DRM/KMS: Add Bail-Out Conditions for Loop.

[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 <drm/drmP.h>
#include "drm_trace.h"

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

#include <linux/vgaarb.h>
#include <linux/export.h>

/* Access macro for slots in vblank timestamp ringbuffer. */
#define vblanktimestamp(dev, crtc, count) ( \
        (dev)->_vblank_time[(crtc) * DRM_VBLANKTIME_RBSIZE + \
        ((count) % DRM_VBLANKTIME_RBSIZE)])

/* Retry timestamp calculation up to 3 times to satisfy
 * drm_timestamp_precision before giving up.
 */
#define DRM_TIMESTAMP_MAXRETRIES 3

/* Threshold in nanoseconds for detection of redundant
 * vblank irq in drm_handle_vblank(). 1 msec should be ok.
 */
#define DRM_REDUNDANT_VBLIRQ_THRESH_NS 1000000

/**
 * 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 (!dev->driver->bus->irq_by_busid)
                return -EINVAL;

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

        return dev->driver->bus->irq_by_busid(dev, p);
}

/*
 * Clear vblank timestamp buffer for a crtc.
 */
static void clear_vblank_timestamps(struct drm_device *dev, int crtc)
{
        memset(&dev->_vblank_time[crtc * DRM_VBLANKTIME_RBSIZE], 0,
                DRM_VBLANKTIME_RBSIZE * sizeof(struct timeval));
}

/*
 * Disable vblank irq's on crtc, make sure that last vblank count
 * of hardware and corresponding consistent software vblank counter
 * are preserved, even if there are any spurious vblank irq's after
 * disable.
 */
static void vblank_disable_and_save(struct drm_device *dev, int crtc)
{
        unsigned long irqflags;
        u32 vblcount;
        s64 diff_ns;
        int vblrc;
        struct timeval tvblank;
        int count = DRM_TIMESTAMP_MAXRETRIES;

        /* Prevent vblank irq processing while disabling vblank irqs,
         * so no updates of timestamps or count can happen after we've
         * disabled. Needed to prevent races in case of delayed irq's.
         */
        spin_lock_irqsave(&dev->vblank_time_lock, irqflags);

        dev->driver->disable_vblank(dev, crtc);
        dev->vblank_enabled[crtc] = 0;

        /* No further vblank irq's will be processed after
         * this point. Get current hardware vblank count and
         * vblank timestamp, repeat until they are consistent.
         *
         * FIXME: There is still a race condition here and in
         * drm_update_vblank_count() which can cause off-by-one
         * reinitialization of software vblank counter. If gpu
         * vblank counter doesn't increment exactly at the leading
         * edge of a vblank interval, then we can lose 1 count if
         * we happen to execute between start of vblank and the
         * delayed gpu counter increment.
         */
        do {
                dev->last_vblank[crtc] = dev->driver->get_vblank_counter(dev, crtc);
                vblrc = drm_get_last_vbltimestamp(dev, crtc, &tvblank, 0);
        } while (dev->last_vblank[crtc] != dev->driver->get_vblank_counter(dev, crtc) && (--count) && vblrc);

        if (!count)
                vblrc = 0;

        /* Compute time difference to stored timestamp of last vblank
         * as updated by last invocation of drm_handle_vblank() in vblank irq.
         */
        vblcount = atomic_read(&dev->_vblank_count[crtc]);
        diff_ns = timeval_to_ns(&tvblank) -
                  timeval_to_ns(&vblanktimestamp(dev, crtc, vblcount));

        /* If there is at least 1 msec difference between the last stored
         * timestamp and tvblank, then we are currently executing our
         * disable inside a new vblank interval, the tvblank timestamp
         * corresponds to this new vblank interval and the irq handler
         * for this vblank didn't run yet and won't run due to our disable.
         * Therefore we need to do the job of drm_handle_vblank() and
         * increment the vblank counter by one to account for this vblank.
         *
         * Skip this step if there isn't any high precision timestamp
         * available. In that case we can't account for this and just
         * hope for the best.
         */
        if ((vblrc > 0) && (abs64(diff_ns) > 1000000)) {
                atomic_inc(&dev->_vblank_count[crtc]);
                smp_mb__after_atomic_inc();
        }

        /* Invalidate all timestamps while vblank irq's are off. */
        clear_vblank_timestamps(dev, crtc);

        spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
}

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);
                        vblank_disable_and_save(dev, i);
                }
                spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
        }
}

