drm_modeset_lock.h

/*
 * Copyright (C) 2014 Red Hat
 * Author: Rob Clark <robdclark@gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef DRM_MODESET_LOCK_H_
#define DRM_MODESET_LOCK_H_

#include <linux/types.h> /* stackdepot.h is not self-contained */
#include <linux/stackdepot.h>
#include <linux/ww_mutex.h>

struct drm_modeset_lock;

/**
 * struct drm_modeset_acquire_ctx - locking context (see ww_acquire_ctx)
 * @ww_ctx: base acquire ctx
 * @contended: used internally for -EDEADLK handling
 * @stack_depot: used internally for contention debugging
 * @locked: list of held locks
 * @trylock_only: trylock mode used in atomic contexts/panic notifiers
 * @interruptible: whether interruptible locking should be used.
 *
 * Each thread competing for a set of locks must use one acquire
 * ctx.  And if any lock fxn returns -EDEADLK, it must backoff and
 * retry.
 */
struct drm_modeset_acquire_ctx {

	struct ww_acquire_ctx ww_ctx;

	/*
	 * Contended lock: if a lock is contended you should only call
	 * drm_modeset_backoff() which drops locks and slow-locks the
	 * contended lock.
	 */
	struct drm_modeset_lock *contended;

	/*
	 * Stack depot for debugging when a contended lock was not backed off
	 * from.
	 */
	depot_stack_handle_t stack_depot;

	/*
	 * list of held locks (drm_modeset_lock)
	 */
	struct list_head locked;

	/*
	 * Trylock mode, use only for panic handlers!
	 */
	bool trylock_only;

	/* Perform interruptible waits on this context. */
	bool interruptible;
};

/**
 * struct drm_modeset_lock - used for locking modeset resources.
 * @mutex: resource locking
 * @head: used to hold its place on &drm_atomi_state.locked list when
 *    part of an atomic update
 *
 * Used for locking CRTCs and other modeset resources.
 */
struct drm_modeset_lock {
	/*
	 * modeset lock
	 */
	struct ww_mutex mutex;

	/*
	 * Resources that are locked as part of an atomic update are added
	 * to a list (so we know what to unlock at the end).
	 */
	struct list_head head;
};

#define DRM_MODESET_ACQUIRE_INTERRUPTIBLE BIT(0)

void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
		uint32_t flags);
void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx);
void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx);
int drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx);

void drm_modeset_lock_init(struct drm_modeset_lock *lock);

/**
 * drm_modeset_lock_fini - cleanup lock
 * @lock: lock to cleanup
 */
static inline void drm_modeset_lock_fini(struct drm_modeset_lock *lock)
{
	WARN_ON(!list_empty(&lock->head));
}

/**
 * drm_modeset_is_locked - equivalent to mutex_is_locked()
 * @lock: lock to check
 */
static inline bool drm_modeset_is_locked(struct drm_modeset_lock *lock)
{
	return ww_mutex_is_locked(&lock->mutex);
}

/**
 * drm_modeset_lock_assert_held - equivalent to lockdep_assert_held()
 * @lock: lock to check
 */
static inline void drm_modeset_lock_assert_held(struct drm_modeset_lock *lock)
{
	lockdep_assert_held(&lock->mutex.base);
}

int drm_modeset_lock(struct drm_modeset_lock *lock,
		struct drm_modeset_acquire_ctx *ctx);
int __must_check drm_modeset_lock_single_interruptible(struct drm_modeset_lock *lock);
void drm_modeset_unlock(struct drm_modeset_lock *lock);

struct drm_device;
struct drm_crtc;
struct drm_plane;

void drm_modeset_lock_all(struct drm_device *dev);
void drm_modeset_unlock_all(struct drm_device *dev);
void drm_warn_on_modeset_not_all_locked(struct drm_device *dev);

int drm_modeset_lock_all_ctx(struct drm_device *dev,
			     struct drm_modeset_acquire_ctx *ctx);

/**
 * DRM_MODESET_LOCK_ALL_BEGIN - Helper to acquire modeset locks
 * @dev: drm device
 * @ctx: local modeset acquire context, will be dereferenced
 * @flags: DRM_MODESET_ACQUIRE_* flags to pass to drm_modeset_acquire_init()
 * @ret: local ret/err/etc variable to track error status
 *
 * Use these macros to simplify grabbing all modeset locks using a local
 * context. This has the advantage of reducing boilerplate, but also properly
 * checking return values where appropriate.
 *
 * Any code run between BEGIN and END will be holding the modeset locks.
 *
 * This must be paired with DRM_MODESET_LOCK_ALL_END(). We will jump back and
 * forth between the labels on deadlock and error conditions.
 *
 * Drivers can acquire additional modeset locks. If any lock acquisition
 * fails, the control flow needs to jump to DRM_MODESET_LOCK_ALL_END() with
 * the @ret parameter containing the return value of drm_modeset_lock().
 *
 * Returns:
 * The only possible value of ret immediately after DRM_MODESET_LOCK_ALL_BEGIN()
 * is 0, so no error checking is necessary
 */
#define DRM_MODESET_LOCK_ALL_BEGIN(dev, ctx, flags, ret)		\
	if (!drm_drv_uses_atomic_modeset(dev))				\
		mutex_lock(&dev->mode_config.mutex);			\
	drm_modeset_acquire_init(&ctx, flags);				\
modeset_lock_retry:							\
	ret = drm_modeset_lock_all_ctx(dev, &ctx);			\
	if (ret)							\
		goto modeset_lock_fail;

/**
 * DRM_MODESET_LOCK_ALL_END - Helper to release and cleanup modeset locks
 * @dev: drm device
 * @ctx: local modeset acquire context, will be dereferenced
 * @ret: local ret/err/etc variable to track error status
 *
 * The other side of DRM_MODESET_LOCK_ALL_BEGIN(). It will bounce back to BEGIN
 * if ret is -EDEADLK.
 *
 * It's important that you use the same ret variable for begin and end so
 * deadlock conditions are properly handled.
 *
 * Returns:
 * ret will be untouched unless it is -EDEADLK on entry. That means that if you
 * successfully acquire the locks, ret will be whatever your code sets it to. If
 * there is a deadlock or other failure with acquire or backoff, ret will be set
 * to that failure. In both of these cases the code between BEGIN/END will not
 * be run, so the failure will reflect the inability to grab the locks.
 */
#define DRM_MODESET_LOCK_ALL_END(dev, ctx, ret)				\
modeset_lock_fail:							\
	if (ret == -EDEADLK) {						\
		ret = drm_modeset_backoff(&ctx);			\
		if (!ret)						\
			goto modeset_lock_retry;			\
	}								\
	drm_modeset_drop_locks(&ctx);					\
	drm_modeset_acquire_fini(&ctx);					\
	if (!drm_drv_uses_atomic_modeset(dev))				\
		mutex_unlock(&dev->mode_config.mutex);

#endif /* DRM_MODESET_LOCK_H_ */