Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6

[deliverable/linux.git] / drivers / gpu / drm / drm_irq.c

/**
 * \file drm_irq.c
 * IRQ support
 *
 * \author Rickard E. (Rik) Faith <faith@valinux.com>
 * \author Gareth Hughes <gareth@valinux.com>
 */

/*
 * Created: Fri Mar 19 14:30:16 1999 by faith@valinux.com
 *
 * Copyright 1999, 2000 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 "drmP.h"

#include <linux/interrupt.h>    /* For task queue support */

/**
 * Get interrupt from bus id.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param arg user argument, pointing to a drm_irq_busid structure.
 * \return zero on success or a negative number on failure.
 *
 * Finds the PCI device with the specified bus id and gets its IRQ number.
 * This IOCTL is deprecated, and will now return EINVAL for any busid not equal
 * to that of the device that this DRM instance attached to.
 */
int drm_irq_by_busid(struct drm_device *dev, void *data,
                     struct drm_file *file_priv)
{
        struct drm_irq_busid *p = data;

        if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
                return -EINVAL;

        if ((p->busnum >> 8) != drm_get_pci_domain(dev) ||
            (p->busnum & 0xff) != dev->pdev->bus->number ||
            p->devnum != PCI_SLOT(dev->pdev->devfn) || p->funcnum != PCI_FUNC(dev->pdev->devfn))
                return -EINVAL;

        p->irq = dev->pdev->irq;

        DRM_DEBUG("%d:%d:%d => IRQ %d\n", p->busnum, p->devnum, p->funcnum,
                  p->irq);

        return 0;
}

static void vblank_disable_fn(unsigned long arg)
{
        struct drm_device *dev = (struct drm_device *)arg;
        unsigned long irqflags;
        int i;

        if (!dev->vblank_disable_allowed)
                return;

        for (i = 0; i < dev->num_crtcs; i++) {
                spin_lock_irqsave(&dev->vbl_lock, irqflags);
                if (atomic_read(&dev->vblank_refcount[i]) == 0 &&
                    dev->vblank_enabled[i]) {
                        DRM_DEBUG("disabling vblank on crtc %d\n", i);
                        dev->last_vblank[i] =
                                dev->driver->get_vblank_counter(dev, i);
                        dev->driver->disable_vblank(dev, i);
                        dev->vblank_enabled[i] = 0;
                }
                spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
        }
}

static void drm_vblank_cleanup(struct drm_device *dev)
{
        /* Bail if the driver didn't call drm_vblank_init() */
        if (dev->num_crtcs == 0)
                return;

        del_timer(&dev->vblank_disable_timer);

        vblank_disable_fn((unsigned long)dev);

        drm_free(dev->vbl_queue, sizeof(*dev->vbl_queue) * dev->num_crtcs,
                 DRM_MEM_DRIVER);
        drm_free(dev->vbl_sigs, sizeof(*dev->vbl_sigs) * dev->num_crtcs,
                 DRM_MEM_DRIVER);
        drm_free(dev->_vblank_count, sizeof(*dev->_vblank_count) *
                 dev->num_crtcs, DRM_MEM_DRIVER);
        drm_free(dev->vblank_refcount, sizeof(*dev->vblank_refcount) *
                 dev->num_crtcs, DRM_MEM_DRIVER);
        drm_free(dev->vblank_enabled, sizeof(*dev->vblank_enabled) *
                 dev->num_crtcs, DRM_MEM_DRIVER);
        drm_free(dev->last_vblank, sizeof(*dev->last_vblank) * dev->num_crtcs,
                 DRM_MEM_DRIVER);
        drm_free(dev->vblank_inmodeset, sizeof(*dev->vblank_inmodeset) *
                 dev->num_crtcs, DRM_MEM_DRIVER);

        dev->num_crtcs = 0;
}

int drm_vblank_init(struct drm_device *dev, int num_crtcs)
{
        int i, ret = -ENOMEM;

        setup_timer(&dev->vblank_disable_timer, vblank_disable_fn,
                    (unsigned long)dev);
        spin_lock_init(&dev->vbl_lock);
        atomic_set(&dev->vbl_signal_pending, 0);
        dev->num_crtcs = num_crtcs;

