1// SPDX-License-Identifier: GPL-2.0 OR MIT
2
3#include <drm/drm_exec.h>
4#include <drm/drm_gem.h>
5#include <linux/dma-resv.h>
6
7/**
8 * DOC: Overview
9 *
10 * This component mainly abstracts the retry loop necessary for locking
11 * multiple GEM objects while preparing hardware operations (e.g. command
12 * submissions, page table updates etc..).
13 *
14 * If a contention is detected while locking a GEM object the cleanup procedure
15 * unlocks all previously locked GEM objects and locks the contended one first
16 * before locking any further objects.
17 *
18 * After an object is locked fences slots can optionally be reserved on the
19 * dma_resv object inside the GEM object.
20 *
21 * A typical usage pattern should look like this::
22 *
23 * struct drm_gem_object *obj;
24 * struct drm_exec exec;
25 * unsigned long index;
26 * int ret;
27 *
28 * drm_exec_init(&exec, DRM_EXEC_INTERRUPTIBLE_WAIT);
29 * drm_exec_until_all_locked(&exec) {
30 * ret = drm_exec_prepare_obj(&exec, boA, 1);
31 * drm_exec_retry_on_contention(&exec);
32 * if (ret)
33 * goto error;
34 *
35 * ret = drm_exec_prepare_obj(&exec, boB, 1);
36 * drm_exec_retry_on_contention(&exec);
37 * if (ret)
38 * goto error;
39 * }
40 *
41 * drm_exec_for_each_locked_object(&exec, index, obj) {
42 * dma_resv_add_fence(obj->resv, fence, DMA_RESV_USAGE_READ);
43 * ...
44 * }
45 * drm_exec_fini(&exec);
46 *
47 * See struct dma_exec for more details.
48 */
49
50/* Dummy value used to initially enter the retry loop */
51#define DRM_EXEC_DUMMY ((void *)~0)
52
53/* Unlock all objects and drop references */
54static void drm_exec_unlock_all(struct drm_exec *exec)
55{
56 struct drm_gem_object *obj;
57 unsigned long index;
58
59 drm_exec_for_each_locked_object_reverse(exec, index, obj) {
60 dma_resv_unlock(obj: obj->resv);
61 drm_gem_object_put(obj);
62 }
63
64 drm_gem_object_put(obj: exec->prelocked);
65 exec->prelocked = NULL;
66}
67
68/**
69 * drm_exec_init - initialize a drm_exec object
70 * @exec: the drm_exec object to initialize
71 * @flags: controls locking behavior, see DRM_EXEC_* defines
72 * @nr: the initial # of objects
73 *
74 * Initialize the object and make sure that we can track locked objects.
75 *
76 * If nr is non-zero then it is used as the initial objects table size.
77 * In either case, the table will grow (be re-allocated) on demand.
78 */
79void drm_exec_init(struct drm_exec *exec, u32 flags, unsigned nr)
80{
81 if (!nr)
82 nr = PAGE_SIZE / sizeof(void *);
83
84 exec->flags = flags;
85 exec->objects = kvmalloc_array(n: nr, size: sizeof(void *), GFP_KERNEL);
86
87 /* If allocation here fails, just delay that till the first use */
88 exec->max_objects = exec->objects ? nr : 0;
89 exec->num_objects = 0;
90 exec->contended = DRM_EXEC_DUMMY;
91 exec->prelocked = NULL;
92}
93EXPORT_SYMBOL(drm_exec_init);
94
95/**
96 * drm_exec_fini - finalize a drm_exec object
97 * @exec: the drm_exec object to finalize
98 *
99 * Unlock all locked objects, drop the references to objects and free all memory
100 * used for tracking the state.
