1 | /* $NetBSD: drm_lock.c,v 1.4 2016/04/02 22:40:43 riastradh Exp $ */ |
2 | |
3 | /*- |
4 | * Copyright (c) 2013 The NetBSD Foundation, Inc. |
5 | * All rights reserved. |
6 | * |
7 | * This code is derived from software contributed to The NetBSD Foundation |
8 | * by Taylor R. Campbell. |
9 | * |
10 | * Redistribution and use in source and binary forms, with or without |
11 | * modification, are permitted provided that the following conditions |
12 | * are met: |
13 | * 1. Redistributions of source code must retain the above copyright |
14 | * notice, this list of conditions and the following disclaimer. |
15 | * 2. Redistributions in binary form must reproduce the above copyright |
16 | * notice, this list of conditions and the following disclaimer in the |
17 | * documentation and/or other materials provided with the distribution. |
18 | * |
19 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
20 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
21 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
22 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
23 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
24 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
25 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
26 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
27 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
28 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
29 | * POSSIBILITY OF SUCH DAMAGE. |
30 | */ |
31 | |
32 | /* |
33 | * DRM lock. Each drm master has a heavy-weight lock to provide mutual |
34 | * exclusion for access to the hardware. The lock can be held by the |
35 | * kernel or by a drm file; the kernel takes access only for unusual |
36 | * purposes, with drm_idlelock_take, mainly for idling the GPU when |
37 | * closing down. |
38 | * |
39 | * The physical memory storing the lock state is shared between |
40 | * userland and kernel: the pointer at dev->master->lock->hw_lock is |
41 | * mapped into both userland and kernel address spaces. This way, |
42 | * userland can try to take the hardware lock without a system call, |
43 | * although if it fails then it will use the DRM_LOCK ioctl to block |
44 | * atomically until the lock is available. All this means that the |
45 | * kernel must use atomic_ops to manage the lock state. |
46 | */ |
47 | |
48 | #include <sys/cdefs.h> |
49 | __KERNEL_RCSID(0, "$NetBSD: drm_lock.c,v 1.4 2016/04/02 22:40:43 riastradh Exp $" ); |
50 | |
51 | #include <sys/types.h> |
52 | #include <sys/errno.h> |
53 | #include <sys/systm.h> |
54 | |
55 | #include <drm/drmP.h> |
56 | |
57 | static bool drm_lock_acquire(struct drm_lock_data *, int); |
58 | static void drm_lock_release(struct drm_lock_data *, int); |
59 | static int drm_lock_block_signals(struct drm_device *, struct drm_lock *, |
60 | struct drm_file *); |
61 | static void drm_lock_unblock_signals(struct drm_device *, |
62 | struct drm_lock *, struct drm_file *); |
63 | |
64 | /* |
65 | * Take the lock on behalf of userland. |
66 | */ |
67 | int |
68 | drm_lock(struct drm_device *dev, void *data, struct drm_file *file) |
69 | { |
70 | struct drm_lock *lock_request = data; |
71 | struct drm_master *master = file->master; |
72 | int error; |
73 | |
74 | /* Sanitize the drm global mutex bollocks until we get rid of it. */ |
75 | KASSERT(mutex_is_locked(&drm_global_mutex)); |
76 | mutex_unlock(&drm_global_mutex); |
77 | |
78 | /* Refuse to lock on behalf of the kernel. */ |
79 | if (lock_request->context == DRM_KERNEL_CONTEXT) { |
