try_module_get(stmf->stm->owner))
379 		goto err_free;
380 
381 	file->private_data = stmf;
382 
383 	return nonseekable_open(inode, file);
384 
385 err_free:
386 	kfree(stmf);
387 err_put_device:
388 	/* matches class_find_device() above */
389 	put_device(dev);
390 
391 	return err;
392 }
393 
394 static int stm_char_release(struct inode *inode, struct file *file)
395 {
396 	struct stm_file *stmf = file->private_data;
397 	struct stm_device *stm = stmf->stm;
398 
399 	if (stm->data->unlink)
400 		stm->data->unlink(stm->data, stmf->output.master,
401 				  stmf->output.channel);
402 
403 	stm_output_free(stm, &stmf->output);
404 
405 	/*
406 	 * matches the stm_char_open()'s
407 	 * class_find_device() + try_module_get()
408 	 */
409 	stm_put_device(stm);
410 	kfree(stmf);
411 
412 	return 0;
413 }
414 
415 static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
416 {
417 	struct stm_device *stm = stmf->stm;
418 	int ret;
419 
420 	stmf->policy_node = stp_policy_node_lookup(stm, id);
421 
422 	ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
423 
424 	if (stmf->policy_node)
425 		stp_policy_node_put(stmf->policy_node);
426 
427 	return ret;
428 }
429 
430 static ssize_t notrace stm_write(struct stm_data *data, unsigned int master,
431 			  unsigned int channel, const char *buf, size_t count)
432 {
433 	unsigned int flags = STP_PACKET_TIMESTAMPED;
434 	const unsigned char *p = buf, nil = 0;
435 	size_t pos;
436 	ssize_t sz;
437 
438 	for (pos = 0, p = buf; count > pos; pos += sz, p += sz) {
439 		sz = min_t(unsigned int, count - pos, 8);
440 		sz = data->packet(data, master, channel, STP_PACKET_DATA, flags,
441 				  sz, p);
442 		flags = 0;
443 
444 		if (sz < 0)
445 			break;
446 	}
447 
448 	data->packet(data, master, channel, STP_PACKET_FLAG, 0, 0, &nil);
449 
450 	return pos;
451 }
452 
453 static ssize_t stm_char_write(struct file *file, const char __user *buf,
454 			      size_t count, loff_t *ppos)
455 {
456 	struct stm_file *stmf = file->private_data;
457 	struct stm_device *stm = stmf->stm;
458 	char *kbuf;
459 	int err;
460 
461 	if (count + 1 > PAGE_SIZE)
462 		count = PAGE_SIZE - 1;
463 
464 	/*
465 	 * if no m/c have been assigned to this writer up to this
466 	 * point, use "default" policy entry
467 	 */
468 	if (!stmf->output.nr_chans) {
469 		err = stm_file_assign(stmf, "default", 1);
470 		/*
471 		 * EBUSY means that somebody else just assigned this
472 		 * output, which is just fine for write()
473 		 */
474 		if (err && err != -EBUSY)
475 			return err;
476 	}
477 
478 	kbuf = kmalloc(count + 1, GFP_KERNEL);
479 	if (!kbuf)
480 		return -ENOMEM;
481 
482 	err = copy_from_user(kbuf, buf, count);
483 	if (err) {
484 		kfree(kbuf);
485 		return -EFAULT;
486 	}
487 
488 	pm_runtime_get_sync(&stm->dev);
489 
490 	count = stm_write(stm->data, stmf->output.master, stmf->output.channel,
491 			  kbuf, count);
492 
493 	pm_runtime_mark_last_busy(&stm->dev);
494 	pm_runtime_put_autosuspend(&stm->dev);
495 	kfree(kbuf);
496 
497 	return count;
498 }
499 
500 static void stm_mmap_open(struct vm_area_struct *vma)
501 {
502 	struct stm_file *stmf = vma->vm_file->private_data;
503 	struct stm_device *stm = stmf->stm;
504 
505 	pm_runtime_get(&stm->dev);
506 }
507 
508 static void stm_mmap_close(struct vm_area_struct *vma)
509 {
510 	struct stm_file *stmf = vma->vm_file->private_data;
511 	struct stm_device *stm = stmf->stm;
512 
513 	pm_runtime_mark_last_busy(&stm->dev);
514 	pm_runtime_put_autosuspend(&stm->dev);
515 }
516 
517 static const struct vm_operations_struct stm_mmap_vmops = {
518 	.open	= stm_mmap_open,
519 	.close	= stm_mmap_close,
520 };
521 
522 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
523 {
524 	struct stm_file *stmf = file->private_data;
525 	struct stm_device *stm = stmf->stm;
526 	unsigned long size, phys;