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_sync(&dev->vblank_disable_timer);

        vblank_disable_fn((unsigned long)dev);

        kfree(dev->vbl_queue);
        kfree(dev->_vblank_count);
        kfree(dev->vblank_refcount);
        kfree(dev->vblank_enabled);
        kfree(dev->last_vblank);
        kfree(dev->last_vblank_wait);
        kfree(dev->vblank_inmodeset);
        kfree(dev->_vblank_time);

        dev->num_crtcs = 0;
}
EXPORT_SYMBOL(drm_vblank_cleanup);

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);
        spin_lock_init(&dev->vblank_time_lock);

        dev->num_crtcs = num_crtcs;

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

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

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

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

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

        dev->last_vblank_wait = kcalloc(num_crtcs, sizeof(u32), GFP_KERNEL);
        if (!dev->last_vblank_wait)
                goto err;

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

        dev->_vblank_time = kcalloc(num_crtcs * DRM_VBLANKTIME_RBSIZE,
                                    sizeof(struct timeval), GFP_KERNEL);
        if (!dev->_vblank_time)
                goto err;

        DRM_INFO("Supports vblank timestamp caching Rev 1 (10.10.2010).\n");

        /* Driver specific high-precision vblank timestamping supported? */
        if (dev->driver->get_vblank_timestamp)
                DRM_INFO("Driver supports precise vblank timestamp query.\n");
        else
                DRM_INFO("No driver support for vblank timestamp query.\n");

        /* Zero per-crtc vblank stuff */
        for (i = 0; i < num_crtcs; i++) {
                init_waitqueue_head(&dev->vbl_queue[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);

static void drm_irq_vgaarb_nokms(void *cookie, bool state)
{
        struct drm_device *dev = cookie;

        if (dev->driver->vgaarb_irq) {
                dev->driver->vgaarb_irq(dev, state);
                return;
        }

        if (!dev->irq_enabled)
                return;

        if (state) {
                if (dev->driver->irq_uninstall)
                        dev->driver->irq_uninstall(dev);
        } else {
                if (dev->driver->irq_preinstall)
                        dev->driver->irq_preinstall(dev);
                if (dev->driver->irq_postinstall)
                        dev->driver->irq_postinstall(dev);
        }
}

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

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

        if (drm_dev_to_irq(dev) == 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", drm_dev_to_irq(dev));

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

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

        if (dev->devname)
                irqname = dev->devname;
        else
                irqname = dev->driver->name;

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

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

        if (!drm_core_check_feature(dev, DRIVER_MODESET))
                vga_client_register(dev->pdev, (void *)dev, drm_irq_vgaarb_nokms, NULL);

        /* After installing handler */
        if (dev->driver->irq_postinstall)
                ret = dev->driver->irq_postinstall(dev);

        if (ret < 0) {
                mutex_lock(&dev->struct_mutex);
                dev->irq_enabled = 0;
                mutex_unlock(&dev->struct_mutex);
                if (!drm_core_check_feature(dev, DRIVER_MODESET))
                        vga_client_register(dev->pdev, NULL, NULL, NULL);
                free_irq(drm_dev_to_irq(dev), dev);
        }

        return ret;
}
EXPORT_SYMBOL(drm_irq_install);

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

        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);

        /*
         * Wake up any waiters so they don't hang.
         */
        if (dev->num_crtcs) {
                spin_lock_irqsave(&dev->vbl_lock, irqflags);
                for (i = 0; i < dev->num_crtcs; i++) {
                        DRM_WAKEUP(&dev->vbl_queue[i]);
                        dev->vblank_enabled[i] = 0;
                        dev->last_vblank[i] =
                                dev->driver->get_vblank_counter(dev, i);
                }
                spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
        }

        if (!irq_enabled)
                return -EINVAL;

        DRM_DEBUG("irq=%d\n", drm_dev_to_irq(dev));

        if (!drm_core_check_feature(dev, DRIVER_MODESET))
                vga_client_register(dev->pdev, NULL, NULL, NULL);

        if (dev->driver->irq_uninstall)
                dev->driver->irq_uninstall(dev);

        free_irq(drm_dev_to_irq(dev), dev);

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

/**
 * drm_calc_timestamping_constants - Calculate and
 * store various constants which are later needed by
 * vblank and swap-completion timestamping, e.g, by
 * drm_calc_vbltimestamp_from_scanoutpos().
 * They are derived from crtc's true scanout timing,
 * so they take things like panel scaling or other
 * adjustments into account.
 *
 * @crtc drm_crtc whose timestamp constants should be updated.
 *
 */
void drm_calc_timestamping_constants(struct drm_crtc *crtc)
{
        s64 linedur_ns = 0, pixeldur_ns = 0, framedur_ns = 0;
        u64 dotclock;

