// 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);
drm_WARN_ONCE(vblank->dev, !list_empty(&vblank->pending_work),
"Cancelling pending vblank works!\n");
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_flush_all - flush all currently pending vblank work on crtc.
* @crtc: crtc for which vblank work to flush
*
* Wait until all currently queued vblank work on @crtc
* has finished executing once.
*/
void drm_vblank_work_flush_all(struct drm_crtc *crtc)
{
struct drm_device *dev = crtc->dev;
struct drm_vblank_crtc *vblank = &dev->vblank[drm_crtc_index(crtc)];
spin_lock_irq(&dev->event_lock);
wait_event_lock_irq(vblank->work_wait_queue,
list_empty(&vblank->pending_work),
dev->event_lock);
spin_unlock_irq(&dev->event_lock);
kthread_flush_worker(vblank->worker);
}
EXPORT_SYMBOL(drm_vblank_work_flush_all);
/**
* 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 = drm_crtc_vblank_crtc(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;
}
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