527 
528 	if (!stm->data->mmio_addr)
529 		return -EOPNOTSUPP;
530 
531 	if (vma->vm_pgoff)
532 		return -EINVAL;
533 
534 	size = vma->vm_end - vma->vm_start;
535 
536 	if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
537 		return -EINVAL;
538 
539 	phys = stm->data->mmio_addr(stm->data, stmf->output.master,
540 				    stmf->output.channel,
541 				    stmf->output.nr_chans);
542 
543 	if (!phys)
544 		return -EINVAL;
545 
546 	pm_runtime_get_sync(&stm->dev);
547 
548 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
549 	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
550 	vma->vm_ops = &stm_mmap_vmops;
551 	vm_iomap_memory(vma, phys, size);
552 
553 	return 0;
554 }
555 
556 static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
557 {
558 	struct stm_device *stm = stmf->stm;
559 	struct stp_policy_id *id;
560 	int ret = -EINVAL;
561 	u32 size;
562 
563 	if (stmf->output.nr_chans)
564 		return -EBUSY;
565 
566 	if (copy_from_user(&size, arg, sizeof(size)))
567 		return -EFAULT;
568 
569 	if (size < sizeof(*id) || size >= PATH_MAX + sizeof(*id))
570 		return -EINVAL;
571 
572 	/*
573 	 * size + 1 to make sure the .id string at the bottom is terminated,
574 	 * which is also why memdup_user() is not useful here
575 	 */
576 	id = kzalloc(size + 1, GFP_KERNEL);
577 	if (!id)
578 		return -ENOMEM;
579 
580 	if (copy_from_user(id, arg, size)) {
581 		ret = -EFAULT;
582 		goto err_free;
583 	}
584 
585 	if (id->__reserved_0 || id->__reserved_1)
586 		goto err_free;
587 
588 	if (id->width < 1 ||
589 	    id->width > PAGE_SIZE / stm->data->sw_mmiosz)
590 		goto err_free;
591 
592 	ret = stm_file_assign(stmf, id->id, id->width);
593 	if (ret)
594 		goto err_free;
595 
596 	if (stm->data->link)
597 		ret = stm->data->link(stm->data, stmf->output.master,
598 				      stmf->output.channel);
599 
600 	if (ret)
601 		stm_output_free(stmf->stm, &stmf->output);
602 
603 err_free:
604 	kfree(id);
605 
606 	return ret;
607 }
608 
609 static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
610 {
611 	struct stp_policy_id id = {
612 		.size		= sizeof(id),
613 		.master		= stmf->output.master,
614 		.channel	= stmf->output.channel,
615 		.width		= stmf->output.nr_chans,
616 		.__reserved_0	= 0,
617 		.__reserved_1	= 0,
618 	};
619 
620 	return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
621 }
622 
623 static long
624 stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
625 {
626 	struct stm_file *stmf = file->private_data;
627 	struct stm_data *stm_data = stmf->stm->data;
628 	int err = -ENOTTY;
629 	u64 options;
630 
631 	switch (cmd) {
632 	case STP_POLICY_ID_SET:
633 		err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
634 		if (err)
635 			return err;
636 
637 		return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
638 
639 	case STP_POLICY_ID_GET:
640 		return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
641 
642 	case STP_SET_OPTIONS:
643 		if (copy_from_user(&options, (u64 __user *)arg, sizeof(u64)))
644 			return -EFAULT;
645 
646 		if (stm_data->set_options)
647 			err = stm_data->set_options(stm_data,
648 						    stmf->output.master,
649 						    stmf->output.channel,
650 						    stmf->output.nr_chans,
651 						    options);
652 
653 		break;
654 	default:
655 		break;
656 	}
657 
658 	return err;
659 }
660 
661 #ifdef CONFIG_COMPAT
662 static long
663 stm_char_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
664 {
665 	return stm_char_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
666 }
667 #else
668 #define stm_char_compat_ioctl	NULL
669 #endif
670 
671 static const struct file_operations stm_fops = {
672 	.open		= stm_char_open,
673 	.release	= stm_char_release,
674 	.write		= stm_char_write,
675 	.mmap		= stm_char_mmap,
676 	.unlocked_ioctl	= stm_char_ioctl,