        /* Dot clock in Hz: */
        dotclock = (u64) crtc->hwmode.clock * 1000;

        /* Fields of interlaced scanout modes are only halve a frame duration.
         * Double the dotclock to get halve the frame-/line-/pixelduration.
         */
        if (crtc->hwmode.flags & DRM_MODE_FLAG_INTERLACE)
                dotclock *= 2;

        /* Valid dotclock? */
        if (dotclock > 0) {
                /* Convert scanline length in pixels and video dot clock to
                 * line duration, frame duration and pixel duration in
                 * nanoseconds:
                 */
                pixeldur_ns = (s64) div64_u64(1000000000, dotclock);
                linedur_ns  = (s64) div64_u64(((u64) crtc->hwmode.crtc_htotal *
                                              1000000000), dotclock);
                framedur_ns = (s64) crtc->hwmode.crtc_vtotal * linedur_ns;
        } else
                DRM_ERROR("crtc %d: Can't calculate constants, dotclock = 0!\n",
                          crtc->base.id);

        crtc->pixeldur_ns = pixeldur_ns;
        crtc->linedur_ns  = linedur_ns;
        crtc->framedur_ns = framedur_ns;

        DRM_DEBUG("crtc %d: hwmode: htotal %d, vtotal %d, vdisplay %d\n",
                  crtc->base.id, crtc->hwmode.crtc_htotal,
                  crtc->hwmode.crtc_vtotal, crtc->hwmode.crtc_vdisplay);
        DRM_DEBUG("crtc %d: clock %d kHz framedur %d linedur %d, pixeldur %d\n",
                  crtc->base.id, (int) dotclock/1000, (int) framedur_ns,
                  (int) linedur_ns, (int) pixeldur_ns);
}
EXPORT_SYMBOL(drm_calc_timestamping_constants);

/**
 * drm_calc_vbltimestamp_from_scanoutpos - helper routine for kms
 * drivers. Implements calculation of exact vblank timestamps from
 * given drm_display_mode timings and current video scanout position
 * of a crtc. This can be called from within get_vblank_timestamp()
 * implementation of a kms driver to implement the actual timestamping.
 *
 * Should return timestamps conforming to the OML_sync_control OpenML
 * extension specification. The timestamp corresponds to the end of
 * the vblank interval, aka start of scanout of topmost-leftmost display
 * pixel in the following video frame.
 *
 * Requires support for optional dev->driver->get_scanout_position()
 * in kms driver, plus a bit of setup code to provide a drm_display_mode
 * that corresponds to the true scanout timing.
 *
 * The current implementation only handles standard video modes. It
 * returns as no operation if a doublescan or interlaced video mode is
 * active. Higher level code is expected to handle this.
 *
 * @dev: DRM device.
 * @crtc: Which crtc's vblank timestamp to retrieve.
 * @max_error: Desired maximum allowable error in timestamps (nanosecs).
 *             On return contains true maximum error of timestamp.
 * @vblank_time: Pointer to struct timeval which should receive the timestamp.
 * @flags: Flags to pass to driver:
 *         0 = Default.
 *         DRM_CALLED_FROM_VBLIRQ = If function is called from vbl irq handler.
 * @refcrtc: drm_crtc* of crtc which defines scanout timing.
 *
 * Returns negative value on error, failure or if not supported in current
 * video mode:
 *
 * -EINVAL   - Invalid crtc.
 * -EAGAIN   - Temporary unavailable, e.g., called before initial modeset.
 * -ENOTSUPP - Function not supported in current display mode.
 * -EIO      - Failed, e.g., due to failed scanout position query.
 *
 * Returns or'ed positive status flags on success:
 *
 * DRM_VBLANKTIME_SCANOUTPOS_METHOD - Signal this method used for timestamping.
 * DRM_VBLANKTIME_INVBL - Timestamp taken while scanout was in vblank interval.
 *
 */
int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, int crtc,
                                          int *max_error,
                                          struct timeval *vblank_time,
                                          unsigned flags,
                                          struct drm_crtc *refcrtc)
{
        ktime_t stime, etime, mono_time_offset;
        struct timeval tv_etime;
        struct drm_display_mode *mode;
        int vbl_status, vtotal, vdisplay;
        int vpos, hpos, i;
        s64 framedur_ns, linedur_ns, pixeldur_ns, delta_ns, duration_ns;
        bool invbl;

        if (crtc < 0 || crtc >= dev->num_crtcs) {
                DRM_ERROR("Invalid crtc %d\n", crtc);
                return -EINVAL;
        }