80 | error = -EINVAL; |
81 | goto out0; |
82 | } |
83 | |
84 | /* Refuse to set the magic bits. */ |
85 | if (lock_request->context != |
86 | _DRM_LOCKING_CONTEXT(lock_request->context)) { |
87 | error = -EINVAL; |
88 | goto out0; |
89 | } |
90 | |
91 | /* Count it in the file and device statistics (XXX why here?). */ |
92 | file->lock_count++; |
93 | |
94 | /* Wait until the hardware lock is gone or we can acquire it. */ |
95 | spin_lock(&master->lock.spinlock); |
96 | |
97 | if (master->lock.user_waiters == UINT32_MAX) { |
98 | error = -EBUSY; |
99 | goto out1; |
100 | } |
101 | |
102 | master->lock.user_waiters++; |
103 | DRM_SPIN_WAIT_UNTIL(error, &master->lock.lock_queue, |
104 | &master->lock.spinlock, |
105 | ((master->lock.hw_lock == NULL) || |
106 | drm_lock_acquire(&master->lock, lock_request->context))); |
107 | KASSERT(0 < master->lock.user_waiters); |
108 | master->lock.user_waiters--; |
109 | if (error) |
110 | goto out1; |
111 | |
112 | /* If the lock is gone, give up. */ |
113 | if (master->lock.hw_lock == NULL) { |
114 | #if 0 /* XXX Linux sends SIGTERM, but why? */ |
115 | mutex_enter(proc_lock); |
116 | psignal(curproc, SIGTERM); |
117 | mutex_exit(proc_lock); |
118 | error = -EINTR; |
119 | #else |
120 | error = -ENXIO; |
121 | #endif |
122 | goto out1; |
123 | } |
124 | |
125 | /* Mark the lock as owned by file. */ |
126 | master->lock.file_priv = file; |
127 | master->lock.lock_time = jiffies; /* XXX Unused? */ |
128 | |
129 | /* Block signals while the lock is held. */ |
130 | error = drm_lock_block_signals(dev, lock_request, file); |
131 | if (error) |
132 | goto fail2; |
133 | |
134 | /* Enter the DMA quiescent state if requested and available. */ |
135 | /* XXX Drop the spin lock first... */ |
136 | if (ISSET(lock_request->flags, _DRM_LOCK_QUIESCENT) && |
137 | (dev->driver->dma_quiescent != NULL)) { |
138 | error = (*dev->driver->dma_quiescent)(dev); |
139 | if (error) |
140 | goto fail3; |
141 | } |
142 | |
143 | /* Success! */ |
144 | error = 0; |
145 | goto out1; |
146 | |
147 | fail3: drm_lock_unblock_signals(dev, lock_request, file); |
148 | fail2: drm_lock_release(&master->lock, lock_request->context); |
149 | master->lock.file_priv = NULL; |
150 | out1: spin_unlock(&master->lock.spinlock); |
151 | out0: mutex_lock(&drm_global_mutex); |
152 | return error; |
153 | } |
154 | |
155 | /* |
156 | * Try to relinquish a lock that userland thinks it holds, per |
157 | * userland's request. Fail if it doesn't actually hold the lock. |
158 | */ |
159 | int |
160 | drm_unlock(struct drm_device *dev, void *data, struct drm_file *file) |
161 | { |
162 | struct drm_lock *lock_request = data; |
163 | struct drm_master *master = file->master; |
164 | int error; |
165 | |
166 | /* Sanitize the drm global mutex bollocks until we get rid of it. */ |
167 | KASSERT(mutex_is_locked(&drm_global_mutex)); |
168 | mutex_unlock(&drm_global_mutex); |
169 | |
170 | /* Refuse to unlock on behalf of the kernel. */ |
171 | if (lock_request->context == DRM_KERNEL_CONTEXT) { |
172 | error = -EINVAL; |
173 | goto out0; |
174 | } |
175 | |
176 | /* Lock the internal spin lock to make changes. */ |
177 | spin_lock(&master->lock.spinlock); |
178 | |
179 | /* Make sure it's actually locked. */ |
180 | if (!_DRM_LOCK_IS_HELD(master->lock.hw_lock->lock)) { |
181 | error = -EINVAL; /* XXX Right error? */ |
182 | goto out1; |
183 | } |
184 | |
185 | /* Make sure it's locked in the right context. */ |
186 | if (_DRM_LOCKING_CONTEXT(master->lock.hw_lock->lock) != |
