2 * Copyright (C) 2014 Red Hat
3 * Author: Rob Clark <robdclark@gmail.com>
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:
12 * The above copyright notice and this permission notice shall be included in
13 * all copies or substantial portions of the Software.
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.
25 #include <drm/drm_crtc.h>
26 #include <drm/drm_modeset_lock.h>
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.
38 * For basic principles of ww_mutex, see: Documentation/locking/ww-mutex-design.txt
40 * The basic usage pattern is to:
42 * drm_modeset_acquire_init(&ctx)
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);
54 * drm_modeset_drop_locks(&ctx);
55 * drm_modeset_acquire_fini(&ctx);
59 * drm_modeset_lock_all - take all modeset locks
62 * This function takes all modeset locks, suitable where a more fine-grained
63 * scheme isn't (yet) implemented. Locks must be dropped with
64 * drm_modeset_unlock_all.
66 void drm_modeset_lock_all(struct drm_device
*dev
)
68 struct drm_mode_config
*config
= &dev
->mode_config
;
69 struct drm_modeset_acquire_ctx
*ctx
;
72 ctx
= kzalloc(sizeof(*ctx
), GFP_KERNEL
);
76 mutex_lock(&config
->mutex
);
78 drm_modeset_acquire_init(ctx
, 0);
81 ret
= drm_modeset_lock(&config
->connection_mutex
, ctx
);
84 ret
= drm_modeset_lock_all_crtcs(dev
, ctx
);
88 WARN_ON(config
->acquire_ctx
);
90 /* now we hold the locks, so now that it is safe, stash the
91 * ctx for drm_modeset_unlock_all():
93 config
->acquire_ctx
= ctx
;
95 drm_warn_on_modeset_not_all_locked(dev
);
100 if (ret
== -EDEADLK
) {
101 drm_modeset_backoff(ctx
);
107 EXPORT_SYMBOL(drm_modeset_lock_all
);
110 * drm_modeset_unlock_all - drop all modeset locks
113 * This function drop all modeset locks taken by drm_modeset_lock_all.
115 void drm_modeset_unlock_all(struct drm_device
*dev
)
117 struct drm_mode_config
*config
= &dev
->mode_config
;
118 struct drm_modeset_acquire_ctx
*ctx
= config
->acquire_ctx
;
123 config
->acquire_ctx
= NULL
;
124 drm_modeset_drop_locks(ctx
);
125 drm_modeset_acquire_fini(ctx
);
129 mutex_unlock(&dev
->mode_config
.mutex
);
131 EXPORT_SYMBOL(drm_modeset_unlock_all
);
134 * drm_modeset_lock_crtc - lock crtc with hidden acquire ctx for a plane update
136 * @plane: DRM plane to be updated on @crtc
138 * This function locks the given crtc and plane (which should be either the
139 * primary or cursor plane) using a hidden acquire context. This is necessary so
140 * that drivers internally using the atomic interfaces can grab further locks
141 * with the lock acquire context.
143 * Note that @plane can be NULL, e.g. when the cursor support hasn't yet been
144 * converted to universal planes yet.
146 void drm_modeset_lock_crtc(struct drm_crtc
*crtc
,
147 struct drm_plane
*plane
)
149 struct drm_modeset_acquire_ctx
*ctx
;
152 ctx
= kzalloc(sizeof(*ctx
), GFP_KERNEL
);
156 drm_modeset_acquire_init(ctx
, 0);
159 ret
= drm_modeset_lock(&crtc
->mutex
, ctx
);
164 ret
= drm_modeset_lock(&plane
->mutex
, ctx
);
169 ret
= drm_modeset_lock(&plane
->crtc
->mutex
, ctx
);
175 WARN_ON(crtc
->acquire_ctx
);
177 /* now we hold the locks, so now that it is safe, stash the
178 * ctx for drm_modeset_unlock_crtc():
180 crtc
->acquire_ctx
= ctx
;
185 if (ret
== -EDEADLK
) {
186 drm_modeset_backoff(ctx
);
190 EXPORT_SYMBOL(drm_modeset_lock_crtc
);
193 * drm_modeset_legacy_acquire_ctx - find acquire ctx for legacy ioctls
196 * Legacy ioctl operations like cursor updates or page flips only have per-crtc
197 * locking, and store the acquire ctx in the corresponding crtc. All other
198 * legacy operations take all locks and use a global acquire context. This
199 * function grabs the right one.