        /* Scanout position query not supported? Should not happen. */
        if (!dev->driver->get_scanout_position) {
                DRM_ERROR("Called from driver w/o get_scanout_position()!?\n");
                return -EIO;
        }

        mode = &refcrtc->hwmode;
        vtotal = mode->crtc_vtotal;
        vdisplay = mode->crtc_vdisplay;

        /* Durations of frames, lines, pixels in nanoseconds. */
        framedur_ns = refcrtc->framedur_ns;
        linedur_ns  = refcrtc->linedur_ns;
        pixeldur_ns = refcrtc->pixeldur_ns;

        /* If mode timing undefined, just return as no-op:
         * Happens during initial modesetting of a crtc.
         */
        if (vtotal <= 0 || vdisplay <= 0 || framedur_ns == 0) {
                DRM_DEBUG("crtc %d: Noop due to uninitialized mode.\n", crtc);
                return -EAGAIN;
        }

        /* Get current scanout position with system timestamp.
         * Repeat query up to DRM_TIMESTAMP_MAXRETRIES times
         * if single query takes longer than max_error nanoseconds.
         *
         * This guarantees a tight bound on maximum error if
         * code gets preempted or delayed for some reason.
         */
        for (i = 0; i < DRM_TIMESTAMP_MAXRETRIES; i++) {
                /* Disable preemption to make it very likely to
                 * succeed in the first iteration even on PREEMPT_RT kernel.
                 */
                preempt_disable();

                /* Get system timestamp before query. */
                stime = ktime_get();

                /* Get vertical and horizontal scanout pos. vpos, hpos. */
                vbl_status = dev->driver->get_scanout_position(dev, crtc, &vpos, &hpos);

                /* Get system timestamp after query. */
                etime = ktime_get();
                if (!drm_timestamp_monotonic)
                        mono_time_offset = ktime_get_monotonic_offset();

                preempt_enable();

                /* Return as no-op if scanout query unsupported or failed. */
                if (!(vbl_status & DRM_SCANOUTPOS_VALID)) {
                        DRM_DEBUG("crtc %d : scanoutpos query failed [%d].\n",
                                  crtc, vbl_status);
                        return -EIO;
                }

                duration_ns = ktime_to_ns(etime) - ktime_to_ns(stime);

                /* Accept result with <  max_error nsecs timing uncertainty. */
                if (duration_ns <= (s64) *max_error)
                        break;
        }

        /* Noisy system timing? */
        if (i == DRM_TIMESTAMP_MAXRETRIES) {
                DRM_DEBUG("crtc %d: Noisy timestamp %d us > %d us [%d reps].\n",
                          crtc, (int) duration_ns/1000, *max_error/1000, i);
        }

        /* Return upper bound of timestamp precision error. */
        *max_error = (int) duration_ns;

        /* Check if in vblank area:
         * vpos is >=0 in video scanout area, but negative
         * within vblank area, counting down the number of lines until
         * start of scanout.
         */
        invbl = vbl_status & DRM_SCANOUTPOS_INVBL;

        /* Convert scanout position into elapsed time at raw_time query
         * since start of scanout at first display scanline. delta_ns
         * can be negative if start of scanout hasn't happened yet.
         */
        delta_ns = (s64) vpos * linedur_ns + (s64) hpos * pixeldur_ns;

        /* Is vpos outside nominal vblank area, but less than
         * 1/100 of a frame height away from start of vblank?
         * If so, assume this isn't a massively delayed vblank
         * interrupt, but a vblank interrupt that fired a few
         * microseconds before true start of vblank. Compensate
         * by adding a full frame duration to the final timestamp.
         * Happens, e.g., on ATI R500, R600.
         *
         * We only do this if DRM_CALLED_FROM_VBLIRQ.
         */
        if ((flags & DRM_CALLED_FROM_VBLIRQ) && !invbl &&
            ((vdisplay - vpos) < vtotal / 100)) {
                delta_ns = delta_ns - framedur_ns;

                /* Signal this correction as "applied". */
                vbl_status |= 0x8;
        }

        if (!drm_timestamp_monotonic)
                etime = ktime_sub(etime, mono_time_offset);

        /* save this only for debugging purposes */
        tv_etime = ktime_to_timeval(etime);
        /* Subtract time delta from raw timestamp to get final
         * vblank_time timestamp for end of vblank.
         */
        etime = ktime_sub_ns(etime, delta_ns);
        *vblank_time = ktime_to_timeval(etime);