        dev->vbl_queue = drm_alloc(sizeof(wait_queue_head_t) * num_crtcs,
                                   DRM_MEM_DRIVER);
        if (!dev->vbl_queue)
                goto err;

        dev->vbl_sigs = drm_alloc(sizeof(struct list_head) * num_crtcs,
                                  DRM_MEM_DRIVER);
        if (!dev->vbl_sigs)
                goto err;

        dev->_vblank_count = drm_alloc(sizeof(atomic_t) * num_crtcs,
                                      DRM_MEM_DRIVER);
        if (!dev->_vblank_count)
                goto err;

        dev->vblank_refcount = drm_alloc(sizeof(atomic_t) * num_crtcs,
                                         DRM_MEM_DRIVER);
        if (!dev->vblank_refcount)
                goto err;

        dev->vblank_enabled = drm_calloc(num_crtcs, sizeof(int),
                                         DRM_MEM_DRIVER);
        if (!dev->vblank_enabled)
                goto err;

        dev->last_vblank = drm_calloc(num_crtcs, sizeof(u32), DRM_MEM_DRIVER);
        if (!dev->last_vblank)
                goto err;

        dev->vblank_inmodeset = drm_calloc(num_crtcs, sizeof(int),
                                         DRM_MEM_DRIVER);
        if (!dev->vblank_inmodeset)
                goto err;

        /* Zero per-crtc vblank stuff */
        for (i = 0; i < num_crtcs; i++) {
                init_waitqueue_head(&dev->vbl_queue[i]);
                INIT_LIST_HEAD(&dev->vbl_sigs[i]);
                atomic_set(&dev->_vblank_count[i], 0);
                atomic_set(&dev->vblank_refcount[i], 0);
        }

        dev->vblank_disable_allowed = 0;

        return 0;

err:
        drm_vblank_cleanup(dev);
        return ret;
}
EXPORT_SYMBOL(drm_vblank_init);

/**
 * Install IRQ handler.
 *
 * \param dev DRM device.
 *
 * Initializes the IRQ related data. Installs the handler, calling the driver
 * \c drm_driver_irq_preinstall() and \c drm_driver_irq_postinstall() functions
 * before and after the installation.
 */
int drm_irq_install(struct drm_device *dev)
{
        int ret = 0;
        unsigned long sh_flags = 0;

        if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
                return -EINVAL;

        if (dev->pdev->irq == 0)
                return -EINVAL;

        mutex_lock(&dev->struct_mutex);

        /* Driver must have been initialized */
        if (!dev->dev_private) {
                mutex_unlock(&dev->struct_mutex);
                return -EINVAL;
        }

        if (dev->irq_enabled) {
                mutex_unlock(&dev->struct_mutex);
                return -EBUSY;
        }
        dev->irq_enabled = 1;
        mutex_unlock(&dev->struct_mutex);

        DRM_DEBUG("irq=%d\n", dev->pdev->irq);

        /* Before installing handler */
        dev->driver->irq_preinstall(dev);

        /* Install handler */
        if (drm_core_check_feature(dev, DRIVER_IRQ_SHARED))
                sh_flags = IRQF_SHARED;

        ret = request_irq(drm_dev_to_irq(dev), dev->driver->irq_handler,
                          sh_flags, dev->devname, dev);

        if (ret < 0) {
                mutex_lock(&dev->struct_mutex);
                dev->irq_enabled = 0;
                mutex_unlock(&dev->struct_mutex);
                return ret;
        }

        /* After installing handler */
        ret = dev->driver->irq_postinstall(dev);
        if (ret < 0) {
                mutex_lock(&dev->struct_mutex);
                dev->irq_enabled = 0;
                mutex_unlock(&dev->struct_mutex);
        }

        return ret;
}
EXPORT_SYMBOL(drm_irq_install);

/**
 * Uninstall the IRQ handler.
 *
 * \param dev DRM device.
 *
 * Calls the driver's \c drm_driver_irq_uninstall() function, and stops the irq.
 */
int drm_irq_uninstall(struct drm_device * dev)
{
        int irq_enabled;

        if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
                return -EINVAL;

        mutex_lock(&dev->struct_mutex);
        irq_enabled = dev->irq_enabled;
        dev->irq_enabled = 0;
        mutex_unlock(&dev->struct_mutex);

        if (!irq_enabled)
                return -EINVAL;