677 	.compat_ioctl	= stm_char_compat_ioctl,
678 	.llseek		= no_llseek,
679 };
680 
681 static void stm_device_release(struct device *dev)
682 {
683 	struct stm_device *stm = to_stm_device(dev);
684 
685 	kfree(stm);
686 }
687 
688 int stm_register_device(struct device *parent, struct stm_data *stm_data,
689 			struct module *owner)
690 {
691 	struct stm_device *stm;
692 	unsigned int nmasters;
693 	int err = -ENOMEM;
694 
695 	if (!stm_core_up)
696 		return -EPROBE_DEFER;
697 
698 	if (!stm_data->packet || !stm_data->sw_nchannels)
699 		return -EINVAL;
700 
701 	nmasters = stm_data->sw_end - stm_data->sw_start + 1;
702 	stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
703 	if (!stm)
704 		return -ENOMEM;
705 
706 	stm->major = register_chrdev(0, stm_data->name, &stm_fops);
707 	if (stm->major < 0)
708 		goto err_free;
709 
710 	device_initialize(&stm->dev);
711 	stm->dev.devt = MKDEV(stm->major, 0);
712 	stm->dev.class = &stm_class;
713 	stm->dev.parent = parent;
714 	stm->dev.release = stm_device_release;
715 
716 	mutex_init(&stm->link_mutex);
717 	spin_lock_init(&stm->link_lock);
718 	INIT_LIST_HEAD(&stm->link_list);
719 
720 	/* initialize the object before it is accessible via sysfs */
721 	spin_lock_init(&stm->mc_lock);
722 	mutex_init(&stm->policy_mutex);
723 	stm->sw_nmasters = nmasters;
724 	stm->owner = owner;
725 	stm->data = stm_data;
726 	stm_data->stm = stm;
727 
728 	err = kobject_set_name(&stm->dev.kobj, "%s", stm_data->name);
729 	if (err)
730 		goto err_device;
731 
732 	err = device_add(&stm->dev);
733 	if (err)
734 		goto err_device;
735 
736 	/*
737 	 * Use delayed autosuspend to avoid bouncing back and forth
738 	 * on recurring character device writes, with the initial
739 	 * delay time of 2 seconds.
740 	 */
741 	pm_runtime_no_callbacks(&stm->dev);
742 	pm_runtime_use_autosuspend(&stm->dev);
743 	pm_runtime_set_autosuspend_delay(&stm->dev, 2000);
744 	pm_runtime_set_suspended(&stm->dev);
745 	pm_runtime_enable(&stm->dev);
746 
747 	return 0;
748 
749 err_device:
750 	unregister_chrdev(stm->major, stm_data->name);
751 
752 	/* matches device_initialize() above */
753 	put_device(&stm->dev);
754 err_free:
755 	kfree(stm);
756 
757 	return err;
758 }
759 EXPORT_SYMBOL_GPL(stm_register_device);
760 
761 static int __stm_source_link_drop(struct stm_source_device *src,
762 				  struct stm_device *stm);
763 
764 void stm_unregister_device(struct stm_data *stm_data)
765 {
766 	struct stm_device *stm = stm_data->stm;
767 	struct stm_source_device *src, *iter;
768 	int i, ret;
769 
770 	pm_runtime_dont_use_autosuspend(&stm->dev);
771 	pm_runtime_disable(&stm->dev);
772 
773 	mutex_lock(&stm->link_mutex);
774 	list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
775 		ret = __stm_source_link_drop(src, stm);
776 		/*
777 		 * src <-> stm link must not change under the same
778 		 * stm::link_mutex, so complain loudly if it has;
779 		 * also in this situation ret!=0 means this src is
780 		 * not connected to this stm and it should be otherwise
781 		 * safe to proceed with the tear-down of stm.
782 		 */
783 		WARN_ON_ONCE(ret);
784 	}
785 	mutex_unlock(&stm->link_mutex);
786 
787 	synchronize_srcu(&stm_source_srcu);
788 
789 	unregister_chrdev(stm->major, stm_data->name);
790 
791 	mutex_lock(&stm->policy_mutex);
792 	if (stm->policy)
793 		stp_policy_unbind(stm->policy);
794 	mutex_unlock(&stm->policy_mutex);
795 
796 	for (i = stm->data->sw_start; i <= stm->data->sw_end; i++)
797 		stp_master_free(stm, i);
798 
799 	device_unregister(&stm->dev);
800 	stm_data->stm = NULL;
801 }
802 EXPORT_SYMBOL_GPL(stm_unregister_device);
803 
804 /*
805  * stm::link_list access serialization uses a spinlock and a mutex; holding
806  * either of them guarantees that the list is stable; modification requires
807  * holding both of them.