        DRM_DEBUG("crtc %d : v %d p(%d,%d)@ %ld.%ld -> %ld.%ld [e %d us, %d rep]\n",
                  crtc, (int)vbl_status, hpos, vpos,
                  (long)tv_etime.tv_sec, (long)tv_etime.tv_usec,
                  (long)vblank_time->tv_sec, (long)vblank_time->tv_usec,
                  (int)duration_ns/1000, i);

        vbl_status = DRM_VBLANKTIME_SCANOUTPOS_METHOD;
        if (invbl)
                vbl_status |= DRM_VBLANKTIME_INVBL;

        return vbl_status;
}
EXPORT_SYMBOL(drm_calc_vbltimestamp_from_scanoutpos);

static struct timeval get_drm_timestamp(void)
{
        ktime_t now;

        now = ktime_get();
        if (!drm_timestamp_monotonic)
                now = ktime_sub(now, ktime_get_monotonic_offset());

        return ktime_to_timeval(now);
}

/**
 * drm_get_last_vbltimestamp - retrieve raw timestamp for the most recent
 * vblank interval.
 *
 * @dev: DRM device
 * @crtc: which crtc's vblank timestamp to retrieve
 * @tvblank: Pointer to target struct timeval which should receive the timestamp
 * @flags: Flags to pass to driver:
 *         0 = Default.
 *         DRM_CALLED_FROM_VBLIRQ = If function is called from vbl irq handler.
 *
 * Fetches the system timestamp corresponding to the time of the most recent
 * vblank interval on specified crtc. May call into kms-driver to
 * compute the timestamp with a high-precision GPU specific method.
 *
 * Returns zero if timestamp originates from uncorrected do_gettimeofday()
 * call, i.e., it isn't very precisely locked to the true vblank.
 *
 * Returns non-zero if timestamp is considered to be very precise.
 */
u32 drm_get_last_vbltimestamp(struct drm_device *dev, int crtc,
                              struct timeval *tvblank, unsigned flags)
{
        int ret;

        /* Define requested maximum error on timestamps (nanoseconds). */
        int max_error = (int) drm_timestamp_precision * 1000;

        /* Query driver if possible and precision timestamping enabled. */
        if (dev->driver->get_vblank_timestamp && (max_error > 0)) {
                ret = dev->driver->get_vblank_timestamp(dev, crtc, &max_error,
                                                        tvblank, flags);
                if (ret > 0)
                        return (u32) ret;
        }

        /* GPU high precision timestamp query unsupported or failed.
         * Return current monotonic/gettimeofday timestamp as best estimate.
         */
        *tvblank = get_drm_timestamp();

        return 0;
}
EXPORT_SYMBOL(drm_get_last_vbltimestamp);

/**
 * 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_vblank_count_and_time - retrieve "cooked" vblank counter value
 * and the system timestamp corresponding to that vblank counter value.
 *
 * @dev: DRM device
 * @crtc: which counter to retrieve
 * @vblanktime: Pointer to struct timeval to receive the vblank timestamp.
 *
 * 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. Returns corresponding system timestamp of the time
 * of the vblank interval that corresponds to the current value vblank counter
 * value.
 */
u32 drm_vblank_count_and_time(struct drm_device *dev, int crtc,
                              struct timeval *vblanktime)
{
        u32 cur_vblank;

        /* Read timestamp from slot of _vblank_time ringbuffer
         * that corresponds to current vblank count. Retry if
         * count has incremented during readout. This works like
         * a seqlock.
         */
        do {
                cur_vblank = atomic_read(&dev->_vblank_count[crtc]);
                *vblanktime = vblanktimestamp(dev, crtc, cur_vblank);
                smp_rmb();
        } while (cur_vblank != atomic_read(&dev->_vblank_count[crtc]));

        return cur_vblank;
}
EXPORT_SYMBOL(drm_vblank_count_and_time);

static void send_vblank_event(struct drm_device *dev,
                struct drm_pending_vblank_event *e,
                unsigned long seq, struct timeval *now)
{
        WARN_ON_SMP(!spin_is_locked(&dev->event_lock));
        e->event.sequence = seq;
        e->event.tv_sec = now->tv_sec;
        e->event.tv_usec = now->tv_usec;

        list_add_tail(&e->base.link,
                      &e->base.file_priv->event_list);
        wake_up_interruptible(&e->base.file_priv->event_wait);
        trace_drm_vblank_event_delivered(e->base.pid, e->pipe,
                                         e->event.sequence);
}

