/**
 * \file drm_lock.c
 * IOCTLs for locking
 *
 * \author Rickard E. (Rik) Faith <faith@valinux.com>
 * \author Gareth Hughes <gareth@valinux.com>
 */

/*
 * Created: Tue Feb  2 08:37:54 1999 by faith@valinux.com
 *
 * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
 * Copyright 2000 VA Linux Systems, Inc., Sunnyvale, California.
 * All Rights Reserved.
 *
 * 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 (including the next
 * paragraph) 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
 * VA LINUX SYSTEMS AND/OR ITS SUPPLIERS 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 <linux/export.h>
#include <linux/sched/signal.h>

#include <drm/drmP.h>
#include "drm_legacy.h"
#include "drm_internal.h"

static int drm_lock_take(struct drm_lock_data *lock_data, unsigned int context);

/**
 * Take the heavyweight lock.
 *
 * \param lock lock pointer.
 * \param context locking context.
 * \return one if the lock is held, or zero otherwise.
 *
 * Attempt to mark the lock as held by the given context, via the \p cmpxchg instruction.
 */
static
int drm_lock_take(struct drm_lock_data *lock_data,
                  unsigned int context)
{
        unsigned int old, new, prev;
        volatile unsigned int *lock = &lock_data->hw_lock->lock;

        spin_lock_bh(&lock_data->spinlock);
        do {
                old = *lock;
                if (old & _DRM_LOCK_HELD)
                        new = old | _DRM_LOCK_CONT;
                else {
                        new = context | _DRM_LOCK_HELD |
                                ((lock_data->user_waiters + lock_data->kernel_waiters > 1) ?
                                 _DRM_LOCK_CONT : 0);
                }
                prev = cmpxchg(lock, old, new);
        } while (prev != old);
        spin_unlock_bh(&lock_data->spinlock);

        if (_DRM_LOCKING_CONTEXT(old) == context) {
                if (old & _DRM_LOCK_HELD) {
                        if (context != DRM_KERNEL_CONTEXT) {
                                DRM_ERROR("%d holds heavyweight lock\n",
                                          context);
                        }
                        return 0;
                }
        }

        if ((_DRM_LOCKING_CONTEXT(new)) == context && (new & _DRM_LOCK_HELD)) {
                /* Have lock */
                return 1;
        }
        return 0;
}

/**
 * This takes a lock forcibly and hands it to context.  Should ONLY be used
 * inside *_unlock to give lock to kernel before calling *_dma_schedule.
 *
 * \param dev DRM device.
 * \param lock lock pointer.
 * \param context locking context.
 * \return always one.
 *
 * Resets the lock file pointer.
 * Marks the lock as held by the given context, via the \p cmpxchg instruction.
 */
static int drm_lock_transfer(struct drm_lock_data *lock_data,
                             unsigned int context)
{
        unsigned int old, new, prev;
        volatile unsigned int *lock = &lock_data->hw_lock->lock;

        lock_data->file_priv = NULL;
        do {
                old = *lock;
                new = context | _DRM_LOCK_HELD;
                prev = cmpxchg(lock, old, new);
        } while (prev != old);
        return 1;
}

static int drm_legacy_lock_free(struct drm_lock_data *lock_data,
                                unsigned int context)
{
        unsigned int old, new, prev;
        volatile unsigned int *lock = &lock_data->hw_lock->lock;

        spin_lock_bh(&lock_data->spinlock);
        if (lock_data->kernel_waiters != 0) {
                drm_lock_transfer(lock_data, 0);
                lock_data->idle_has_lock = 1;
                spin_unlock_bh(&lock_data->spinlock);
                return 1;
        }
        spin_unlock_bh(&lock_data->spinlock);

        do {
                old = *lock;
                new = _DRM_LOCKING_CONTEXT(old);
                prev = cmpxchg(lock, old, new);
        } while (prev != old);

        if (_DRM_LOCK_IS_HELD(old) && _DRM_LOCKING_CONTEXT(old) != context) {
                DRM_ERROR("%d freed heavyweight lock held by %d\n",
                          context, _DRM_LOCKING_CONTEXT(old));
                return 1;
        }
        wake_up_interruptible(&lock_data->lock_queue);
        return 0;
}

/**
 * Lock ioctl.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param arg user argument, pointing to a drm_lock structure.
 * \return zero on success or negative number on failure.
 *
 * Add the current task to the lock wait queue, and attempt to take to lock.
 */
int drm_legacy_lock(struct drm_device *dev, void *data,
                    struct drm_file *file_priv)
{
        DECLARE_WAITQUEUE(entry, current);
        struct drm_lock *lock = data;
        struct drm_master *master = file_priv->master;
        int ret = 0;

        if (!drm_core_check_feature(dev, DRIVER_LEGACY))
                return -EOPNOTSUPP;

        ++file_priv->lock_count;

        if (lock->context == DRM_KERNEL_CONTEXT) {
                DRM_ERROR("Process %d using kernel context %d\n",
                          task_pid_nr(current), lock->context);
                return -EINVAL;
        }