101 */
102void drm_exec_fini(struct drm_exec *exec)
103{
104 drm_exec_unlock_all(exec);
105 kvfree(addr: exec->objects);
106 if (exec->contended != DRM_EXEC_DUMMY) {
107 drm_gem_object_put(obj: exec->contended);
108 ww_acquire_fini(ctx: &exec->ticket);
109 }
110}
111EXPORT_SYMBOL(drm_exec_fini);
112
113/**
114 * drm_exec_cleanup - cleanup when contention is detected
115 * @exec: the drm_exec object to cleanup
116 *
117 * Cleanup the current state and return true if we should stay inside the retry
118 * loop, false if there wasn't any contention detected and we can keep the
119 * objects locked.
120 */
121bool drm_exec_cleanup(struct drm_exec *exec)
122{
123 if (likely(!exec->contended)) {
124 ww_acquire_done(ctx: &exec->ticket);
125 return false;
126 }
127
128 if (likely(exec->contended == DRM_EXEC_DUMMY)) {
129 exec->contended = NULL;
130 ww_acquire_init(ctx: &exec->ticket, ww_class: &reservation_ww_class);
131 return true;
132 }
133
134 drm_exec_unlock_all(exec);
135 exec->num_objects = 0;
136 return true;
137}
138EXPORT_SYMBOL(drm_exec_cleanup);
139
140/* Track the locked object in the array */
141static int drm_exec_obj_locked(struct drm_exec *exec,
142 struct drm_gem_object *obj)
143{
144 if (unlikely(exec->num_objects == exec->max_objects)) {
145 size_t size = exec->max_objects * sizeof(void *);
146 void *tmp;
147
148 tmp = kvrealloc(p: exec->objects, oldsize: size, newsize: size + PAGE_SIZE,
149 GFP_KERNEL);
150 if (!tmp)
151 return -ENOMEM;
152
153 exec->objects = tmp;
154 exec->max_objects += PAGE_SIZE / sizeof(void *);
155 }
156 drm_gem_object_get(obj);
157 exec->objects[exec->num_objects++] = obj;
158
159 return 0;
160}
161
162/* Make sure the contended object is locked first */
163static int drm_exec_lock_contended(struct drm_exec *exec)
164{
165 struct drm_gem_object *obj = exec->contended;
166 int ret;
167
168 if (likely(!obj))
169 return 0;
170
171 /* Always cleanup the contention so that error handling can kick in */
172 exec->contended = NULL;
173 if (exec->flags & DRM_EXEC_INTERRUPTIBLE_WAIT) {
174 ret = dma_resv_lock_slow_interruptible(obj: obj->resv,
175 ctx: &exec->ticket);
176 if (unlikely(ret))
177 goto error_dropref;
178 } else {
179 dma_resv_lock_slow(obj: obj->resv, ctx: &exec->ticket);
180 }
181
182 ret = drm_exec_obj_locked(exec, obj);
183 if (unlikely(ret))
184 goto error_unlock;
185
186 exec->prelocked = obj;
187 return 0;
188
189error_unlock:
190 dma_resv_unlock(obj: obj->resv);
191
192error_dropref:
193 drm_gem_object_put(obj);
194 return ret;
195}
196
197/**
198 * drm_exec_lock_obj - lock a GEM object for use
199 * @exec: the drm_exec object with the state
200 * @obj: the GEM object to lock
201 *
202 * Lock a GEM object for use and grab a reference to it.
203 *
204 * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
205 * already locked (can be suppressed by setting the DRM_EXEC_IGNORE_DUPLICATES
206 * flag), -ENOMEM when memory allocation failed and zero for success.