808  *
809  * Lock ordering is as follows:
810  *   stm::link_mutex
811  *     stm::link_lock
812  *       src::link_lock
813  */
814 
815 /**
816  * stm_source_link_add() - connect an stm_source device to an stm device
817  * @src:	stm_source device
818  * @stm:	stm device
819  *
820  * This function establishes a link from stm_source to an stm device so that
821  * the former can send out trace data to the latter.
822  *
823  * Return:	0 on success, -errno otherwise.
824  */
825 static int stm_source_link_add(struct stm_source_device *src,
826 			       struct stm_device *stm)
827 {
828 	char *id;
829 	int err;
830 
831 	mutex_lock(&stm->link_mutex);
832 	spin_lock(&stm->link_lock);
833 	spin_lock(&src->link_lock);
834 
835 	/* src->link is dereferenced under stm_source_srcu but not the list */
836 	rcu_assign_pointer(src->link, stm);
837 	list_add_tail(&src->link_entry, &stm->link_list);
838 
839 	spin_unlock(&src->link_lock);
840 	spin_unlock(&stm->link_lock);
841 	mutex_unlock(&stm->link_mutex);
842 
843 	id = kstrdup(src->data->name, GFP_KERNEL);
844 	if (id) {
845 		src->policy_node =
846 			stp_policy_node_lookup(stm, id);
847 
848 		kfree(id);
849 	}
850 
851 	err = stm_output_assign(stm, src->data->nr_chans,
852 				src->policy_node, &src->output);
853 
854 	if (src->policy_node)
855 		stp_policy_node_put(src->policy_node);
856 
857 	if (err)
858 		goto fail_detach;
859 
860 	/* this is to notify the STM device that a new link has been made */
861 	if (stm->data->link)
862 		err = stm->data->link(stm->data, src->output.master,
863 				      src->output.channel);
864 
865 	if (err)
866 		goto fail_free_output;
867 
868 	/* this is to let the source carry out all necessary preparations */
869 	if (src->data->link)
870 		src->data->link(src->data);
871 
872 	return 0;
873 
874 fail_free_output:
875 	stm_output_free(stm, &src->output);
876 
877 fail_detach:
878 	mutex_lock(&stm->link_mutex);
879 	spin_lock(&stm->link_lock);
880 	spin_lock(&src->link_lock);
881 
882 	rcu_assign_pointer(src->link, NULL);
883 	list_del_init(&src->link_entry);
884 
885 	spin_unlock(&src->link_lock);
886 	spin_unlock(&stm->link_lock);
887 	mutex_unlock(&stm->link_mutex);
888 
889 	return err;
890 }
891 
892 /**
893  * __stm_source_link_drop() - detach stm_source from an stm device
894  * @src:	stm_source device
895  * @stm:	stm device
896  *
897  * If @stm is @src::link, disconnect them from one another and put the
898  * reference on the @stm device.
899  *
900  * Caller must hold stm::link_mutex.
901  */
902 static int __stm_source_link_drop(struct stm_source_device *src,
903 				  struct stm_device *stm)
904 {
905 	struct stm_device *link;
906 	int ret = 0;
907 
908 	lockdep_assert_held(&stm->link_mutex);
909 
910 	/* for stm::link_list modification, we hold both mutex and spinlock */
911 	spin_lock(&stm->link_lock);
912 	spin_lock(&src->link_lock);
913 	link = srcu_dereference_check(src->link, &stm_source_srcu, 1);
914 
915 	/*
916 	 * The linked device may have changed since we last looked, because
917 	 * we weren't holding the src::link_lock back then; if this is the
918 	 * case, tell the caller to retry.
