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	if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))

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;

	}

	return -EIO;

}

EXPORT_SYMBOL(drm_calc_vbltimestamp_from_scanoutpos);