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