1/*
2 * Copyright (C) 2014 Red Hat
3 * Author: Rob Clark <robdclark@gmail.com>
4 *
5 * Permission is hereby granted, free of charge, to any person obtaining a
6 * copy of this software and associated documentation files (the "Software"),
7 * to deal in the Software without restriction, including without limitation
8 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
9 * and/or sell copies of the Software, and to permit persons to whom the
10 * Software is furnished to do so, subject to the following conditions:
11 *
12 * The above copyright notice and this permission notice shall be included in
13 * all copies or substantial portions of the Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
19 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
20 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
21 * OTHER DEALINGS IN THE SOFTWARE.
22 */
23
24#include <drm/drmP.h>
25#include <drm/drm_crtc.h>
26#include <drm/drm_modeset_lock.h>
27
28/**
29 * DOC: kms locking
30 *
31 * As KMS moves toward more fine grained locking, and atomic ioctl where
32 * userspace can indirectly control locking order, it becomes necessary
33 * to use ww_mutex and acquire-contexts to avoid deadlocks.  But because
34 * the locking is more distributed around the driver code, we want a bit
35 * of extra utility/tracking out of our acquire-ctx.  This is provided
36 * by drm_modeset_lock / drm_modeset_acquire_ctx.
37 *
38 * For basic principles of ww_mutex, see: Documentation/locking/ww-mutex-design.txt
39 *
40 * The basic usage pattern is to:
41 *
42 *     drm_modeset_acquire_init(&ctx)
43 *   retry:
44 *     foreach (lock in random_ordered_set_of_locks) {
45 *       ret = drm_modeset_lock(lock, &ctx)
46 *       if (ret == -EDEADLK) {
47 *          drm_modeset_backoff(&ctx);
48 *          goto retry;
49 *       }
50 *     }
51 *
52 *     ... do stuff ...
53 *
54 *     drm_modeset_drop_locks(&ctx);
55 *     drm_modeset_acquire_fini(&ctx);
56 */
57
58
59/**
60 * __drm_modeset_lock_all - internal helper to grab all modeset locks
61 * @dev: DRM device
62 * @trylock: trylock mode for atomic contexts
63 *
64 * This is a special version of drm_modeset_lock_all() which can also be used in
65 * atomic contexts. Then @trylock must be set to true.
66 *
67 * Returns:
68 * 0 on success or negative error code on failure.
69 */
70int __drm_modeset_lock_all(struct drm_device *dev,
71			   bool trylock)
72{
73	struct drm_mode_config *config = &dev->mode_config;
74	struct drm_modeset_acquire_ctx *ctx;
75	int ret;
76
77	ctx = kzalloc(sizeof(*ctx),
78		      trylock ? GFP_ATOMIC : GFP_KERNEL);
79	if (!ctx)
80		return -ENOMEM;
81
82	if (trylock) {
83		if (!mutex_trylock(&config->mutex))
84			return -EBUSY;
85	} else {
86		mutex_lock(&config->mutex);
87	}
88
89	drm_modeset_acquire_init(ctx, 0);
90	ctx->trylock_only = trylock;
91
92retry:
93	ret = drm_modeset_lock(&config->connection_mutex, ctx);
94	if (ret)
95		goto fail;
96	ret = drm_modeset_lock_all_crtcs(dev, ctx);
97	if (ret)
98		goto fail;
99
100	WARN_ON(config->acquire_ctx);
101
102	/* now we hold the locks, so now that it is safe, stash the
103	 * ctx for drm_modeset_unlock_all():
104	 */
105	config->acquire_ctx = ctx;
106
107	drm_warn_on_modeset_not_all_locked(dev);
108
109	return 0;
110
111fail:
112	if (ret == -EDEADLK) {
113		drm_modeset_backoff(ctx);
114		goto retry;
115	}
116
117	return ret;
118}
119EXPORT_SYMBOL(__drm_modeset_lock_all);
120
121/**
122 * drm_modeset_lock_all - take all modeset locks
123 * @dev: drm device
124 *
125 * This function takes all modeset locks, suitable where a more fine-grained
126 * scheme isn't (yet) implemented. Locks must be dropped with
127 * drm_modeset_unlock_all.
128 */
129void drm_modeset_lock_all(struct drm_device *dev)
130{
131	WARN_ON(__drm_modeset_lock_all(dev, false) != 0);
132}
133EXPORT_SYMBOL(drm_modeset_lock_all);
134
135/**
136 * drm_modeset_unlock_all - drop all modeset locks
137 * @dev: device
138 *
139 * This function drop all modeset locks taken by drm_modeset_lock_all.