/**
 * drm_send_vblank_event - helper to send vblank event after pageflip
 * @dev: DRM device
 * @crtc: CRTC in question
 * @e: the event to send
 *
 * Updates sequence # and timestamp on event, and sends it to userspace.
 * Caller must hold event lock.
 */
void drm_send_vblank_event(struct drm_device *dev, int crtc,
                struct drm_pending_vblank_event *e)
{
        struct timeval now;
        unsigned int seq;
        if (crtc >= 0) {
                seq = drm_vblank_count_and_time(dev, crtc, &now);
        } else {
                seq = 0;

                now = get_drm_timestamp();
        }
        send_vblank_event(dev, e, seq, &now);
}
EXPORT_SYMBOL(drm_send_vblank_event);

/**
 * 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, tslot, rc;
        struct timeval t_vblank;

        /*
         * 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.
         *
         * We repeat the hardware vblank counter & timestamp query until
         * we get consistent results. This to prevent races between gpu
         * updating its hardware counter while we are retrieving the
         * corresponding vblank timestamp.
         */
        do {
                cur_vblank = dev->driver->get_vblank_counter(dev, crtc);
                rc = drm_get_last_vbltimestamp(dev, crtc, &t_vblank, 0);
        } while (cur_vblank != dev->driver->get_vblank_counter(dev, crtc));

        /* Deal with counter wrap */
        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);

        /* Reinitialize corresponding vblank timestamp if high-precision query
         * available. Skip this step if query unsupported or failed. Will
         * reinitialize delayed at next vblank interrupt in that case.
         */
        if (rc) {
                tslot = atomic_read(&dev->_vblank_count[crtc]) + diff;
                vblanktimestamp(dev, crtc, tslot) = t_vblank;
        }

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

/**
 * 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, irqflags2;
        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) {
                spin_lock_irqsave(&dev->vblank_time_lock, irqflags2);
                if (!dev->vblank_enabled[crtc]) {
                        /* Enable vblank irqs under vblank_time_lock protection.
                         * All vblank count & timestamp updates are held off
                         * until we are done reinitializing master counter and
                         * timestamps. Filtercode in drm_handle_vblank() will
                         * prevent double-accounting of same vblank interval.
                         */
                        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->vblank_time_lock, irqflags2);
        } else {
                if (!dev->vblank_enabled[crtc]) {
                        atomic_dec(&dev->vblank_refcount[crtc]);
                        ret = -EINVAL;
                }
        }
        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. Disable interrupts after drm_vblank_offdelay milliseconds.
 */
void drm_vblank_put(struct drm_device *dev, int crtc)
{
        BUG_ON(atomic_read(&dev->vblank_refcount[crtc]) == 0);

        /* Last user schedules interrupt disable */
        if (atomic_dec_and_test(&dev->vblank_refcount[crtc]) &&
            (drm_vblank_offdelay > 0))
                mod_timer(&dev->vblank_disable_timer,
                          jiffies + ((drm_vblank_offdelay * DRM_HZ)/1000));
}
EXPORT_SYMBOL(drm_vblank_put);

/**
 * drm_vblank_off - disable vblank events on a CRTC
 * @dev: DRM device
 * @crtc: CRTC in question
 *
 * Caller must hold event lock.
 */
void drm_vblank_off(struct drm_device *dev, int crtc)
{
        struct drm_pending_vblank_event *e, *t;
        struct timeval now;
        unsigned long irqflags;
        unsigned int seq;

        spin_lock_irqsave(&dev->vbl_lock, irqflags);
        vblank_disable_and_save(dev, crtc);
        DRM_WAKEUP(&dev->vbl_queue[crtc]);

        /* Send any queued vblank events, lest the natives grow disquiet */
        seq = drm_vblank_count_and_time(dev, crtc, &now);
        list_for_each_entry_safe(e, t, &dev->vblank_event_list, base.link) {
                if (e->pipe != crtc)
                        continue;
                DRM_DEBUG("Sending premature vblank event on disable: \
                          wanted %d, current %d\n",
                          e->event.sequence, seq);
                list_del(&e->base.link);
                drm_vblank_put(dev, e->pipe);
                send_vblank_event(dev, e, seq, &now);
        }

        spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
}
EXPORT_SYMBOL(drm_vblank_off);

