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