1 files changed, 265 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_vblank_work.c b/drivers/gpu/drm/drm_vblank_work.c
new file mode 100644
index 000000000000..bd481fdd6b87
--- /dev/null
+++ b/drivers/gpu/drm/drm_vblank_work.c
@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: MIT
+
+#include <uapi/linux/sched/types.h>
+
+#include <drm/drm_print.h>
+#include <drm/drm_vblank.h>
+#include <drm/drm_vblank_work.h>
+#include <drm/drm_crtc.h>
+
+#include "drm_internal.h"
+
+/**
+ * DOC: vblank works
+ *
+ * Many DRM drivers need to program hardware in a time-sensitive manner, many
+ * times with a deadline of starting and finishing within a certain region of
+ * the scanout. Most of the time the safest way to accomplish this is to
+ * simply do said time-sensitive programming in the driver's IRQ handler,
+ * which allows drivers to avoid being preempted during these critical
+ * regions. Or even better, the hardware may even handle applying such
+ * time-critical programming independently of the CPU.
+ *
+ * While there's a decent amount of hardware that's designed so that the CPU
+ * doesn't need to be concerned with extremely time-sensitive programming,
+ * there's a few situations where it can't be helped. Some unforgiving
+ * hardware may require that certain time-sensitive programming be handled
+ * completely by the CPU, and said programming may even take too long to
+ * handle in an IRQ handler. Another such situation would be where the driver
+ * needs to perform a task that needs to complete within a specific scanout
+ * period, but might possibly block and thus cannot be handled in an IRQ
+ * context. Both of these situations can't be solved perfectly in Linux since
+ * we're not a realtime kernel, and thus the scheduler may cause us to miss
+ * our deadline if it decides to preempt us. But for some drivers, it's good
+ * enough if we can lower our chance of being preempted to an absolute
+ * minimum.
+ *
+ * This is where &drm_vblank_work comes in. &drm_vblank_work provides a simple
+ * generic delayed work implementation which delays work execution until a
+ * particular vblank has passed, and then executes the work at realtime
+ * priority. This provides the best possible chance at performing
+ * time-sensitive hardware programming on time, even when the system is under
+ * heavy load. &drm_vblank_work also supports rescheduling, so that self
+ * re-arming work items can be easily implemented.
+ */
+
+void drm_handle_vblank_works(struct drm_vblank_crtc *vblank)
+{
+	struct drm_vblank_work *work, *next;
+	u64 count = atomic64_read(&vblank->count);
+	bool wake = false;
+
+	assert_spin_locked(&vblank->dev->event_lock);
+
+	list_for_each_entry_safe(work, next, &vblank->pending_work, node) {
+		if (!drm_vblank_passed(count, work->count))
+			continue;
+
+		list_del_init(&work->node);
+		drm_vblank_put(vblank->dev, vblank->pipe);
+		kthread_queue_work(vblank->worker, &work->base);
+		wake = true;
+	}
+	if (wake)
+		wake_up_all(&vblank->work_wait_queue);
+}
+
+/* Handle cancelling any pending vblank work items and drop respective vblank
+ * references in response to vblank interrupts being disabled.
+ */
+void drm_vblank_cancel_pending_works(struct drm_vblank_crtc *vblank)
+{
+	struct drm_vblank_work *work, *next;
+
+	assert_spin_locked(&vblank->dev->event_lock);
+
+	list_for_each_entry_safe(work, next, &vblank->pending_work, node) {
+		list_del_init(&work->node);
+		drm_vblank_put(vblank->dev, vblank->pipe);
+	}
+
+	wake_up_all(&vblank->work_wait_queue);
+}
+
+/**
+ * drm_vblank_work_schedule - schedule a vblank work
+ * @work: vblank work to schedule
+ * @count: target vblank count
+ * @nextonmiss: defer until the next vblank if target vblank was missed
+ *
+ * Schedule @work for execution once the crtc vblank count reaches @count.
+ *
+ * If the crtc vblank count has already reached @count and @nextonmiss is
+ * %false the work starts to execute immediately.
+ *
+ * If the crtc vblank count has already reached @count and @nextonmiss is
+ * %true the work is deferred until the next vblank (as if @count has been
+ * specified as crtc vblank count + 1).
+ *
+ * If @work is already scheduled, this function will reschedule said work
+ * using the new @count. This can be used for self-rearming work items.
+ *
+ * Returns:
+ * %1 if @work was successfully (re)scheduled, %0 if it was either already
+ * scheduled or cancelled, or a negative error code on failure.
