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/*

 * Copyright (C) 2014 Red Hat

 * Author: Rob Clark 

 *

 * 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.

 */

#include 

#include 

#include 

/**

 * DOC: kms locking

 *

 * As KMS moves toward more fine grained locking, and atomic ioctl where

 * userspace can indirectly control locking order, it becomes necessary

 * to use ww_mutex and acquire-contexts to avoid deadlocks.  But because

 * the locking is more distributed around the driver code, we want a bit

 * of extra utility/tracking out of our acquire-ctx.  This is provided

 * by drm_modeset_lock / drm_modeset_acquire_ctx.

 *

 * For basic principles of ww_mutex, see: Documentation/ww-mutex-design.txt

 *

 * The basic usage pattern is to:

 *

 *     drm_modeset_acquire_init(&ctx)

 *   retry:

 *     foreach (lock in random_ordered_set_of_locks) {

 *       ret = drm_modeset_lock(lock, &ctx)

 *       if (ret == -EDEADLK) {

 *          drm_modeset_backoff(&ctx);

 *          goto retry;

 *       }

 *     }

 *

 *     ... do stuff ...

 *

 *     drm_modeset_drop_locks(&ctx);

 *     drm_modeset_acquire_fini(&ctx);

 */

/**

 * drm_modeset_acquire_init - initialize acquire context

 * @ctx: the acquire context

 * @flags: for future

 */

void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,

		uint32_t flags)

{

	memset(ctx, 0, sizeof(*ctx));

	ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);

	INIT_LIST_HEAD(&ctx->locked);

}

EXPORT_SYMBOL(drm_modeset_acquire_init);

/**

 * drm_modeset_acquire_fini - cleanup acquire context

 * @ctx: the acquire context

 */

void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)

{

	ww_acquire_fini(&ctx->ww_ctx);

}

EXPORT_SYMBOL(drm_modeset_acquire_fini);

/**

 * drm_modeset_drop_locks - drop all locks

 * @ctx: the acquire context

 *

 * Drop all locks currently held against this acquire context.

 */

void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)

{

	WARN_ON(ctx->contended);

	while (!list_empty(&ctx->locked)) {

		struct drm_modeset_lock *lock;

		lock = list_first_entry(&ctx->locked,

				struct drm_modeset_lock, head);

		drm_modeset_unlock(lock);

	}

}

EXPORT_SYMBOL(drm_modeset_drop_locks);

static inline int modeset_lock(struct drm_modeset_lock *lock,

		struct drm_modeset_acquire_ctx *ctx,

		bool interruptible, bool slow)

{

	int ret;

	WARN_ON(ctx->contended);

	if (interruptible && slow) {

		ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);

	} else if (interruptible) {

		ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);

	} else if (slow) {

		ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);

		ret = 0;

	} else {

		ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);

	}

	if (!ret) {

		WARN_ON(!list_empty(&lock->head));

		list_add(&lock->head, &ctx->locked);

	} else if (ret == -EALREADY) {

		/* we already hold the lock.. this is fine.  For atomic

		 * we will need to be able to drm_modeset_lock() things

		 * without having to keep track of what is already locked

		 * or not.

		 */

		ret = 0;

	} else if (ret == -EDEADLK) {

		ctx->contended = lock;

	}

	return ret;

}

static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,

		bool interruptible)

{

	struct drm_modeset_lock *contended = ctx->contended;

	ctx->contended = NULL;

	if (WARN_ON(!contended))

		return 0;

	drm_modeset_drop_locks(ctx);

	return modeset_lock(contended, ctx, interruptible, true);

}

/**

 * drm_modeset_backoff - deadlock avoidance backoff

 * @ctx: the acquire context

 *

 * If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),

 * you must call this function to drop all currently held locks and

 * block until the contended lock becomes available.

 */

void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)

{

	modeset_backoff(ctx, false);

}

EXPORT_SYMBOL(drm_modeset_backoff);

/**

 * drm_modeset_backoff_interruptible - deadlock avoidance backoff

 * @ctx: the acquire context

 *

 * Interruptible version of drm_modeset_backoff()

 */

int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)

{

	return modeset_backoff(ctx, true);

}

EXPORT_SYMBOL(drm_modeset_backoff_interruptible);

/**

 * drm_modeset_lock - take modeset lock

 * @lock: lock to take

 * @ctx: acquire ctx

 *

 * If ctx is not NULL, then its ww acquire context is used and the

 * lock will be tracked by the context and can be released by calling

 * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a

 * deadlock scenario has been detected and it is an error to attempt

 * to take any more locks without first calling drm_modeset_backoff().

 */

int drm_modeset_lock(struct drm_modeset_lock *lock,

		struct drm_modeset_acquire_ctx *ctx)

{

	if (ctx)

		return modeset_lock(lock, ctx, false, false);

	ww_mutex_lock(&lock->mutex, NULL);

	return 0;

}

EXPORT_SYMBOL(drm_modeset_lock);

/**

 * drm_modeset_lock_interruptible - take modeset lock

 * @lock: lock to take

 * @ctx: acquire ctx

 *

 * Interruptible version of drm_modeset_lock()

 */

int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,

		struct drm_modeset_acquire_ctx *ctx)

{

	if (ctx)

		return modeset_lock(lock, ctx, true, false);

	return ww_mutex_lock_interruptible(&lock->mutex, NULL);

}

EXPORT_SYMBOL(drm_modeset_lock_interruptible);

/**

 * drm_modeset_unlock - drop modeset lock

 * @lock: lock to release

 */

void drm_modeset_unlock(struct drm_modeset_lock *lock)

{

	list_del_init(&lock->head);

	ww_mutex_unlock(&lock->mutex);

}

EXPORT_SYMBOL(drm_modeset_unlock);

/* Temporary.. until we have sufficiently fine grained locking, there

 * are a couple scenarios where it is convenient to grab all crtc locks.

 * It is planned to remove this:

 */

int drm_modeset_lock_all_crtcs(struct drm_device *dev,

		struct drm_modeset_acquire_ctx *ctx)

{

	struct drm_mode_config *config = &dev->mode_config;

	struct drm_crtc *crtc;

	int ret = 0;

	list_for_each_entry(crtc, &config->crtc_list, head) {

		ret = drm_modeset_lock(&crtc->mutex, ctx);

		if (ret)

			return ret;

	}

	return 0;

}

EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);