1// SPDX-License-Identifier: MIT
2
3#include <uapi/linux/sched/types.h>
4
5#include <linux/export.h>
6
7#include <drm/drm_print.h>
8#include <drm/drm_vblank.h>
9#include <drm/drm_vblank_work.h>
10#include <drm/drm_crtc.h>
11
12#include "drm_internal.h"
13
14/**
15 * DOC: vblank works
16 *
17 * Many DRM drivers need to program hardware in a time-sensitive manner, many
18 * times with a deadline of starting and finishing within a certain region of
19 * the scanout. Most of the time the safest way to accomplish this is to
20 * simply do said time-sensitive programming in the driver's IRQ handler,
21 * which allows drivers to avoid being preempted during these critical
22 * regions. Or even better, the hardware may even handle applying such
23 * time-critical programming independently of the CPU.
24 *
25 * While there's a decent amount of hardware that's designed so that the CPU
26 * doesn't need to be concerned with extremely time-sensitive programming,
27 * there's a few situations where it can't be helped. Some unforgiving
28 * hardware may require that certain time-sensitive programming be handled
29 * completely by the CPU, and said programming may even take too long to
30 * handle in an IRQ handler. Another such situation would be where the driver
31 * needs to perform a task that needs to complete within a specific scanout
32 * period, but might possibly block and thus cannot be handled in an IRQ
33 * context. Both of these situations can't be solved perfectly in Linux since
34 * we're not a realtime kernel, and thus the scheduler may cause us to miss
35 * our deadline if it decides to preempt us. But for some drivers, it's good
36 * enough if we can lower our chance of being preempted to an absolute
37 * minimum.
38 *
39 * This is where &drm_vblank_work comes in. &drm_vblank_work provides a simple
40 * generic delayed work implementation which delays work execution until a
41 * particular vblank has passed, and then executes the work at realtime
42 * priority. This provides the best possible chance at performing
43 * time-sensitive hardware programming on time, even when the system is under
44 * heavy load. &drm_vblank_work also supports rescheduling, so that self
45 * re-arming work items can be easily implemented.
46 */
47
48void drm_handle_vblank_works(struct drm_vblank_crtc *vblank)
49{
50 struct drm_vblank_work *work, *next;
51 u64 count = atomic64_read(v: &vblank->count);
52 bool wake = false;
53
54 assert_spin_locked(&vblank->dev->event_lock);
55
56 list_for_each_entry_safe(work, next, &vblank->pending_work, node) {
57 if (!drm_vblank_passed(seq: count, ref: work->count))
58 continue;
59
60 list_del_init(entry: &work->node);
61 drm_vblank_put(dev: vblank->dev, pipe: vblank->pipe);
62 kthread_queue_work(worker: vblank->worker, work: &work->base);
63 wake = true;
64 }
65 if (wake)
66 wake_up_all(&vblank->work_wait_queue);
67}
68
69/* Handle cancelling any pending vblank work items and drop respective vblank
70 * references in response to vblank interrupts being disabled.
71 */
72void drm_vblank_cancel_pending_works(struct drm_vblank_crtc *vblank)
73{
74 struct drm_vblank_work *work, *next;
75
76 assert_spin_locked(&vblank->dev->event_lock);
77
78 drm_WARN_ONCE(vblank->dev, !list_empty(&vblank->pending_work),
79 "Cancelling pending vblank works!\n");
80
81 list_for_each_entry_safe(work, next, &vblank->pending_work, node) {
82 list_del_init(entry: &work->node);
83 drm_vblank_put(dev: vblank->dev, pipe: vblank->pipe);
84 }
85
86 wake_up_all(&vblank->work_wait_queue);
87}
88
89/**
90 * drm_vblank_work_schedule - schedule a vblank work
91 * @work: vblank work to schedule
92 * @count: target vblank count
93 * @nextonmiss: defer until the next vblank if target vblank was missed
94 *
95 * Schedule @work for execution once the crtc vblank count reaches @count.
96 *
97 * If the crtc vblank count has already reached @count and @nextonmiss is
98 * %false the work starts to execute immediately.
99 *
100 * If the crtc vblank count has already reached @count and @nextonmiss is
101 * %true the work is deferred until the next vblank (as if @count has been
102 * specified as crtc vblank count + 1).
103 *
104 * If @work is already scheduled, this function will reschedule said work
105 * using the new @count. This can be used for self-rearming work items.
106 *
107 * Returns:
108 * %1 if @work was successfully (re)scheduled, %0 if it was either already
109 * scheduled or cancelled, or a negative error code on failure.