201 struct drm_modeset_acquire_ctx
*
202 drm_modeset_legacy_acquire_ctx(struct drm_crtc
*crtc
)
204 if (crtc
->acquire_ctx
)
205 return crtc
->acquire_ctx
;
207 WARN_ON(!crtc
->dev
->mode_config
.acquire_ctx
);
209 return crtc
->dev
->mode_config
.acquire_ctx
;
211 EXPORT_SYMBOL(drm_modeset_legacy_acquire_ctx
);
214 * drm_modeset_unlock_crtc - drop crtc lock
217 * This drops the crtc lock acquire with drm_modeset_lock_crtc() and all other
218 * locks acquired through the hidden context.
220 void drm_modeset_unlock_crtc(struct drm_crtc
*crtc
)
222 struct drm_modeset_acquire_ctx
*ctx
= crtc
->acquire_ctx
;
227 crtc
->acquire_ctx
= NULL
;
228 drm_modeset_drop_locks(ctx
);
229 drm_modeset_acquire_fini(ctx
);
233 EXPORT_SYMBOL(drm_modeset_unlock_crtc
);
236 * drm_warn_on_modeset_not_all_locked - check that all modeset locks are locked
239 * Useful as a debug assert.
241 void drm_warn_on_modeset_not_all_locked(struct drm_device
*dev
)
243 struct drm_crtc
*crtc
;
245 /* Locking is currently fubar in the panic handler. */
247 if (oops_in_progress
)
251 drm_for_each_crtc(crtc
, dev
)
252 WARN_ON(!drm_modeset_is_locked(&crtc
->mutex
));
254 WARN_ON(!drm_modeset_is_locked(&dev
->mode_config
.connection_mutex
));
255 WARN_ON(!mutex_is_locked(&dev
->mode_config
.mutex
));
257 EXPORT_SYMBOL(drm_warn_on_modeset_not_all_locked
);
260 * drm_modeset_acquire_init - initialize acquire context
261 * @ctx: the acquire context
264 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx
*ctx
,
267 memset(ctx
, 0, sizeof(*ctx
));
268 ww_acquire_init(&ctx
->ww_ctx
, &crtc_ww_class
);
269 INIT_LIST_HEAD(&ctx
->locked
);
271 EXPORT_SYMBOL(drm_modeset_acquire_init
);
274 * drm_modeset_acquire_fini - cleanup acquire context
275 * @ctx: the acquire context
277 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx
*ctx
)
279 ww_acquire_fini(&ctx
->ww_ctx
);
281 EXPORT_SYMBOL(drm_modeset_acquire_fini
);
284 * drm_modeset_drop_locks - drop all locks
285 * @ctx: the acquire context
287 * Drop all locks currently held against this acquire context.
289 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx
*ctx
)
291 WARN_ON(ctx
->contended
);
292 while (!list_empty(&ctx
->locked
)) {
293 struct drm_modeset_lock_info
*info
;
295 info
= list_first_entry(&ctx
->locked
,
296 struct drm_modeset_lock_info
, ctx_entry
);
298 drm_modeset_unlock(info
->lock
);
301 EXPORT_SYMBOL(drm_modeset_drop_locks
);
303 static inline int modeset_lock(struct drm_modeset_lock
*lock
,
304 struct drm_modeset_acquire_ctx
*ctx
,
305 bool interruptible
, bool slow
)
309 WARN_ON(ctx
->contended
);
311 if (ctx
->trylock_only
) {
312 if (!ww_mutex_trylock(&lock
->mutex
))
316 } else if (interruptible
&& slow
) {
317 ret
= ww_mutex_lock_slow_interruptible(&lock
->mutex
, &ctx
->ww_ctx
);
318 } else if (interruptible
) {
319 ret
= ww_mutex_lock_interruptible(&lock
->mutex
, &ctx
->ww_ctx
);
321 ww_mutex_lock_slow(&lock
->mutex
, &ctx
->ww_ctx
);
324 ret
= ww_mutex_lock(&lock
->mutex
, &ctx
->ww_ctx
);
326 if (ret
== -EALREADY
) {
327 /* we already hold the lock.. this is fine. For atomic
328 * we will need to be able to drm_modeset_lock() things
329 * without having to keep track of what is already locked
333 } else if (ret
== -EDEADLK
) {
334 ctx
->contended
= lock
;
337 struct drm_modeset_lock_info
*info
;
339 info
= kzalloc(sizeof(*info
), GFP_KERNEL
);
340 INIT_LIST_HEAD(&info
->ctx_entry
);
341 INIT_LIST_HEAD(&info
->lock_entry
);
344 list_add(&info
->ctx_entry
, &ctx
->locked
);
345 list_add(&info
->lock_entry
, &lock
->locked
);
351 static int modeset_backoff(struct drm_modeset_acquire_ctx
*ctx
,
354 struct drm_modeset_lock
*contended
= ctx
->contended
;
356 ctx
->contended
= NULL
;
358 if (WARN_ON(!contended
))
361 drm_modeset_drop_locks(ctx
);
363 return modeset_lock(contended
, ctx
, interruptible
, true);
367 * drm_modeset_backoff - deadlock avoidance backoff
368 * @ctx: the acquire context
370 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
371 * you must call this function to drop all currently held locks and
372 * block until the contended lock becomes available.