        DRM_DEBUG("%d (pid %d) requests lock (0x%08x), flags = 0x%08x\n",
                  lock->context, task_pid_nr(current),
                  master->lock.hw_lock ? master->lock.hw_lock->lock : -1,
                  lock->flags);

        add_wait_queue(&master->lock.lock_queue, &entry);
        spin_lock_bh(&master->lock.spinlock);
        master->lock.user_waiters++;
        spin_unlock_bh(&master->lock.spinlock);

        for (;;) {
                __set_current_state(TASK_INTERRUPTIBLE);
                if (!master->lock.hw_lock) {
                        /* Device has been unregistered */
                        send_sig(SIGTERM, current, 0);
                        ret = -EINTR;
                        break;
                }
                if (drm_lock_take(&master->lock, lock->context)) {
                        master->lock.file_priv = file_priv;
                        master->lock.lock_time = jiffies;
                        break;  /* Got lock */
                }

                /* Contention */
                mutex_unlock(&drm_global_mutex);
                schedule();
                mutex_lock(&drm_global_mutex);
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }
        }
        spin_lock_bh(&master->lock.spinlock);
        master->lock.user_waiters--;
        spin_unlock_bh(&master->lock.spinlock);
        __set_current_state(TASK_RUNNING);
        remove_wait_queue(&master->lock.lock_queue, &entry);

        DRM_DEBUG("%d %s\n", lock->context,
                  ret ? "interrupted" : "has lock");
        if (ret) return ret;

        /* don't set the block all signals on the master process for now 
         * really probably not the correct answer but lets us debug xkb
         * xserver for now */
        if (!drm_is_current_master(file_priv)) {
                dev->sigdata.context = lock->context;
                dev->sigdata.lock = master->lock.hw_lock;
        }

        if (dev->driver->dma_quiescent && (lock->flags & _DRM_LOCK_QUIESCENT))
        {
                if (dev->driver->dma_quiescent(dev)) {
                        DRM_DEBUG("%d waiting for DMA quiescent\n",
                                  lock->context);
                        return -EBUSY;
                }
        }

        return 0;
}

/**
 * Unlock ioctl.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param arg user argument, pointing to a drm_lock structure.
 * \return zero on success or negative number on failure.
 *
 * Transfer and free the lock.
 */
int drm_legacy_unlock(struct drm_device *dev, void *data, struct drm_file *file_priv)
{
        struct drm_lock *lock = data;
        struct drm_master *master = file_priv->master;

        if (!drm_core_check_feature(dev, DRIVER_LEGACY))
                return -EOPNOTSUPP;

        if (lock->context == DRM_KERNEL_CONTEXT) {
                DRM_ERROR("Process %d using kernel context %d\n",
                          task_pid_nr(current), lock->context);
                return -EINVAL;
        }

        if (drm_legacy_lock_free(&master->lock, lock->context)) {
                /* FIXME: Should really bail out here. */
        }

        return 0;
}

/**
 * This function returns immediately and takes the hw lock
 * with the kernel context if it is free, otherwise it gets the highest priority when and if
 * it is eventually released.
 *
 * This guarantees that the kernel will _eventually_ have the lock _unless_ it is held
 * by a blocked process. (In the latter case an explicit wait for the hardware lock would cause
 * a deadlock, which is why the "idlelock" was invented).
 *
 * This should be sufficient to wait for GPU idle without
 * having to worry about starvation.
 */

void drm_legacy_idlelock_take(struct drm_lock_data *lock_data)
{
        int ret;

        spin_lock_bh(&lock_data->spinlock);
        lock_data->kernel_waiters++;
        if (!lock_data->idle_has_lock) {

                spin_unlock_bh(&lock_data->spinlock);
                ret = drm_lock_take(lock_data, DRM_KERNEL_CONTEXT);
                spin_lock_bh(&lock_data->spinlock);

                if (ret == 1)
                        lock_data->idle_has_lock = 1;
        }
        spin_unlock_bh(&lock_data->spinlock);
}
EXPORT_SYMBOL(drm_legacy_idlelock_take);

void drm_legacy_idlelock_release(struct drm_lock_data *lock_data)
{
        unsigned int old, prev;
        volatile unsigned int *lock = &lock_data->hw_lock->lock;

        spin_lock_bh(&lock_data->spinlock);
        if (--lock_data->kernel_waiters == 0) {
                if (lock_data->idle_has_lock) {
                        do {
                                old = *lock;
                                prev = cmpxchg(lock, old, DRM_KERNEL_CONTEXT);
                        } while (prev != old);
                        wake_up_interruptible(&lock_data->lock_queue);
                        lock_data->idle_has_lock = 0;
                }
        }
        spin_unlock_bh(&lock_data->spinlock);
}
EXPORT_SYMBOL(drm_legacy_idlelock_release);

static int drm_legacy_i_have_hw_lock(struct drm_device *dev,
                                     struct drm_file *file_priv)
{
        struct drm_master *master = file_priv->master;
        return (file_priv->lock_count && master->lock.hw_lock &&
                _DRM_LOCK_IS_HELD(master->lock.hw_lock->lock) &&
                master->lock.file_priv == file_priv);
}

void drm_legacy_lock_release(struct drm_device *dev, struct file *filp)
{
        struct drm_file *file_priv = filp->private_data;

        /* if the master has gone away we can't do anything with the lock */
        if (!dev->master)
                return;

        if (drm_legacy_i_have_hw_lock(dev, file_priv)) {
                DRM_DEBUG("File %p released, freeing lock for context %d\n",
                          filp, _DRM_LOCKING_CONTEXT(file_priv->master->lock.hw_lock->lock));
                drm_legacy_lock_free(&file_priv->master->lock,
                                     _DRM_LOCKING_CONTEXT(file_priv->master->lock.hw_lock->lock));
        }
}