140 */
141void drm_modeset_unlock_all(struct drm_device *dev)
142{
143	struct drm_mode_config *config = &dev->mode_config;
144	struct drm_modeset_acquire_ctx *ctx = config->acquire_ctx;
145
146	if (WARN_ON(!ctx))
147		return;
148
149	config->acquire_ctx = NULL;
150	drm_modeset_drop_locks(ctx);
151	drm_modeset_acquire_fini(ctx);
152
153	kfree(ctx);
154
155	mutex_unlock(&dev->mode_config.mutex);
156}
157EXPORT_SYMBOL(drm_modeset_unlock_all);
158
159/**
160 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
161 * @crtc: DRM CRTC
162 * @plane: DRM plane to be updated on @crtc
163 *
164 * This function locks the given crtc and plane (which should be either the
165 * primary or cursor plane) using a hidden acquire context. This is necessary so
166 * that drivers internally using the atomic interfaces can grab further locks
167 * with the lock acquire context.
168 *
169 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
170 * converted to universal planes yet.
171 */
172void drm_modeset_lock_crtc(struct drm_crtc *crtc,
173			   struct drm_plane *plane)
174{
175	struct drm_modeset_acquire_ctx *ctx;
176	int ret;
177
178	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
179	if (WARN_ON(!ctx))
180		return;
181
182	drm_modeset_acquire_init(ctx, 0);
183
184retry:
185	ret = drm_modeset_lock(&crtc->mutex, ctx);
186	if (ret)
187		goto fail;
188
189	if (plane) {
190		ret = drm_modeset_lock(&plane->mutex, ctx);
191		if (ret)
192			goto fail;
193
194		if (plane->crtc) {
195			ret = drm_modeset_lock(&plane->crtc->mutex, ctx);
196			if (ret)
197				goto fail;
198		}
199	}
200
201	WARN_ON(crtc->acquire_ctx);
202
203	/* now we hold the locks, so now that it is safe, stash the
204	 * ctx for drm_modeset_unlock_crtc():
205	 */
206	crtc->acquire_ctx = ctx;
207
208	return;
209
210fail:
211	if (ret == -EDEADLK) {
212		drm_modeset_backoff(ctx);
213		goto retry;
214	}
215}
216EXPORT_SYMBOL(drm_modeset_lock_crtc);
217
218/**
219 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
220 * @crtc: drm crtc
221 *
222 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
223 * locking, and store the acquire ctx in the corresponding crtc. All other
224 * legacy operations take all locks and use a global acquire context. This
225 * function grabs the right one.
226 */
227struct drm_modeset_acquire_ctx *
228drm_modeset_legacy_acquire_ctx(struct drm_crtc *crtc)
229{
230	if (crtc->acquire_ctx)
231		return crtc->acquire_ctx;
232
233	WARN_ON(!crtc->dev->mode_config.acquire_ctx);
234
235	return crtc->dev->mode_config.acquire_ctx;
236}
237EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx);
238
239/**
240 * drm_modeset_unlock_crtc - drop crtc lock
241 * @crtc: drm crtc
242 *
243 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
244 * locks acquired through the hidden context.
245 */
246void drm_modeset_unlock_crtc(struct drm_crtc *crtc)
247{
248	struct drm_modeset_acquire_ctx *ctx = crtc->acquire_ctx;
249
250	if (WARN_ON(!ctx))
251		return;
252
253	crtc->acquire_ctx = NULL;
254	drm_modeset_drop_locks(ctx);
255	drm_modeset_acquire_fini(ctx);
256
257	kfree(ctx);
258}
259EXPORT_SYMBOL(drm_modeset_unlock_crtc);
260
261/**
262 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
263 * @dev: device
264 *
265 * Useful as a debug assert.
266 */
267void drm_warn_on_modeset_not_all_locked(struct drm_device *dev)
268{
269	struct drm_crtc *crtc;
270
271	/* Locking is currently fubar in the panic handler. */
272	if (oops_in_progress)
273		return;
274
275	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
276		WARN_ON(!drm_modeset_is_locked(&crtc->mutex));
277
278	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
279	WARN_ON(!mutex_is_locked(&dev->mode_config.mutex));
280}
281EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked);
282
283/**
284 * drm_modeset_acquire_init - initialize acquire context
285 * @ctx: the acquire context
286 * @flags: for future
287 */
288void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
289		uint32_t flags)
290{
291	memset(ctx, 0, sizeof(*ctx));
292	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
293	INIT_LIST_HEAD(&ctx->locked);
294}
295EXPORT_SYMBOL(drm_modeset_acquire_init);
296
297/**
298 * drm_modeset_acquire_fini - cleanup acquire context
299 * @ctx: the acquire context
300 */
301void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
302{
303	ww_acquire_fini(&ctx->ww_ctx);
304}
305EXPORT_SYMBOL(drm_modeset_acquire_fini);
306
307/**
308 * drm_modeset_drop_locks - drop all locks
309 * @ctx: the acquire context
310 *
311 * Drop all locks currently held against this acquire context.