        DRM_DEBUG("irq=%d\n", dev->pdev->irq);

        dev->driver->irq_uninstall(dev);

        free_irq(dev->pdev->irq, dev);

        drm_vblank_cleanup(dev);

        dev->locked_tasklet_func = NULL;

        return 0;
}
EXPORT_SYMBOL(drm_irq_uninstall);

/**
 * IRQ control ioctl.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param arg user argument, pointing to a drm_control structure.
 * \return zero on success or a negative number on failure.
 *
 * Calls irq_install() or irq_uninstall() according to \p arg.
 */
int drm_control(struct drm_device *dev, void *data,
                struct drm_file *file_priv)
{
        struct drm_control *ctl = data;

        /* if we haven't irq we fallback for compatibility reasons - this used to be a separate function in drm_dma.h */


        switch (ctl->func) {
        case DRM_INST_HANDLER:
                if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
                        return 0;
                if (dev->if_version < DRM_IF_VERSION(1, 2) &&
                    ctl->irq != dev->pdev->irq)
                        return -EINVAL;
                return drm_irq_install(dev);
        case DRM_UNINST_HANDLER:
                if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
                        return 0;
                return drm_irq_uninstall(dev);
        default:
                return -EINVAL;
        }
}

/**
 * drm_vblank_count - retrieve "cooked" vblank counter value
 * @dev: DRM device
 * @crtc: which counter to retrieve
 *
 * Fetches the "cooked" vblank count value that represents the number of
 * vblank events since the system was booted, including lost events due to
 * modesetting activity.
 */
u32 drm_vblank_count(struct drm_device *dev, int crtc)
{
        return atomic_read(&dev->_vblank_count[crtc]);
}
EXPORT_SYMBOL(drm_vblank_count);

/**
 * drm_update_vblank_count - update the master vblank counter
 * @dev: DRM device
 * @crtc: counter to update
 *
 * Call back into the driver to update the appropriate vblank counter
 * (specified by @crtc).  Deal with wraparound, if it occurred, and
 * update the last read value so we can deal with wraparound on the next
 * call if necessary.
 *
 * Only necessary when going from off->on, to account for frames we
 * didn't get an interrupt for.
 *
 * Note: caller must hold dev->vbl_lock since this reads & writes
 * device vblank fields.
 */
static void drm_update_vblank_count(struct drm_device *dev, int crtc)
{
        u32 cur_vblank, diff;

        /*
         * Interrupts were disabled prior to this call, so deal with counter
         * wrap if needed.
         * NOTE!  It's possible we lost a full dev->max_vblank_count events
         * here if the register is small or we had vblank interrupts off for
         * a long time.
         */
        cur_vblank = dev->driver->get_vblank_counter(dev, crtc);
        diff = cur_vblank - dev->last_vblank[crtc];
        if (cur_vblank < dev->last_vblank[crtc]) {
                diff += dev->max_vblank_count;

                DRM_DEBUG("last_vblank[%d]=0x%x, cur_vblank=0x%x => diff=0x%x\n",
                          crtc, dev->last_vblank[crtc], cur_vblank, diff);
        }

        DRM_DEBUG("enabling vblank interrupts on crtc %d, missed %d\n",
                  crtc, diff);

        atomic_add(diff, &dev->_vblank_count[crtc]);
}

/**
 * drm_vblank_get - get a reference count on vblank events
 * @dev: DRM device
 * @crtc: which CRTC to own
 *
 * Acquire a reference count on vblank events to avoid having them disabled
 * while in use.
 *
 * RETURNS
 * Zero on success, nonzero on failure.
 */
int drm_vblank_get(struct drm_device *dev, int crtc)
{
        unsigned long irqflags;
        int ret = 0;

        spin_lock_irqsave(&dev->vbl_lock, irqflags);
        /* Going from 0->1 means we have to enable interrupts again */
        if (atomic_add_return(1, &dev->vblank_refcount[crtc]) == 1 &&
            !dev->vblank_enabled[crtc]) {
                ret = dev->driver->enable_vblank(dev, crtc);
                DRM_DEBUG("enabling vblank on crtc %d, ret: %d\n", crtc, ret);
                if (ret)
                        atomic_dec(&dev->vblank_refcount[crtc]);
                else {
                        dev->vblank_enabled[crtc] = 1;
                        drm_update_vblank_count(dev, crtc);
                }
        }
        spin_unlock_irqrestore(&dev->vbl_lock, irqflags);

        return ret;
}
EXPORT_SYMBOL(drm_vblank_get);