/**
 * drm_vblank_pre_modeset - account for vblanks across mode sets
 * @dev: DRM device
 * @crtc: CRTC in question
 *
 * Account for vblank events across mode setting events, which will likely
 * reset the hardware frame counter.
 */
void drm_vblank_pre_modeset(struct drm_device *dev, int crtc)
{
        /* vblank is not initialized (IRQ not installed ?) */
        if (!dev->num_crtcs)
                return;
        /*
         * 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.
         */
        if (!dev->vblank_inmodeset[crtc]) {
                dev->vblank_inmodeset[crtc] = 0x1;
                if (drm_vblank_get(dev, crtc) == 0)
                        dev->vblank_inmodeset[crtc] |= 0x2;
        }
}
EXPORT_SYMBOL(drm_vblank_pre_modeset);

void drm_vblank_post_modeset(struct drm_device *dev, int crtc)
{
        unsigned long irqflags;

        if (dev->vblank_inmodeset[crtc]) {
                spin_lock_irqsave(&dev->vbl_lock, irqflags);
                dev->vblank_disable_allowed = 1;
                spin_unlock_irqrestore(&dev->vbl_lock, irqflags);

                if (dev->vblank_inmodeset[crtc] & 0x2)
                        drm_vblank_put(dev, crtc);

                dev->vblank_inmodeset[crtc] = 0;
        }
}
EXPORT_SYMBOL(drm_vblank_post_modeset);

/**
 * 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 int crtc;

        /* If drm_vblank_init() hasn't been called yet, just no-op */
        if (!dev->num_crtcs)
                return 0;

        /* KMS drivers handle this internally */
        if (drm_core_check_feature(dev, DRIVER_MODESET))
                return 0;

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

        switch (modeset->cmd) {
        case _DRM_PRE_MODESET:
                drm_vblank_pre_modeset(dev, crtc);
                break;
        case _DRM_POST_MODESET:
                drm_vblank_post_modeset(dev, crtc);
                break;
        default:
                return -EINVAL;
        }

        return 0;
}

static int drm_queue_vblank_event(struct drm_device *dev, int pipe,
                                  union drm_wait_vblank *vblwait,
                                  struct drm_file *file_priv)
{
        struct drm_pending_vblank_event *e;
        struct timeval now;
        unsigned long flags;
        unsigned int seq;
        int ret;

        e = kzalloc(sizeof *e, GFP_KERNEL);
        if (e == NULL) {
                ret = -ENOMEM;
                goto err_put;
        }

        e->pipe = pipe;
        e->base.pid = current->pid;
        e->event.base.type = DRM_EVENT_VBLANK;
        e->event.base.length = sizeof e->event;
        e->event.user_data = vblwait->request.signal;
        e->base.event = &e->event.base;
        e->base.file_priv = file_priv;
        e->base.destroy = (void (*) (struct drm_pending_event *)) kfree;

        spin_lock_irqsave(&dev->event_lock, flags);

        if (file_priv->event_space < sizeof e->event) {
                ret = -EBUSY;
                goto err_unlock;
        }

        file_priv->event_space -= sizeof e->event;
        seq = drm_vblank_count_and_time(dev, pipe, &now);

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

        DRM_DEBUG("event on vblank count %d, current %d, crtc %d\n",
                  vblwait->request.sequence, seq, pipe);

        trace_drm_vblank_event_queued(current->pid, pipe,
                                      vblwait->request.sequence);

        e->event.sequence = vblwait->request.sequence;
        if ((seq - vblwait->request.sequence) <= (1 << 23)) {
                drm_vblank_put(dev, pipe);
                send_vblank_event(dev, e, seq, &now);
                vblwait->reply.sequence = seq;
        } else {
                /* drm_handle_vblank_events will call drm_vblank_put */
                list_add_tail(&e->base.link, &dev->vblank_event_list);
                vblwait->reply.sequence = vblwait->request.sequence;
        }

        spin_unlock_irqrestore(&dev->event_lock, flags);

        return 0;

err_unlock:
        spin_unlock_irqrestore(&dev->event_lock, flags);
        kfree(e);
err_put:
        drm_vblank_put(dev, pipe);
        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.
 *
 * This function enables the vblank interrupt on the pipe requested, then
 * sleeps waiting for the requested sequence number to occur, and drops
 * the vblank interrupt refcount afterwards. (vblank irq disable follows that
 * after a timeout with no further vblank waits scheduled).
 */
int drm_wait_vblank(struct drm_device *dev, void *data,
                    struct drm_file *file_priv)
{
        union drm_wait_vblank *vblwait = data;
        int ret;
        unsigned int flags, seq, crtc, high_crtc;

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

        if (vblwait->request.type & _DRM_VBLANK_SIGNAL)
                return -EINVAL;