312 */
313void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
314{
315	WARN_ON(ctx->contended);
316	while (!list_empty(&ctx->locked)) {
317		struct drm_modeset_lock *lock;
318
319		lock = list_first_entry(&ctx->locked,
320				struct drm_modeset_lock, head);
321
322		drm_modeset_unlock(lock);
323	}
324}
325EXPORT_SYMBOL(drm_modeset_drop_locks);
326
327static inline int modeset_lock(struct drm_modeset_lock *lock,
328		struct drm_modeset_acquire_ctx *ctx,
329		bool interruptible, bool slow)
330{
331	int ret;
332
333	WARN_ON(ctx->contended);
334
335	if (ctx->trylock_only) {
336		if (!ww_mutex_trylock(&lock->mutex))
337			return -EBUSY;
338		else
339			return 0;
340	} else if (interruptible && slow) {
341		ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
342	} else if (interruptible) {
343		ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
344	} else if (slow) {
345		ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
346		ret = 0;
347	} else {
348		ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
349	}
350	if (!ret) {
351		WARN_ON(!list_empty(&lock->head));
352		list_add(&lock->head, &ctx->locked);
353	} else if (ret == -EALREADY) {
354		/* we already hold the lock.. this is fine.  For atomic
355		 * we will need to be able to drm_modeset_lock() things
356		 * without having to keep track of what is already locked
357		 * or not.
358		 */
359		ret = 0;
360	} else if (ret == -EDEADLK) {
361		ctx->contended = lock;
362	}
363
364	return ret;
365}
366
367static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
368		bool interruptible)
369{
370	struct drm_modeset_lock *contended = ctx->contended;
371
372	ctx->contended = NULL;
373
374	if (WARN_ON(!contended))
375		return 0;
376
377	drm_modeset_drop_locks(ctx);
378
379	return modeset_lock(contended, ctx, interruptible, true);
380}
381
382/**
383 * drm_modeset_backoff - deadlock avoidance backoff
384 * @ctx: the acquire context
385 *
386 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
387 * you must call this function to drop all currently held locks and
388 * block until the contended lock becomes available.
389 */
390void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
391{
392	modeset_backoff(ctx, false);
393}
394EXPORT_SYMBOL(drm_modeset_backoff);
395
396/**
397 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
398 * @ctx: the acquire context
399 *
400 * Interruptible version of drm_modeset_backoff()
401 */
402int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
403{
404	return modeset_backoff(ctx, true);
405}
406EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
407
408/**
409 * drm_modeset_lock - take modeset lock
410 * @lock: lock to take
411 * @ctx: acquire ctx
412 *
413 * If ctx is not NULL, then its ww acquire context is used and the
414 * lock will be tracked by the context and can be released by calling
415 * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
416 * deadlock scenario has been detected and it is an error to attempt
417 * to take any more locks without first calling drm_modeset_backoff().
418 */
419int drm_modeset_lock(struct drm_modeset_lock *lock,
420		struct drm_modeset_acquire_ctx *ctx)
421{
422	if (ctx)
423		return modeset_lock(lock, ctx, false, false);
424
425	ww_mutex_lock(&lock->mutex, NULL);
426	return 0;
427}
428EXPORT_SYMBOL(drm_modeset_lock);
429
430/**
431 * drm_modeset_lock_interruptible - take modeset lock
432 * @lock: lock to take
433 * @ctx: acquire ctx
434 *
435 * Interruptible version of drm_modeset_lock()
436 */
437int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
438		struct drm_modeset_acquire_ctx *ctx)
439{
440	if (ctx)
441		return modeset_lock(lock, ctx, true, false);
442
443	return ww_mutex_lock_interruptible(&lock->mutex, NULL);
444}
445EXPORT_SYMBOL(drm_modeset_lock_interruptible);
446
447/**
448 * drm_modeset_unlock - drop modeset lock
449 * @lock: lock to release
450 */
451void drm_modeset_unlock(struct drm_modeset_lock *lock)
452{
453	list_del_init(&lock->head);
454	ww_mutex_unlock(&lock->mutex);
455}
456EXPORT_SYMBOL(drm_modeset_unlock);
457
458/* In some legacy codepaths it's convenient to just grab all the crtc and plane
459 * related locks. */
460int drm_modeset_lock_all_crtcs(struct drm_device *dev,
461		struct drm_modeset_acquire_ctx *ctx)
462{
463	struct drm_mode_config *config = &dev->mode_config;
464	struct drm_crtc *crtc;
465	struct drm_plane *plane;
466	int ret = 0;
467
468	list_for_each_entry(crtc, &config->crtc_list, head) {
469		ret = drm_modeset_lock(&crtc->mutex, ctx);
470		if (ret)
471			return ret;
472	}
473
474	list_for_each_entry(plane, &config->plane_list, head) {
475		ret = drm_modeset_lock(&plane->mutex, ctx);
476		if (ret)
477			return ret;
478	}
479
480	return 0;
481}
482EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);
483