207 */
208int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
209{
210 int ret;
211
212 ret = drm_exec_lock_contended(exec);
213 if (unlikely(ret))
214 return ret;
215
216 if (exec->prelocked == obj) {
217 drm_gem_object_put(obj: exec->prelocked);
218 exec->prelocked = NULL;
219 return 0;
220 }
221
222 if (exec->flags & DRM_EXEC_INTERRUPTIBLE_WAIT)
223 ret = dma_resv_lock_interruptible(obj: obj->resv, ctx: &exec->ticket);
224 else
225 ret = dma_resv_lock(obj: obj->resv, ctx: &exec->ticket);
226
227 if (unlikely(ret == -EDEADLK)) {
228 drm_gem_object_get(obj);
229 exec->contended = obj;
230 return -EDEADLK;
231 }
232
233 if (unlikely(ret == -EALREADY) &&
234 exec->flags & DRM_EXEC_IGNORE_DUPLICATES)
235 return 0;
236
237 if (unlikely(ret))
238 return ret;
239
240 ret = drm_exec_obj_locked(exec, obj);
241 if (ret)
242 goto error_unlock;
243
244 return 0;
245
246error_unlock:
247 dma_resv_unlock(obj: obj->resv);
248 return ret;
249}
250EXPORT_SYMBOL(drm_exec_lock_obj);
251
252/**
253 * drm_exec_unlock_obj - unlock a GEM object in this exec context
254 * @exec: the drm_exec object with the state
255 * @obj: the GEM object to unlock
256 *
257 * Unlock the GEM object and remove it from the collection of locked objects.
258 * Should only be used to unlock the most recently locked objects. It's not time
259 * efficient to unlock objects locked long ago.
260 */
261void drm_exec_unlock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
262{
263 unsigned int i;
264
265 for (i = exec->num_objects; i--;) {
266 if (exec->objects[i] == obj) {
267 dma_resv_unlock(obj: obj->resv);
268 for (++i; i < exec->num_objects; ++i)
269 exec->objects[i - 1] = exec->objects[i];
270 --exec->num_objects;
271 drm_gem_object_put(obj);
272 return;
273 }
274
275 }
276}
277EXPORT_SYMBOL(drm_exec_unlock_obj);
278
279/**
280 * drm_exec_prepare_obj - prepare a GEM object for use
281 * @exec: the drm_exec object with the state
282 * @obj: the GEM object to prepare
283 * @num_fences: how many fences to reserve
284 *
285 * Prepare a GEM object for use by locking it and reserving fence slots.
286 *
287 * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
288 * already locked, -ENOMEM when memory allocation failed and zero for success.
289 */
290int drm_exec_prepare_obj(struct drm_exec *exec, struct drm_gem_object *obj,
291 unsigned int num_fences)
292{
293 int ret;
294
295 ret = drm_exec_lock_obj(exec, obj);
296 if (ret)
297 return ret;
298
299 ret = dma_resv_reserve_fences(obj: obj->resv, num_fences);
300 if (ret) {
301 drm_exec_unlock_obj(exec, obj);
302 return ret;
303 }
304
305 return 0;
306}
307EXPORT_SYMBOL(drm_exec_prepare_obj);
308
309/**
310 * drm_exec_prepare_array - helper to prepare an array of objects
311 * @exec: the drm_exec object with the state
312 * @objects: array of GEM object to prepare
313 * @num_objects: number of GEM objects in the array
314 * @num_fences: number of fences to reserve on each GEM object
315 *
316 * Prepares all GEM objects in an array, aborts on first error.
317 * Reserves @num_fences on each GEM object after locking it.
318 *
319 * Returns: -EDEADLOCK on contention, -EALREADY when object is already locked,
320 * -ENOMEM when memory allocation failed and zero for success.
321 */
322int drm_exec_prepare_array(struct drm_exec *exec,
323 struct drm_gem_object **objects,
324 unsigned int num_objects,
325 unsigned int num_fences)
326{
327 int ret;
328
329 for (unsigned int i = 0; i < num_objects; ++i) {
330 ret = drm_exec_prepare_obj(exec, objects[i], num_fences);
331 if (unlikely(ret))
332 return ret;
333 }
334
335 return 0;
336}
337EXPORT_SYMBOL(drm_exec_prepare_array);
338
339MODULE_DESCRIPTION("DRM execution context");
340MODULE_LICENSE("Dual MIT/GPL");
341

source code of linux/drivers/gpu/drm/drm_exec.c