374 void drm_modeset_backoff(struct drm_modeset_acquire_ctx
*ctx
)
376 modeset_backoff(ctx
, false);
378 EXPORT_SYMBOL(drm_modeset_backoff
);
381 * drm_modeset_backoff_interruptible - deadlock avoidance backoff
382 * @ctx: the acquire context
384 * Interruptible version of drm_modeset_backoff()
386 int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx
*ctx
)
388 return modeset_backoff(ctx
, true);
390 EXPORT_SYMBOL(drm_modeset_backoff_interruptible
);
393 * drm_modeset_lock - take modeset lock
394 * @lock: lock to take
397 * If ctx is not NULL, then its ww acquire context is used and the
398 * lock will be tracked by the context and can be released by calling
399 * drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
400 * deadlock scenario has been detected and it is an error to attempt
401 * to take any more locks without first calling drm_modeset_backoff().
403 int drm_modeset_lock(struct drm_modeset_lock
*lock
,
404 struct drm_modeset_acquire_ctx
*ctx
)
407 return modeset_lock(lock
, ctx
, false, false);
409 ww_mutex_lock(&lock
->mutex
, NULL
);
412 EXPORT_SYMBOL(drm_modeset_lock
);
415 * drm_modeset_lock_interruptible - take modeset lock
416 * @lock: lock to take
419 * Interruptible version of drm_modeset_lock()
421 int drm_modeset_lock_interruptible(struct drm_modeset_lock
*lock
,
422 struct drm_modeset_acquire_ctx
*ctx
)
425 return modeset_lock(lock
, ctx
, true, false);
427 return ww_mutex_lock_interruptible(&lock
->mutex
, NULL
);
429 EXPORT_SYMBOL(drm_modeset_lock_interruptible
);
432 * drm_modeset_unlock - drop modeset lock
433 * @lock: lock to release
435 void drm_modeset_unlock(struct drm_modeset_lock
*lock
)
437 struct drm_modeset_lock_info
*info
;
439 /* undo in reverse order */
440 if (!list_empty(&lock
->locked
)) {
441 info
= list_last_entry(&lock
->locked
,
442 struct drm_modeset_lock_info
, lock_entry
);
443 list_del_init(&info
->lock_entry
);
445 list_del_init(&info
->ctx_entry
);
448 ww_mutex_unlock(&lock
->mutex
);
450 EXPORT_SYMBOL(drm_modeset_unlock
);
452 /* In some legacy codepaths it's convenient to just grab all the crtc and plane
454 int drm_modeset_lock_all_crtcs(struct drm_device
*dev
,
455 struct drm_modeset_acquire_ctx
*ctx
)
457 struct drm_crtc
*crtc
;
458 struct drm_plane
*plane
;
461 drm_for_each_crtc(crtc
, dev
) {
462 ret
= drm_modeset_lock(&crtc
->mutex
, ctx
);
467 drm_for_each_plane(plane
, dev
) {
468 ret
= drm_modeset_lock(&plane
->mutex
, ctx
);
475 EXPORT_SYMBOL(drm_modeset_lock_all_crtcs
);