919 	 */
920 	if (link != stm) {
921 		ret = -EAGAIN;
922 		goto unlock;
923 	}
924 
925 	stm_output_free(link, &src->output);
926 	list_del_init(&src->link_entry);
927 	pm_runtime_mark_last_busy(&link->dev);
928 	pm_runtime_put_autosuspend(&link->dev);
929 	/* matches stm_find_device() from stm_source_link_store() */
930 	stm_put_device(link);
931 	rcu_assign_pointer(src->link, NULL);
932 
933 unlock:
934 	spin_unlock(&src->link_lock);
935 	spin_unlock(&stm->link_lock);
936 
937 	/*
938 	 * Call the unlink callbacks for both source and stm, when we know
939 	 * that we have actually performed the unlinking.
940 	 */
941 	if (!ret) {
942 		if (src->data->unlink)
943 			src->data->unlink(src->data);
944 
945 		if (stm->data->unlink)
946 			stm->data->unlink(stm->data, src->output.master,
947 					  src->output.channel);
948 	}
949 
950 	return ret;
951 }
952 
953 /**
954  * stm_source_link_drop() - detach stm_source from its stm device
955  * @src:	stm_source device
956  *
957  * Unlinking means disconnecting from source's STM device; after this
958  * writes will be unsuccessful until it is linked to a new STM device.
959  *
960  * This will happen on "stm_source_link" sysfs attribute write to undo
961  * the existing link (if any), or on linked STM device's de-registration.
962  */
963 static void stm_source_link_drop(struct stm_source_device *src)
964 {
965 	struct stm_device *stm;
966 	int idx, ret;
967 
968 retry:
969 	idx = srcu_read_lock(&stm_source_srcu);
970 	/*
971 	 * The stm device will be valid for the duration of this
972 	 * read section, but the link may change before we grab
973 	 * the src::link_lock in __stm_source_link_drop().
974 	 */
975 	stm = srcu_dereference(src->link, &stm_source_srcu);
976 
977 	ret = 0;
978 	if (stm) {
979 		mutex_lock(&stm->link_mutex);
980 		ret = __stm_source_link_drop(src, stm);
981 		mutex_unlock(&stm->link_mutex);
982 	}
983 
984 	srcu_read_unlock(&stm_source_srcu, idx);
985 
986 	/* if it did change, retry */
987 	if (ret == -EAGAIN)
988 		goto retry;
989 }
990 
991 static ssize_t stm_source_link_show(struct device *dev,
992 				    struct device_attribute *attr,
993 				    char *buf)
994 {
995 	struct stm_source_device *src = to_stm_source_device(dev);
996 	struct stm_device *stm;
997 	int idx, ret;
998 
999 	idx = srcu_read_lock(&stm_source_srcu);
1000 	stm = srcu_dereference(src->link, &stm_source_srcu);
1001 	ret = sprintf(buf, "%s\n",
1002 		      stm ? dev_name(&stm->dev) : "<none>");
1003 	srcu_read_unlock(&stm_source_srcu, idx);
1004 
1005 	return ret;
1006 }
1007 
1008 static ssize_t stm_source_link_store(struct device *dev,
1009 				     struct device_attribute *attr,
1010 				     const char *buf, size_t count)
1011 {
1012 	struct stm_source_device *src = to_stm_source_device(dev);
1013 	struct stm_device *link;
1014 	int err;
1015 
1016 	stm_source_link_drop(src);
1017 
1018 	link = stm_find_device(buf);
1019 	if (!link)
1020 		return -EINVAL;
1021 
1022 	pm_runtime_get(&link->dev);
1023 
1024 	err = stm_source_link_add(src, link);
1025 	if (err) {
1026 		pm_runtime_put_autosuspend(&link->dev);
1027 		/* matches the stm_find_device() above */
1028 		stm_put_device(link);
1029 	}
1030 
1031 	return err ? : count;
1032 }
1033 
1034 static DEVICE_ATTR_RW(stm_source_link);
1035 
1036 static struct attribute *stm_source_attrs[] = {
1037 	&dev_attr_stm_source_link.attr,
1038 	NULL,
1039 };
1040 
1041 ATTRIBUTE_GROUPS(stm_source);
1042 
1043 static struct class stm_source_class = {
1044 	.name		= "stm_source",
1045 	.dev_groups	= stm_source_groups,
1046 };
1047 
1048 static void stm_source_device_release(struct device *dev)
1049 {
1050 	struct stm_source_device *src = to_stm_source_device(dev);
1051 
1052 	kfree(src);
1053 }
1054 
1055 /**
1056  * stm_source_register_device() - register an stm_source device
1057  * @parent:	parent device
1058  * @data:	device description structure
1059  *
1060  * This will create a device of stm_source class that can write
1061  * data to an stm device once linked.