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

        flags = vblwait->request.type & _DRM_VBLANK_FLAGS_MASK;
        high_crtc = (vblwait->request.type & _DRM_VBLANK_HIGH_CRTC_MASK);
        if (high_crtc)
                crtc = high_crtc >> _DRM_VBLANK_HIGH_CRTC_SHIFT;
        else
                crtc = flags & _DRM_VBLANK_SECONDARY ? 1 : 0;
        if (crtc >= dev->num_crtcs)
                return -EINVAL;

        ret = drm_vblank_get(dev, crtc);
        if (ret) {
                DRM_DEBUG("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_EVENT) {
                /* must hold on to the vblank ref until the event fires
                 * drm_vblank_put will be called asynchronously
                 */
                return drm_queue_vblank_event(dev, crtc, vblwait, file_priv);
        }

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

        DRM_DEBUG("waiting on vblank count %d, crtc %d\n",
                  vblwait->request.sequence, crtc);
        dev->last_vblank_wait[crtc] = vblwait->request.sequence;
        DRM_WAIT_ON(ret, dev->vbl_queue[crtc], 3 * DRM_HZ,
                    (((drm_vblank_count(dev, crtc) -
                       vblwait->request.sequence) <= (1 << 23)) ||
                     !dev->irq_enabled));

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

                vblwait->reply.sequence = drm_vblank_count_and_time(dev, crtc, &now);
                vblwait->reply.tval_sec = now.tv_sec;
                vblwait->reply.tval_usec = now.tv_usec;

                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;
}

static void drm_handle_vblank_events(struct drm_device *dev, int crtc)
{
        struct drm_pending_vblank_event *e, *t;
        struct timeval now;
        unsigned long flags;
        unsigned int seq;

        seq = drm_vblank_count_and_time(dev, crtc, &now);

        spin_lock_irqsave(&dev->event_lock, flags);

        list_for_each_entry_safe(e, t, &dev->vblank_event_list, base.link) {
                if (e->pipe != crtc)
                        continue;
                if ((seq - e->event.sequence) > (1<<23))
                        continue;

                DRM_DEBUG("vblank event on %d, current %d\n",
                          e->event.sequence, seq);

                list_del(&e->base.link);
                drm_vblank_put(dev, e->pipe);
                send_vblank_event(dev, e, seq, &now);
        }

        spin_unlock_irqrestore(&dev->event_lock, flags);

        trace_drm_vblank_event(crtc, seq);
}

/**
 * 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.
 */
bool drm_handle_vblank(struct drm_device *dev, int crtc)
{
        u32 vblcount;
        s64 diff_ns;
        struct timeval tvblank;
        unsigned long irqflags;

        if (!dev->num_crtcs)
                return false;

        /* Need timestamp lock to prevent concurrent execution with
         * vblank enable/disable, as this would cause inconsistent
         * or corrupted timestamps and vblank counts.
         */
        spin_lock_irqsave(&dev->vblank_time_lock, irqflags);

        /* Vblank irq handling disabled. Nothing to do. */
        if (!dev->vblank_enabled[crtc]) {
                spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
                return false;
        }

        /* Fetch corresponding timestamp for this vblank interval from
         * driver and store it in proper slot of timestamp ringbuffer.
         */

        /* Get current timestamp and count. */
        vblcount = atomic_read(&dev->_vblank_count[crtc]);
        drm_get_last_vbltimestamp(dev, crtc, &tvblank, DRM_CALLED_FROM_VBLIRQ);

        /* Compute time difference to timestamp of last vblank */
        diff_ns = timeval_to_ns(&tvblank) -
                  timeval_to_ns(&vblanktimestamp(dev, crtc, vblcount));

        /* Update vblank timestamp and count if at least
         * DRM_REDUNDANT_VBLIRQ_THRESH_NS nanoseconds
         * difference between last stored timestamp and current
         * timestamp. A smaller difference means basically
         * identical timestamps. Happens if this vblank has
         * been already processed and this is a redundant call,
         * e.g., due to spurious vblank interrupts. We need to
         * ignore those for accounting.
         */
        if (abs64(diff_ns) > DRM_REDUNDANT_VBLIRQ_THRESH_NS) {
                /* Store new timestamp in ringbuffer. */
                vblanktimestamp(dev, crtc, vblcount + 1) = tvblank;

                /* Increment cooked vblank count. This also atomically commits
                 * the timestamp computed above.
                 */
                smp_mb__before_atomic_inc();
                atomic_inc(&dev->_vblank_count[crtc]);
                smp_mb__after_atomic_inc();
        } else {
                DRM_DEBUG("crtc %d: Redundant vblirq ignored. diff_ns = %d\n",
                          crtc, (int) diff_ns);
        }

        DRM_WAKEUP(&dev->vbl_queue[crtc]);
        drm_handle_vblank_events(dev, crtc);

        spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
        return true;
}
EXPORT_SYMBOL(drm_handle_vblank);