110 */
111int drm_vblank_work_schedule(struct drm_vblank_work *work,
112 u64 count, bool nextonmiss)
113{
114 struct drm_vblank_crtc *vblank = work->vblank;
115 struct drm_device *dev = vblank->dev;
116 u64 cur_vbl;
117 unsigned long irqflags;
118 bool passed, inmodeset, rescheduling = false, wake = false;
119 int ret = 0;
120
121 spin_lock_irqsave(&dev->event_lock, irqflags);
122 if (work->cancelling)
123 goto out;
124
125 spin_lock(lock: &dev->vbl_lock);
126 inmodeset = vblank->inmodeset;
127 spin_unlock(lock: &dev->vbl_lock);
128 if (inmodeset)
129 goto out;
130
131 if (list_empty(head: &work->node)) {
132 ret = drm_vblank_get(dev, pipe: vblank->pipe);
133 if (ret < 0)
134 goto out;
135 } else if (work->count == count) {
136 /* Already scheduled w/ same vbl count */
137 goto out;
138 } else {
139 rescheduling = true;
140 }
141
142 work->count = count;
143 cur_vbl = drm_vblank_count(dev, pipe: vblank->pipe);
144 passed = drm_vblank_passed(seq: cur_vbl, ref: count);
145 if (passed)
146 drm_dbg_core(dev,
147 "crtc %d vblank %llu already passed (current %llu)\n",
148 vblank->pipe, count, cur_vbl);
149
150 if (!nextonmiss && passed) {
151 drm_vblank_put(dev, pipe: vblank->pipe);
152 ret = kthread_queue_work(worker: vblank->worker, work: &work->base);
153
154 if (rescheduling) {
155 list_del_init(entry: &work->node);
156 wake = true;
157 }
158 } else {
159 if (!rescheduling)
160 list_add_tail(new: &work->node, head: &vblank->pending_work);
161 ret = true;
162 }
163
164out:
165 spin_unlock_irqrestore(lock: &dev->event_lock, flags: irqflags);
166 if (wake)
167 wake_up_all(&vblank->work_wait_queue);
168 return ret;
169}
170EXPORT_SYMBOL(drm_vblank_work_schedule);
171
172/**
173 * drm_vblank_work_cancel_sync - cancel a vblank work and wait for it to
174 * finish executing
175 * @work: vblank work to cancel
176 *
177 * Cancel an already scheduled vblank work and wait for its
178 * execution to finish.
179 *
180 * On return, @work is guaranteed to no longer be scheduled or running, even
181 * if it's self-arming.
182 *
183 * Returns:
184 * %True if the work was cancelled before it started to execute, %false
185 * otherwise.
186 */
187bool drm_vblank_work_cancel_sync(struct drm_vblank_work *work)
188{
189 struct drm_vblank_crtc *vblank = work->vblank;
190 struct drm_device *dev = vblank->dev;
191 bool ret = false;
192
193 spin_lock_irq(lock: &dev->event_lock);
194 if (!list_empty(head: &work->node)) {
195 list_del_init(entry: &work->node);
196 drm_vblank_put(dev: vblank->dev, pipe: vblank->pipe);
197 ret = true;
198 }
199
200 work->cancelling++;
201 spin_unlock_irq(lock: &dev->event_lock);
202
203 wake_up_all(&vblank->work_wait_queue);
204
205 if (kthread_cancel_work_sync(work: &work->base))
206 ret = true;
207
208 spin_lock_irq(lock: &dev->event_lock);
209 work->cancelling--;
210 spin_unlock_irq(lock: &dev->event_lock);
211
212 return ret;
213}
214EXPORT_SYMBOL(drm_vblank_work_cancel_sync);
215
216/**
217 * drm_vblank_work_flush - wait for a scheduled vblank work to finish
218 * executing
219 * @work: vblank work to flush
220 *
221 * Wait until @work has finished executing once.
222 */
223void drm_vblank_work_flush(struct drm_vblank_work *work)
224{
225 struct drm_vblank_crtc *vblank = work->vblank;
226 struct drm_device *dev = vblank->dev;
227
228 spin_lock_irq(lock: &dev->event_lock);
229 wait_event_lock_irq(vblank->work_wait_queue, list_empty(&work->node),
230 dev->event_lock);
231 spin_unlock_irq(lock: &dev->event_lock);
232
233 kthread_flush_work(work: &work->base);
234}
235EXPORT_SYMBOL(drm_vblank_work_flush);
236
237/**
238 * drm_vblank_work_flush_all - flush all currently pending vblank work on crtc.
239 * @crtc: crtc for which vblank work to flush
240 *
241 * Wait until all currently queued vblank work on @crtc
242 * has finished executing once.
243 */
244void drm_vblank_work_flush_all(struct drm_crtc *crtc)
245{
246 struct drm_device *dev = crtc->dev;
247 struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
248
249 spin_lock_irq(lock: &dev->event_lock);
250 wait_event_lock_irq(vblank->work_wait_queue,
251 list_empty(&vblank->pending_work),
252 dev->event_lock);
253 spin_unlock_irq(lock: &dev->event_lock);
254
255 kthread_flush_worker(worker: vblank->worker);
256}
257EXPORT_SYMBOL(drm_vblank_work_flush_all);
258
259/**
260 * drm_vblank_work_init - initialize a vblank work item
261 * @work: vblank work item
262 * @crtc: CRTC whose vblank will trigger the work execution
263 * @func: work function to be executed
264 *
265 * Initialize a vblank work item for a specific crtc.
266 */
267void drm_vblank_work_init(struct drm_vblank_work *work, struct drm_crtc *crtc,
268 void (*func)(struct kthread_work *work))
269{
270 kthread_init_work(&work->base, func);
271 INIT_LIST_HEAD(list: &work->node);
272 work->vblank = drm_crtc_vblank_crtc(crtc);
273}
274EXPORT_SYMBOL(drm_vblank_work_init);
275
276int drm_vblank_worker_init(struct drm_vblank_crtc *vblank)
277{
278 struct kthread_worker *worker;
279
280 INIT_LIST_HEAD(list: &vblank->pending_work);
281 init_waitqueue_head(&vblank->work_wait_queue);
282 worker = kthread_run_worker(0, "card%d-crtc%d",
283 vblank->dev->primary->index,
284 vblank->pipe);
285 if (IS_ERR(ptr: worker))
286 return PTR_ERR(ptr: worker);
287
288 vblank->worker = worker;
289
290 sched_set_fifo(p: worker->task);
291 return 0;
292}
293

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