1062  *
1063  * Return:	0 on success, -errno otherwise.
1064  */
1065 int stm_source_register_device(struct device *parent,
1066 			       struct stm_source_data *data)
1067 {
1068 	struct stm_source_device *src;
1069 	int err;
1070 
1071 	if (!stm_core_up)
1072 		return -EPROBE_DEFER;
1073 
1074 	src = kzalloc(sizeof(*src), GFP_KERNEL);
1075 	if (!src)
1076 		return -ENOMEM;
1077 
1078 	device_initialize(&src->dev);
1079 	src->dev.class = &stm_source_class;
1080 	src->dev.parent = parent;
1081 	src->dev.release = stm_source_device_release;
1082 
1083 	err = kobject_set_name(&src->dev.kobj, "%s", data->name);
1084 	if (err)
1085 		goto err;
1086 
1087 	pm_runtime_no_callbacks(&src->dev);
1088 	pm_runtime_forbid(&src->dev);
1089 
1090 	err = device_add(&src->dev);
1091 	if (err)
1092 		goto err;
1093 
1094 	stm_output_init(&src->output);
1095 	spin_lock_init(&src->link_lock);
1096 	INIT_LIST_HEAD(&src->link_entry);
1097 	src->data = data;
1098 	data->src = src;
1099 
1100 	return 0;
1101 
1102 err:
1103 	put_device(&src->dev);
1104 	kfree(src);
1105 
1106 	return err;
1107 }
1108 EXPORT_SYMBOL_GPL(stm_source_register_device);
1109 
1110 /**
1111  * stm_source_unregister_device() - unregister an stm_source device
1112  * @data:	device description that was used to register the device
1113  *
1114  * This will remove a previously created stm_source device from the system.
1115  */
1116 void stm_source_unregister_device(struct stm_source_data *data)
1117 {
1118 	struct stm_source_device *src = data->src;
1119 
1120 	stm_source_link_drop(src);
1121 
1122 	device_unregister(&src->dev);
1123 }
1124 EXPORT_SYMBOL_GPL(stm_source_unregister_device);
1125 
1126 int notrace stm_source_write(struct stm_source_data *data,
1127 			     unsigned int chan,
1128 			     const char *buf, size_t count)
1129 {
1130 	struct stm_source_device *src = data->src;
1131 	struct stm_device *stm;
1132 	int idx;
1133 
1134 	if (!src->output.nr_chans)
1135 		return -ENODEV;
1136 
1137 	if (chan >= src->output.nr_chans)
1138 		return -EINVAL;
1139 
1140 	idx = srcu_read_lock(&stm_source_srcu);
1141 
1142 	stm = srcu_dereference(src->link, &stm_source_srcu);
1143 	if (stm)
1144 		count = stm_write(stm->data, src->output.master,
1145 				  src->output.channel + chan,
1146 				  buf, count);
1147 	else
1148 		count = -ENODEV;
1149 
1150 	srcu_read_unlock(&stm_source_srcu, idx);
1151 
1152 	return count;
1153 }
1154 EXPORT_SYMBOL_GPL(stm_source_write);
1155 
1156 static int __init stm_core_init(void)
1157 {
1158 	int err;
1159 
1160 	err = class_register(&stm_class);
1161 	if (err)
1162 		return err;
1163 
1164 	err = class_register(&stm_source_class);
1165 	if (err)
1166 		goto err_stm;
1167 
1168 	err = stp_configfs_init();
1169 	if (err)
1170 		goto err_src;
1171 
1172 	init_srcu_struct(&stm_source_srcu);
1173 
1174 	stm_core_up++;
1175 
1176 	return 0;
1177 
1178 err_src:
1179 	class_unregister(&stm_source_class);
1180 err_stm:
1181 	class_unregister(&stm_class);
1182 
1183 	return err;
1184 }
1185 
1186 module_init(stm_core_init);
1187 
1188 static void __exit stm_core_exit(void)
1189 {
1190 	cleanup_srcu_struct(&stm_source_srcu);
1191 	class_unregister(&stm_source_class);
1192 	class_unregister(&stm_class);
1193 	stp_configfs_exit();
1194 }
1195 
1196 module_exit(stm_core_exit);
1197 
1198 MODULE_LICENSE("GPL v2");
1199 MODULE_DESCRIPTION("System Trace Module device class");
1200 MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");
1201