/**
 * drm_vblank_put - give up ownership of vblank events
 * @dev: DRM device
 * @crtc: which counter to give up
 *
 * Release ownership of a given vblank counter, turning off interrupts
 * if possible.
 */
void drm_vblank_put(struct drm_device *dev, int crtc)
{
        /* Last user schedules interrupt disable */
        if (atomic_dec_and_test(&dev->vblank_refcount[crtc]))
                mod_timer(&dev->vblank_disable_timer, jiffies + 5*DRM_HZ);
}
EXPORT_SYMBOL(drm_vblank_put);

/**
 * drm_modeset_ctl - handle vblank event counter changes across mode switch
 * @DRM_IOCTL_ARGS: standard ioctl arguments
 *
 * Applications should call the %_DRM_PRE_MODESET and %_DRM_POST_MODESET
 * ioctls around modesetting so that any lost vblank events are accounted for.
 *
 * Generally the counter will reset across mode sets.  If interrupts are
 * enabled around this call, we don't have to do anything since the counter
 * will have already been incremented.
 */
int drm_modeset_ctl(struct drm_device *dev, void *data,
                    struct drm_file *file_priv)
{
        struct drm_modeset_ctl *modeset = data;
        unsigned long irqflags;
        int crtc, ret = 0;

        /* If drm_vblank_init() hasn't been called yet, just no-op */
        if (!dev->num_crtcs)
                goto out;

        crtc = modeset->crtc;
        if (crtc >= dev->num_crtcs) {
                ret = -EINVAL;
                goto out;
        }

        /*
         * To avoid all the problems that might happen if interrupts
         * were enabled/disabled around or between these calls, we just
         * have the kernel take a reference on the CRTC (just once though
         * to avoid corrupting the count if multiple, mismatch calls occur),
         * so that interrupts remain enabled in the interim.
         */
        switch (modeset->cmd) {
        case _DRM_PRE_MODESET:
                if (!dev->vblank_inmodeset[crtc]) {
                        dev->vblank_inmodeset[crtc] = 1;
                        drm_vblank_get(dev, crtc);
                }
                break;
        case _DRM_POST_MODESET:
                if (dev->vblank_inmodeset[crtc]) {
                        spin_lock_irqsave(&dev->vbl_lock, irqflags);
                        dev->vblank_disable_allowed = 1;
                        dev->vblank_inmodeset[crtc] = 0;
                        spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
                        drm_vblank_put(dev, crtc);
                }
                break;
        default:
                ret = -EINVAL;
                break;
        }

out:
        return ret;
}

/**
 * Wait for VBLANK.
 *
 * \param inode device inode.
 * \param file_priv DRM file private.
 * \param cmd command.
 * \param data user argument, pointing to a drm_wait_vblank structure.
 * \return zero on success or a negative number on failure.
 *
 * Verifies the IRQ is installed.
 *
 * If a signal is requested checks if this task has already scheduled the same signal
 * for the same vblank sequence number - nothing to be done in
 * that case. If the number of tasks waiting for the interrupt exceeds 100 the
 * function fails. Otherwise adds a new entry to drm_device::vbl_sigs for this
 * task.
 *
 * If a signal is not requested, then calls vblank_wait().
 */
int drm_wait_vblank(struct drm_device *dev, void *data,
                    struct drm_file *file_priv)
{
        union drm_wait_vblank *vblwait = data;
        int ret = 0;
        unsigned int flags, seq, crtc;

        if ((!dev->pdev->irq) || (!dev->irq_enabled))
                return -EINVAL;

        if (vblwait->request.type &
            ~(_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK)) {
                DRM_ERROR("Unsupported type value 0x%x, supported mask 0x%x\n",
                          vblwait->request.type,
                          (_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK));
                return -EINVAL;
        }

        flags = vblwait->request.type & _DRM_VBLANK_FLAGS_MASK;
        crtc = flags & _DRM_VBLANK_SECONDARY ? 1 : 0;

