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 #ifndef DRM_MODESET_LOCK_H_
25 #define DRM_MODESET_LOCK_H_
26 
27 #include <linux/types.h> /* stackdepot.h is not self-contained */
28 #include <linux/stackdepot.h>
29 #include <linux/ww_mutex.h>
30 
31 struct drm_modeset_lock;
32 
33 /**
34  * struct drm_modeset_acquire_ctx - locking context (see ww_acquire_ctx)
35  * @ww_ctx: base acquire ctx
36  * @contended: used internally for -EDEADLK handling
37  * @stack_depot: used internally for contention debugging
38  * @locked: list of held locks
39  * @trylock_only: trylock mode used in atomic contexts/panic notifiers
40  * @interruptible: whether interruptible locking should be used.
41  *
42  * Each thread competing for a set of locks must use one acquire
43  * ctx.  And if any lock fxn returns -EDEADLK, it must backoff and
44  * retry.
45  */
46 struct drm_modeset_acquire_ctx {
47 
48 	struct ww_acquire_ctx ww_ctx;
49 
50 	/*
51 	 * Contended lock: if a lock is contended you should only call
52 	 * drm_modeset_backoff() which drops locks and slow-locks the
53 	 * contended lock.
54 	 */
55 	struct drm_modeset_lock *contended;
56 
57 	/*
58 	 * Stack depot for debugging when a contended lock was not backed off
59 	 * from.
60 	 */
61 	depot_stack_handle_t stack_depot;
62 
63 	/*
64 	 * list of held locks (drm_modeset_lock)
65 	 */
66 	struct list_head locked;
67 
68 	/*
69 	 * Trylock mode, use only for panic handlers!
70 	 */
71 	bool trylock_only;
72 
73 	/* Perform interruptible waits on this context. */
74 	bool interruptible;
75 };
76 
77 /**
78  * struct drm_modeset_lock - used for locking modeset resources.
79  * @mutex: resource locking
80  * @head: used to hold its place on &drm_atomi_state.locked list when
81  *    part of an atomic update
82  *
83  * Used for locking CRTCs and other modeset resources.
84  */
85 struct drm_modeset_lock {
86 	/*
87 	 * modeset lock
88 	 */
89 	struct ww_mutex mutex;
90 
91 	/*
92 	 * Resources that are locked as part of an atomic update are added
93 	 * to a list (so we know what to unlock at the end).
94 	 */
95 	struct list_head head;
96 };
97 
98 #define DRM_MODESET_ACQUIRE_INTERRUPTIBLE BIT(0)
99 
100 void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
101 		uint32_t flags);
102 void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx);
103 void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx);
104 int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);
105 
106 void drm_modeset_lock_init(struct drm_modeset_lock *lock);
107 
108 /**
109  * drm_modeset_lock_fini - cleanup lock
110  * @lock: lock to cleanup
111  */
drm_modeset_lock_fini(struct drm_modeset_lock * lock)112 static inline void drm_modeset_lock_fini(struct drm_modeset_lock *lock)
113 {
114 	WARN_ON(!list_empty(&lock->head));
115 }
116 
117 /**
118  * drm_modeset_is_locked - equivalent to mutex_is_locked()
119  * @lock: lock to check
120  */
drm_modeset_is_locked(struct drm_modeset_lock * lock)121 static inline bool drm_modeset_is_locked(struct drm_modeset_lock *lock)
122 {
123 	return ww_mutex_is_locked(&lock->mutex);
124 }
125 
126 /**
127  * drm_modeset_lock_assert_held - equivalent to lockdep_assert_held()
128  * @lock: lock to check
129  */
drm_modeset_lock_assert_held(struct drm_modeset_lock * lock)130 static inline void drm_modeset_lock_assert_held(struct drm_modeset_lock *lock)
131 {
132 	lockdep_assert_held(&lock->mutex.base);
133 }
134 
135 int drm_modeset_lock(struct drm_modeset_lock *lock,
