linux/drivers/gpu/drm/drm_vblank_work.c

// 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)
{ … }

/* 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)
{ … }

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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)
{ … }
EXPORT_SYMBOL(…);

/**
 * 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))
{ … }
EXPORT_SYMBOL(…);

int drm_vblank_worker_init(struct drm_vblank_crtc *vblank)
{ … }