187 | lock_request->context) { |
188 | error = -EACCES; /* XXX Right error? */ |
189 | goto out1; |
190 | } |
191 | |
192 | /* Make sure it's locked by us. */ |
193 | if (master->lock.file_priv != file) { |
194 | error = -EACCES; /* XXX Right error? */ |
195 | goto out1; |
196 | } |
197 | |
198 | /* Actually release the lock. */ |
199 | drm_lock_release(&master->lock, lock_request->context); |
200 | |
201 | /* Clear the lock's file pointer, just in case. */ |
202 | master->lock.file_priv = NULL; |
203 | |
204 | /* Unblock the signals we blocked in drm_lock. */ |
205 | drm_lock_unblock_signals(dev, lock_request, file); |
206 | |
207 | /* Success! */ |
208 | error = 0; |
209 | |
210 | out1: spin_unlock(&master->lock.spinlock); |
211 | out0: mutex_lock(&drm_global_mutex); |
212 | return error; |
213 | } |
214 | |
215 | /* |
216 | * Drop the lock. |
217 | * |
218 | * Return value is an artefact of Linux. Caller must guarantee |
219 | * preconditions; failure is fatal. |
220 | * |
221 | * XXX Should we also unblock signals like drm_unlock does? |
222 | */ |
223 | int |
224 | drm_lock_free(struct drm_lock_data *lock_data, unsigned int context) |
225 | { |
226 | |
227 | spin_lock(&lock_data->spinlock); |
228 | drm_lock_release(lock_data, context); |
229 | spin_unlock(&lock_data->spinlock); |
230 | |
231 | return 0; |
232 | } |
233 | |
234 | /* |
235 | * Try to acquire the lock. Whether or not we acquire it, guarantee |
236 | * that whoever next releases it relinquishes it to the kernel, not to |
237 | * anyone else. |
238 | */ |
239 | void |
240 | drm_idlelock_take(struct drm_lock_data *lock_data) |
241 | { |
242 | |
243 | spin_lock(&lock_data->spinlock); |
244 | KASSERT(!lock_data->idle_has_lock); |
245 | KASSERT(lock_data->kernel_waiters < UINT32_MAX); |
246 | lock_data->kernel_waiters++; |
247 | /* Try to acquire the lock. */ |
248 | if (drm_lock_acquire(lock_data, DRM_KERNEL_CONTEXT)) { |
249 | lock_data->idle_has_lock = 1; |
250 | } else { |
251 | /* |
252 | * Recording that there are kernel waiters will prevent |
253 | * userland from acquiring the lock again when it is |
254 | * next released. |
255 | */ |
256 | } |
257 | spin_unlock(&lock_data->spinlock); |
258 | } |
259 | |
260 | /* |
261 | * Release whatever drm_idlelock_take managed to acquire. |
262 | */ |
263 | void |
264 | drm_idlelock_release(struct drm_lock_data *lock_data) |
265 | { |
266 | |
267 | spin_lock(&lock_data->spinlock); |
268 | KASSERT(0 < lock_data->kernel_waiters); |
269 | if (--lock_data->kernel_waiters == 0) { |
270 | if (lock_data->idle_has_lock) { |
271 | /* We did acquire it. Release it. */ |
272 | drm_lock_release(lock_data, DRM_KERNEL_CONTEXT); |
273 | } |
274 | } |
275 | spin_unlock(&lock_data->spinlock); |
276 | } |
277 | |
278 | /* |
279 | * Does this file hold this drm device's hardware lock? |
280 | * |
281 | * Used to decide whether to release the lock when the file is being |
282 | * closed. |
283 | * |
284 | * XXX I don't think this answers correctly in the case that the |
285 | * userland has taken the lock and it is uncontended. But I don't |
286 | * think we can know what the correct answer is in that case. |
287 | */ |
288 | int |
289 | drm_i_have_hw_lock(struct drm_device *dev, struct drm_file *file) |
290 | { |
291 | struct drm_lock_data *const lock_data = &file->master->lock; |
292 | int answer = 0; |
293 | |
294 | /* If this file has never locked anything, then no. */ |
295 | if (file->lock_count == 0) |
296 | return 0; |
297 | |
