1 // SPDX-License-Identifier: MIT 2 3 #ifdef __linux__ 4 #include <uapi/linux/sched/types.h> 5 #endif 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 48 void drm_handle_vblank_works(struct drm_vblank_crtc *vblank) 49 { 50 struct drm_vblank_work *work, *next; 51 u64 count = atomic64_read(&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(count, work->count)) 58 continue; 59 60 list_del_init(&work->node); 61 drm_vblank_put(vblank->dev, vblank->pipe); 62 kthread_queue_work(vblank->worker, &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 */ 72 void 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 list_for_each_entry_safe(work, next, &vblank->pending_work, node) { 79 list_del_init(&work->node); 80 drm_vblank_put(vblank->dev, vblank->pipe); 81 } 82 83 wake_up_all(&vblank->work_wait_queue); 84 } 85 86 /** 87 * drm_vblank_work_schedule - schedule a vblank work 88 * @work: vblank work to schedule 89 * @count: target vblank count 90 * @nextonmiss: defer until the next vblank if target vblank was missed 91 * 92 * Schedule @work for execution once the crtc vblank count reaches @count. 93 * 94 * If the crtc vblank count has already reached @count and @nextonmiss is 95 * %false the work starts to execute immediately. 96 * 97 * If the crtc vblank count has already reached @count and @nextonmiss is 98 * %true the work is deferred until the next vblank (as if @count has been 99 * specified as crtc vblank count + 1). 100 * 101 * If @work is already scheduled, this function will reschedule said work 102 * using the new @count. This can be used for self-rearming work items. 103 * 104 * Returns: 105 * %1 if @work was successfully (re)scheduled, %0 if it was either already 106 * scheduled or cancelled, or a negative error code on failure. 107 */ 108 int drm_vblank_work_schedule(struct drm_vblank_work *work, 109 u64 count, bool nextonmiss) 110 { 111 struct drm_vblank_crtc *vblank = work->vblank; 112 struct drm_device *dev = vblank->dev; 113 u64 cur_vbl; 114 unsigned long irqflags; 115 bool passed, inmodeset, rescheduling = false, wake = false; 116 int ret = 0; 117 118 spin_lock_irqsave(&dev->event_lock, irqflags); 119 if (work->cancelling) 120 goto out; 121 122 spin_lock(&dev->vbl_lock); 123 inmodeset = vblank->inmodeset; 124 spin_unlock(&dev->vbl_lock); 125 if (inmodeset) 126 goto out; 127 128 if (list_empty(&work->node)) { 129 ret = drm_vblank_get(dev, vblank->pipe); 130 if (ret < 0) 131 goto out; 132 } else if (work->count == count) { 133 /* Already scheduled w/ same vbl count */ 134 goto out; 135 } else { 136 rescheduling = true; 137 } 138 139 work->count = count; 140 cur_vbl = drm_vblank_count(dev, vblank->pipe); 141 passed = drm_vblank_passed(cur_vbl, count); 142 if (passed) 143 drm_dbg_core(dev, 144 "crtc %d vblank %llu already passed (current %llu)\n", 145 vblank->pipe, count, cur_vbl); 146 147 if (!nextonmiss && passed) { 148 drm_vblank_put(dev, vblank->pipe); 149 ret = kthread_queue_work(vblank->worker, &work->base); 150 151 if (rescheduling) { 152 list_del_init(&work->node); 153 wake = true; 154 } 155 } else { 156 if (!rescheduling) 157 list_add_tail(&work->node, &vblank->pending_work); 158 ret = true; 159 } 160 161 out: 162 spin_unlock_irqrestore(&dev->event_lock, irqflags); 163 if (wake) 164 wake_up_all(&vblank->work_wait_queue); 165 return ret; 166 } 167 EXPORT_SYMBOL(drm_vblank_work_schedule); 168 169 /** 170 * drm_vblank_work_cancel_sync - cancel a vblank work and wait for it to 171 * finish executing 172 * @work: vblank work to cancel 173 * 174 * Cancel an already scheduled vblank work and wait for its 175 * execution to finish. 176 * 177 * On return, @work is guaranteed to no longer be scheduled or running, even 178 * if it's self-arming. 179 * 180 * Returns: 181 * %True if the work was cancelled before it started to execute, %false 182 * otherwise. 183 */ 184 bool drm_vblank_work_cancel_sync(struct drm_vblank_work *work) 185 { 186 struct drm_vblank_crtc *vblank = work->vblank; 187 struct drm_device *dev = vblank->dev; 188 bool ret = false; 189 190 spin_lock_irq(&dev->event_lock); 191 if (!list_empty(&work->node)) { 192 list_del_init(&work->node); 193 drm_vblank_put(vblank->dev, vblank->pipe); 194 ret = true; 195 } 196 197 work->cancelling++; 198 spin_unlock_irq(&dev->event_lock); 199 200 wake_up_all(&vblank->work_wait_queue); 201 202 if (kthread_cancel_work_sync(&work->base)) 203 ret = true; 204 205 spin_lock_irq(&dev->event_lock); 206 work->cancelling--; 207 spin_unlock_irq(&dev->event_lock); 208 209 return ret; 210 } 211 EXPORT_SYMBOL(drm_vblank_work_cancel_sync); 212 213 /** 214 * drm_vblank_work_flush - wait for a scheduled vblank work to finish 215 * executing 216 * @work: vblank work to flush 217 * 218 * Wait until @work has finished executing once. 219 */ 220 void drm_vblank_work_flush(struct drm_vblank_work *work) 221 { 222 struct drm_vblank_crtc *vblank = work->vblank; 223 struct drm_device *dev = vblank->dev; 224 225 spin_lock_irq(&dev->event_lock); 226 wait_event_lock_irq(vblank->work_wait_queue, list_empty(&work->node), 227 dev->event_lock); 228 spin_unlock_irq(&dev->event_lock); 229 230 kthread_flush_work(&work->base); 231 } 232 EXPORT_SYMBOL(drm_vblank_work_flush); 233 234 /** 235 * drm_vblank_work_init - initialize a vblank work item 236 * @work: vblank work item 237 * @crtc: CRTC whose vblank will trigger the work execution 238 * @func: work function to be executed 239 * 240 * Initialize a vblank work item for a specific crtc. 241 */ 242 void drm_vblank_work_init(struct drm_vblank_work *work, struct drm_crtc *crtc, 243 void (*func)(struct kthread_work *work)) 244 { 245 kthread_init_work(&work->base, func); 246 INIT_LIST_HEAD(&work->node); 247 work->vblank = &crtc->dev->vblank[drm_crtc_index(crtc)]; 248 } 249 EXPORT_SYMBOL(drm_vblank_work_init); 250 251 int drm_vblank_worker_init(struct drm_vblank_crtc *vblank) 252 { 253 struct kthread_worker *worker; 254 255 INIT_LIST_HEAD(&vblank->pending_work); 256 init_waitqueue_head(&vblank->work_wait_queue); 257 worker = kthread_create_worker(0, "card%d-crtc%d", 258 vblank->dev->primary->index, 259 vblank->pipe); 260 if (IS_ERR(worker)) 261 return PTR_ERR(worker); 262 263 vblank->worker = worker; 264 265 #ifdef notyet 266 sched_set_fifo(worker->task); 267 #endif 268 return 0; 269 } 270