        if (crtc >= dev->num_crtcs)
                return -EINVAL;

        ret = drm_vblank_get(dev, crtc);
        if (ret) {
                DRM_ERROR("failed to acquire vblank counter, %d\n", ret);
                return ret;
        }
        seq = drm_vblank_count(dev, crtc);

        switch (vblwait->request.type & _DRM_VBLANK_TYPES_MASK) {
        case _DRM_VBLANK_RELATIVE:
                vblwait->request.sequence += seq;
                vblwait->request.type &= ~_DRM_VBLANK_RELATIVE;
        case _DRM_VBLANK_ABSOLUTE:
                break;
        default:
                ret = -EINVAL;
                goto done;
        }

        if ((flags & _DRM_VBLANK_NEXTONMISS) &&
            (seq - vblwait->request.sequence) <= (1<<23)) {
                vblwait->request.sequence = seq + 1;
        }

        if (flags & _DRM_VBLANK_SIGNAL) {
                unsigned long irqflags;
                struct list_head *vbl_sigs = &dev->vbl_sigs[crtc];
                struct drm_vbl_sig *vbl_sig;

                spin_lock_irqsave(&dev->vbl_lock, irqflags);

                /* Check if this task has already scheduled the same signal
                 * for the same vblank sequence number; nothing to be done in
                 * that case
                 */
                list_for_each_entry(vbl_sig, vbl_sigs, head) {
                        if (vbl_sig->sequence == vblwait->request.sequence
                            && vbl_sig->info.si_signo ==
                            vblwait->request.signal
                            && vbl_sig->task == current) {
                                spin_unlock_irqrestore(&dev->vbl_lock,
                                                       irqflags);
                                vblwait->reply.sequence = seq;
                                goto done;
                        }
                }

                if (atomic_read(&dev->vbl_signal_pending) >= 100) {
                        spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
                        ret = -EBUSY;
                        goto done;
                }

                spin_unlock_irqrestore(&dev->vbl_lock, irqflags);

                vbl_sig = drm_calloc(1, sizeof(struct drm_vbl_sig),
                                     DRM_MEM_DRIVER);
                if (!vbl_sig) {
                        ret = -ENOMEM;
                        goto done;
                }

                /* Get a refcount on the vblank, which will be released by
                 * drm_vbl_send_signals().
                 */
                ret = drm_vblank_get(dev, crtc);
                if (ret) {
                        drm_free(vbl_sig, sizeof(struct drm_vbl_sig),
                                 DRM_MEM_DRIVER);
                        goto done;
                }

                atomic_inc(&dev->vbl_signal_pending);

                vbl_sig->sequence = vblwait->request.sequence;
                vbl_sig->info.si_signo = vblwait->request.signal;
                vbl_sig->task = current;

                spin_lock_irqsave(&dev->vbl_lock, irqflags);

                list_add_tail(&vbl_sig->head, vbl_sigs);

                spin_unlock_irqrestore(&dev->vbl_lock, irqflags);

                vblwait->reply.sequence = seq;
        } else {
                DRM_DEBUG("waiting on vblank count %d, crtc %d\n",
                          vblwait->request.sequence, crtc);
                DRM_WAIT_ON(ret, dev->vbl_queue[crtc], 3 * DRM_HZ,
                            ((drm_vblank_count(dev, crtc)
                              - vblwait->request.sequence) <= (1 << 23)));

                if (ret != -EINTR) {
                        struct timeval now;

                        do_gettimeofday(&now);

                        vblwait->reply.tval_sec = now.tv_sec;
                        vblwait->reply.tval_usec = now.tv_usec;
                        vblwait->reply.sequence = drm_vblank_count(dev, crtc);
                        DRM_DEBUG("returning %d to client\n",
                                  vblwait->reply.sequence);
                } else {
                        DRM_DEBUG("vblank wait interrupted by signal\n");
                }
        }

done:
        drm_vblank_put(dev, crtc);
        return ret;
}

/**
 * Send the VBLANK signals.
 *
 * \param dev DRM device.
 * \param crtc CRTC where the vblank event occurred
 *
 * Sends a signal for each task in drm_device::vbl_sigs and empties the list.
 *
 * If a signal is not requested, then calls vblank_wait().
 */
static void drm_vbl_send_signals(struct drm_device *dev, int crtc)
{
        struct drm_vbl_sig *vbl_sig, *tmp;
        struct list_head *vbl_sigs;
        unsigned int vbl_seq;
        unsigned long flags;

