ttm_lock.h

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 *
 * Copyright (c) 2007-2009 VMware, Inc., Palo Alto, CA., USA
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/*
 * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
 */

/** @file ttm_lock.h
 * This file implements a simple replacement for the buffer manager use
 * of the DRM heavyweight hardware lock.
 * The lock is a read-write lock. Taking it in read mode and write mode
 * is relatively fast, and intended for in-kernel use only.
 *
 * The vt mode is used only when there is a need to block all
 * user-space processes from validating buffers.
 * It's allowed to leave kernel space with the vt lock held.
 * If a user-space process dies while having the vt-lock,
 * it will be released during the file descriptor release. The vt lock
 * excludes write lock and read lock.
 *
 * The suspend mode is used to lock out all TTM users when preparing for
 * and executing suspend operations.
 *
 */

#ifndef _TTM_LOCK_H_
#define _TTM_LOCK_H_

#include <ttm/ttm_object.h>
#include <linux/wait.h>
#include <linux/atomic.h>

/**
 * struct ttm_lock
 *
 * @base: ttm base object used solely to release the lock if the client
 * holding the lock dies.
 * @queue: Queue for processes waiting for lock change-of-status.
 * @lock: Spinlock protecting some lock members.
 * @rw: Read-write lock counter. Protected by @lock.
 * @flags: Lock state. Protected by @lock.
 * @kill_takers: Boolean whether to kill takers of the lock.
 * @signal: Signal to send when kill_takers is true.
 */

struct ttm_lock {
	struct ttm_base_object base;
	wait_queue_head_t queue;
	spinlock_t lock;
	int32_t rw;
	uint32_t flags;
	bool kill_takers;
	int signal;
	struct ttm_object_file *vt_holder;
};


/**
 * ttm_lock_init
 *
 * @lock: Pointer to a struct ttm_lock
 * Initializes the lock.
 */
extern void ttm_lock_init(struct ttm_lock *lock);

/**
 * ttm_read_unlock
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Releases a read lock.
 */
extern void ttm_read_unlock(struct ttm_lock *lock);

/**
 * ttm_read_lock
 *
 * @lock: Pointer to a struct ttm_lock
 * @interruptible: Interruptible sleeping while waiting for a lock.
 *
 * Takes the lock in read mode.
 * Returns:
 * -ERESTARTSYS If interrupted by a signal and interruptible is true.
 */
extern int ttm_read_lock(struct ttm_lock *lock, bool interruptible);

/**
 * ttm_read_trylock
 *
 * @lock: Pointer to a struct ttm_lock
 * @interruptible: Interruptible sleeping while waiting for a lock.
 *
 * Tries to take the lock in read mode. If the lock is already held
 * in write mode, the function will return -EBUSY. If the lock is held
 * in vt or suspend mode, the function will sleep until these modes
 * are unlocked.
 *
 * Returns:
 * -EBUSY The lock was already held in write mode.
 * -ERESTARTSYS If interrupted by a signal and interruptible is true.
 */
extern int ttm_read_trylock(struct ttm_lock *lock, bool interruptible);

/**
 * ttm_write_unlock
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Releases a write lock.
 */
extern void ttm_write_unlock(struct ttm_lock *lock);

/**
 * ttm_write_lock
 *
 * @lock: Pointer to a struct ttm_lock
 * @interruptible: Interruptible sleeping while waiting for a lock.
 *
 * Takes the lock in write mode.
 * Returns:
 * -ERESTARTSYS If interrupted by a signal and interruptible is true.
 */
extern int ttm_write_lock(struct ttm_lock *lock, bool interruptible);

/**
 * ttm_lock_downgrade
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Downgrades a write lock to a read lock.
 */
extern void ttm_lock_downgrade(struct ttm_lock *lock);

/**
 * ttm_suspend_lock
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Takes the lock in suspend mode. Excludes read and write mode.
 */
extern void ttm_suspend_lock(struct ttm_lock *lock);

/**
 * ttm_suspend_unlock
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Releases a suspend lock
 */
extern void ttm_suspend_unlock(struct ttm_lock *lock);

/**
 * ttm_vt_lock
 *
 * @lock: Pointer to a struct ttm_lock
 * @interruptible: Interruptible sleeping while waiting for a lock.
 * @tfile: Pointer to a struct ttm_object_file to register the lock with.
 *
 * Takes the lock in vt mode.
 * Returns:
 * -ERESTARTSYS If interrupted by a signal and interruptible is true.
 * -ENOMEM: Out of memory when locking.
 */
extern int ttm_vt_lock(struct ttm_lock *lock, bool interruptible,
		       struct ttm_object_file *tfile);

/**
 * ttm_vt_unlock
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Releases a vt lock.
 * Returns:
 * -EINVAL If the lock was not held.
 */
extern int ttm_vt_unlock(struct ttm_lock *lock);

/**
 * ttm_write_unlock
 *
 * @lock: Pointer to a struct ttm_lock
 *
 * Releases a write lock.
 */
extern void ttm_write_unlock(struct ttm_lock *lock);

/**
 * ttm_write_lock
 *
 * @lock: Pointer to a struct ttm_lock
 * @interruptible: Interruptible sleeping while waiting for a lock.
 *
 * Takes the lock in write mode.
 * Returns:
 * -ERESTARTSYS If interrupted by a signal and interruptible is true.
 */
extern int ttm_write_lock(struct ttm_lock *lock, bool interruptible);

/**
 * ttm_lock_set_kill
 *
 * @lock: Pointer to a struct ttm_lock
 * @val: Boolean whether to kill processes taking the lock.
 * @signal: Signal to send to the process taking the lock.
 *
 * The kill-when-taking-lock functionality is used to kill processes that keep
 * on using the TTM functionality when its resources has been taken down, for
 * example when the X server exits. A typical sequence would look like this:
 * - X server takes lock in write mode.
 * - ttm_lock_set_kill() is called with @val set to true.
 * - As part of X server exit, TTM resources are taken down.
 * - X server releases the lock on file release.
 * - Another dri client wants to render, takes the lock and is killed.
 *
 */
static inline void ttm_lock_set_kill(struct ttm_lock *lock, bool val,
				     int signal)
{
	lock->kill_takers = val;
	if (val)
		lock->signal = signal;
}

#endif