+ */
+int drm_vblank_work_schedule(struct drm_vblank_work *work,
+			     u64 count, bool nextonmiss)
+{
+	struct drm_vblank_crtc *vblank = work->vblank;
+	struct drm_device *dev = vblank->dev;
+	u64 cur_vbl;
+	unsigned long irqflags;
+	bool passed, inmodeset, rescheduling = false, wake = false;
+	int ret = 0;
+
+	spin_lock_irqsave(&dev->event_lock, irqflags);
+	if (work->cancelling)
+		goto out;
+
+	spin_lock(&dev->vbl_lock);
+	inmodeset = vblank->inmodeset;
+	spin_unlock(&dev->vbl_lock);
+	if (inmodeset)
+		goto out;
+
+	if (list_empty(&work->node)) {
+		ret = drm_vblank_get(dev, vblank->pipe);
+		if (ret < 0)
+			goto out;
+	} else if (work->count == count) {
+		/* Already scheduled w/ same vbl count */
+		goto out;
+	} else {
+		rescheduling = true;
+	}
+
+	work->count = count;
+	cur_vbl = drm_vblank_count(dev, vblank->pipe);
+	passed = drm_vblank_passed(cur_vbl, count);
+	if (passed)
+		drm_dbg_core(dev,
+			     "crtc %d vblank %llu already passed (current %llu)\n",
+			     vblank->pipe, count, cur_vbl);
+
+	if (!nextonmiss && passed) {
+		drm_vblank_put(dev, vblank->pipe);
+		ret = kthread_queue_work(vblank->worker, &work->base);
+
+		if (rescheduling) {
+			list_del_init(&work->node);
+			wake = true;
+		}
+	} else {
+		if (!rescheduling)
+			list_add_tail(&work->node, &vblank->pending_work);
+		ret = true;
+	}
+
+out:
+	spin_unlock_irqrestore(&dev->event_lock, irqflags);
+	if (wake)
+		wake_up_all(&vblank->work_wait_queue);
+	return ret;
+}
+EXPORT_SYMBOL(drm_vblank_work_schedule);
+
+/**
+ * drm_vblank_work_cancel_sync - cancel a vblank work and wait for it to
+ * finish executing
+ * @work: vblank work to cancel
+ *
+ * Cancel an already scheduled vblank work and wait for its
+ * execution to finish.
+ *
+ * On return, @work is guaranteed to no longer be scheduled or running, even
+ * if it's self-arming.
+ *
+ * Returns:
+ * %True if the work was cancelled before it started to execute, %false
+ * otherwise.
+ */
+bool drm_vblank_work_cancel_sync(struct drm_vblank_work *work)
+{
+	struct drm_vblank_crtc *vblank = work->vblank;
+	struct drm_device *dev = vblank->dev;
+	bool ret = false;
+
+	spin_lock_irq(&dev->event_lock);
+	if (!list_empty(&work->node)) {
+		list_del_init(&work->node);
+		drm_vblank_put(vblank->dev, vblank->pipe);
+		ret = true;
+	}
+
+	work->cancelling++;
+	spin_unlock_irq(&dev->event_lock);
+
+	wake_up_all(&vblank->work_wait_queue);
+
+	if (kthread_cancel_work_sync(&work->base))
+		ret = true;
+
+	spin_lock_irq(&dev->event_lock);
+	work->cancelling--;
+	spin_unlock_irq(&dev->event_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_vblank_work_cancel_sync);
+
+/**
+ * drm_vblank_work_flush - wait for a scheduled vblank work to finish
+ * executing
+ * @work: vblank work to flush
+ *
+ * Wait until @work has finished executing once.
+ */
+void drm_vblank_work_flush(struct drm_vblank_work *work)
+{
+	struct drm_vblank_crtc *vblank = work->vblank;
+	struct drm_device *dev = vblank->dev;
+
+	spin_lock_irq(&dev->event_lock);
+	wait_event_lock_irq(vblank->work_wait_queue, list_empty(&work->node),
+			    dev->event_lock);
+	spin_unlock_irq(&dev->event_lock);
+
+	kthread_flush_work(&work->base);
+}
+EXPORT_SYMBOL(drm_vblank_work_flush);
+
+/**
+ * drm_vblank_work_init - initialize a vblank work item
+ * @work: vblank work item
+ * @crtc: CRTC whose vblank will trigger the work execution
+ * @func: work function to be executed
+ *
+ * Initialize a vblank work item for a specific crtc.
+ */
+void drm_vblank_work_init(struct drm_vblank_work *work, struct drm_crtc *crtc,
+			  void (*func)(struct kthread_work *work))
+{
+	kthread_init_work(&work->base, func);
+	INIT_LIST_HEAD(&work->node);
+	work->vblank = &crtc->dev->vblank[drm_crtc_index(crtc)];
+}
+EXPORT_SYMBOL(drm_vblank_work_init);
+
+int drm_vblank_worker_init(struct drm_vblank_crtc *vblank)
+{
+	struct kthread_worker *worker;
+
+	INIT_LIST_HEAD(&vblank->pending_work);
+	init_waitqueue_head(&vblank->work_wait_queue);
+	worker = kthread_create_worker(0, "card%d-crtc%d",
+				       vblank->dev->primary->index,
+				       vblank->pipe);
+	if (IS_ERR(worker))
+		return PTR_ERR(worker);
+
+	vblank->worker = worker;
+
+	sched_set_fifo(worker->task);
+	return 0;
+}