        spin_lock_irqsave(&dev->vbl_lock, flags);

        vbl_sigs = &dev->vbl_sigs[crtc];
        vbl_seq = drm_vblank_count(dev, crtc);

        list_for_each_entry_safe(vbl_sig, tmp, vbl_sigs, head) {
            if ((vbl_seq - vbl_sig->sequence) <= (1 << 23)) {
                vbl_sig->info.si_code = vbl_seq;
                send_sig_info(vbl_sig->info.si_signo,
                              &vbl_sig->info, vbl_sig->task);

                list_del(&vbl_sig->head);

                drm_free(vbl_sig, sizeof(*vbl_sig),
                         DRM_MEM_DRIVER);
                atomic_dec(&dev->vbl_signal_pending);
                drm_vblank_put(dev, crtc);
            }
        }

        spin_unlock_irqrestore(&dev->vbl_lock, flags);
}

/**
 * drm_handle_vblank - handle a vblank event
 * @dev: DRM device
 * @crtc: where this event occurred
 *
 * Drivers should call this routine in their vblank interrupt handlers to
 * update the vblank counter and send any signals that may be pending.
 */
void drm_handle_vblank(struct drm_device *dev, int crtc)
{
        atomic_inc(&dev->_vblank_count[crtc]);
        DRM_WAKEUP(&dev->vbl_queue[crtc]);
        drm_vbl_send_signals(dev, crtc);
}
EXPORT_SYMBOL(drm_handle_vblank);

/**
 * Tasklet wrapper function.
 *
 * \param data DRM device in disguise.
 *
 * Attempts to grab the HW lock and calls the driver callback on success. On
 * failure, leave the lock marked as contended so the callback can be called
 * from drm_unlock().
 */
static void drm_locked_tasklet_func(unsigned long data)
{
        struct drm_device *dev = (struct drm_device *)data;
        unsigned long irqflags;
        void (*tasklet_func)(struct drm_device *);
        
        spin_lock_irqsave(&dev->tasklet_lock, irqflags);
        tasklet_func = dev->locked_tasklet_func;
        spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);

        if (!tasklet_func ||
            !drm_lock_take(&dev->lock,
                           DRM_KERNEL_CONTEXT)) {
                return;
        }

        dev->lock.lock_time = jiffies;
        atomic_inc(&dev->counts[_DRM_STAT_LOCKS]);

        spin_lock_irqsave(&dev->tasklet_lock, irqflags);
        tasklet_func = dev->locked_tasklet_func;
        dev->locked_tasklet_func = NULL;
        spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
        
        if (tasklet_func != NULL)
                tasklet_func(dev);

        drm_lock_free(&dev->lock,
                      DRM_KERNEL_CONTEXT);
}

/**
 * Schedule a tasklet to call back a driver hook with the HW lock held.
 *
 * \param dev DRM device.
 * \param func Driver callback.
 *
 * This is intended for triggering actions that require the HW lock from an
 * interrupt handler. The lock will be grabbed ASAP after the interrupt handler
 * completes. Note that the callback may be called from interrupt or process
 * context, it must not make any assumptions about this. Also, the HW lock will
 * be held with the kernel context or any client context.
 */
void drm_locked_tasklet(struct drm_device *dev, void (*func)(struct drm_device *))
{
        unsigned long irqflags;
        static DECLARE_TASKLET(drm_tasklet, drm_locked_tasklet_func, 0);

        if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ) ||
            test_bit(TASKLET_STATE_SCHED, &drm_tasklet.state))
                return;

        spin_lock_irqsave(&dev->tasklet_lock, irqflags);

        if (dev->locked_tasklet_func) {
                spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);
                return;
        }

        dev->locked_tasklet_func = func;

        spin_unlock_irqrestore(&dev->tasklet_lock, irqflags);

        drm_tasklet.data = (unsigned long)dev;

        tasklet_hi_schedule(&drm_tasklet);
}
EXPORT_SYMBOL(drm_locked_tasklet);