298 | spin_lock(&lock_data->spinlock); |
299 | |
300 | /* If there is no lock, then this file doesn't hold it. */ |
301 | if (lock_data->hw_lock == NULL) |
302 | goto out; |
303 | |
304 | /* If this lock is not held, then this file doesn't hold it. */ |
305 | if (!_DRM_LOCK_IS_HELD(lock_data->hw_lock->lock)) |
306 | goto out; |
307 | |
308 | /* |
309 | * Otherwise, it boils down to whether this file is the owner |
310 | * or someone else. |
311 | * |
312 | * XXX This is not reliable! Userland doesn't update this when |
313 | * it takes the lock... |
314 | */ |
315 | answer = (file == lock_data->file_priv); |
316 | |
317 | out: spin_unlock(&lock_data->spinlock); |
318 | return answer; |
319 | } |
320 | |
321 | /* |
322 | * Try to acquire the lock. Return true if successful, false if not. |
323 | * |
324 | * This is hairy because it races with userland, and if userland |
325 | * already holds the lock, we must tell it, by marking it |
326 | * _DRM_LOCK_CONT (contended), that it must call ioctl(DRM_UNLOCK) to |
327 | * release the lock so that we can wake waiters. |
328 | * |
329 | * XXX What happens if the process is interrupted? |
330 | */ |
331 | static bool |
332 | drm_lock_acquire(struct drm_lock_data *lock_data, int context) |
333 | { |
334 | volatile unsigned int *const lock = &lock_data->hw_lock->lock; |
335 | unsigned int old, new; |
336 | |
337 | KASSERT(spin_is_locked(&lock_data->spinlock)); |
338 | |
339 | do { |
340 | old = *lock; |
341 | if (!_DRM_LOCK_IS_HELD(old)) { |
342 | new = (context | _DRM_LOCK_HELD); |
343 | if ((0 < lock_data->user_waiters) || |
344 | (0 < lock_data->kernel_waiters)) |
345 | new |= _DRM_LOCK_CONT; |
346 | } else if (_DRM_LOCKING_CONTEXT(old) != context) { |
347 | new = (old | _DRM_LOCK_CONT); |
348 | } else { |
349 | DRM_ERROR("%d already holds heavyweight lock\n" , |
350 | context); |
351 | return false; |
352 | } |
353 | } while (atomic_cas_uint(lock, old, new) != old); |
354 | |
355 | return !_DRM_LOCK_IS_HELD(old); |
356 | } |
357 | |
358 | /* |
359 | * Release the lock held in the given context. Wake any waiters, |
360 | * preferring kernel waiters over userland waiters. |
361 | * |
362 | * Lock's spinlock must be held and lock must be held in this context. |
363 | */ |
364 | static void |
365 | drm_lock_release(struct drm_lock_data *lock_data, int context) |
366 | { |
367 | |
368 | (void)context; /* ignore */ |
369 | KASSERT(spin_is_locked(&lock_data->spinlock)); |
370 | KASSERT(_DRM_LOCK_IS_HELD(lock_data->hw_lock->lock)); |
371 | KASSERT(_DRM_LOCKING_CONTEXT(lock_data->hw_lock->lock) == context); |
372 | |
373 | lock_data->hw_lock->lock = 0; |
374 | DRM_SPIN_WAKEUP_ONE(&lock_data->lock_queue, &lock_data->spinlock); |
375 | } |
376 | |
377 | /* |
378 | * Block signals for a process that holds a drm lock. |
379 | * |
380 | * XXX It's not processes but files that hold drm locks, so blocking |
381 | * signals in a process seems wrong, and it's not clear that blocking |
382 | * signals automatically is remotely sensible anyway. |
383 | */ |
384 | static int |
385 | drm_lock_block_signals(struct drm_device *dev __unused, |
386 | struct drm_lock *lock_request __unused, struct drm_file *file __unused) |
387 | { |
388 | return 0; |
389 | } |
390 | |
391 | /* |
392 | * Unblock the signals that drm_lock_block_signals blocked. |
393 | */ |
394 | static void |
395 | drm_lock_unblock_signals(struct drm_device *dev __unused, |
396 | struct drm_lock *lock_request __unused, struct drm_file *file __unused) |
397 | { |
398 | } |
399 | |