136 		struct drm_modeset_acquire_ctx *ctx);
137 int __must_check drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock);
138 void drm_modeset_unlock(struct drm_modeset_lock *lock);
139 
140 struct drm_device;
141 struct drm_crtc;
142 struct drm_plane;
143 
144 void drm_modeset_lock_all(struct drm_device *dev);
145 void drm_modeset_unlock_all(struct drm_device *dev);
146 void drm_warn_on_modeset_not_all_locked(struct drm_device *dev);
147 
148 int drm_modeset_lock_all_ctx(struct drm_device *dev,
149 			     struct drm_modeset_acquire_ctx *ctx);
150 
151 /**
152  * DRM_MODESET_LOCK_ALL_BEGIN - Helper to acquire modeset locks
153  * @dev: drm device
154  * @ctx: local modeset acquire context, will be dereferenced
155  * @flags: DRM_MODESET_ACQUIRE_* flags to pass to drm_modeset_acquire_init()
156  * @ret: local ret/err/etc variable to track error status
157  *
158  * Use these macros to simplify grabbing all modeset locks using a local
159  * context. This has the advantage of reducing boilerplate, but also properly
160  * checking return values where appropriate.
161  *
162  * Any code run between BEGIN and END will be holding the modeset locks.
163  *
164  * This must be paired with DRM_MODESET_LOCK_ALL_END(). We will jump back and
165  * forth between the labels on deadlock and error conditions.
166  *
167  * Drivers can acquire additional modeset locks. If any lock acquisition
168  * fails, the control flow needs to jump to DRM_MODESET_LOCK_ALL_END() with
169  * the @ret parameter containing the return value of drm_modeset_lock().
170  *
171  * Returns:
172  * The only possible value of ret immediately after DRM_MODESET_LOCK_ALL_BEGIN()
173  * is 0, so no error checking is necessary
174  */
175 #define DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, flags, ret)		\
176 	if (!drm_drv_uses_atomic_modeset(dev))				\
177 		mutex_lock(&dev->mode_config.mutex);			\
178 	drm_modeset_acquire_init(&ctx, flags);				\
179 modeset_lock_retry:							\
180 	ret = drm_modeset_lock_all_ctx(dev, &ctx);			\
181 	if (ret)							\
182 		goto modeset_lock_fail;
183 
184 /**
185  * DRM_MODESET_LOCK_ALL_END - Helper to release and cleanup modeset locks
186  * @dev: drm device
187  * @ctx: local modeset acquire context, will be dereferenced
188  * @ret: local ret/err/etc variable to track error status
189  *
190  * The other side of DRM_MODESET_LOCK_ALL_BEGIN(). It will bounce back to BEGIN
191  * if ret is -EDEADLK.
192  *
193  * It's important that you use the same ret variable for begin and end so
194  * deadlock conditions are properly handled.
195  *
196  * Returns:
197  * ret will be untouched unless it is -EDEADLK on entry. That means that if you
198  * successfully acquire the locks, ret will be whatever your code sets it to. If
199  * there is a deadlock or other failure with acquire or backoff, ret will be set
200  * to that failure. In both of these cases the code between BEGIN/END will not
201  * be run, so the failure will reflect the inability to grab the locks.
202  */
203 #define DRM_MODESET_LOCK_ALL_END(dev, ctx, ret)				\
204 modeset_lock_fail:							\
205 	if (ret == -EDEADLK) {						\
206 		ret = drm_modeset_backoff(&ctx);			\
207 		if (!ret)						\
208 			goto modeset_lock_retry;			\
209 	}								\
210 	drm_modeset_drop_locks(&ctx);					\
211 	drm_modeset_acquire_fini(&ctx);					\
212 	if (!drm_drv_uses_atomic_modeset(dev))				\
213 		mutex_unlock(&dev->mode_config.mutex);
214 
215 #endif /* DRM_MODESET_LOCK_H_ */
216