+ /* If this happens to execute within the "virtually extended" vblank
+ * interval before the start of the real vblank interval then it needs
+ * to delay programming the mmio flip until the real vblank is entered.
+ * This prevents completing a flip too early due to the way we fudge
+ * our vblank counter and vblank timestamps in order to work around the
+ * problem that the hw fires vblank interrupts before actual start of
+ * vblank (when line buffer refilling is done for a frame). It
+ * complements the fudging logic in radeon_get_crtc_scanoutpos() for
+ * timestamping and radeon_get_vblank_counter_kms() for vblank counts.
+ *
+ * In practice this won't execute very often unless on very fast
+ * machines because the time window for this to happen is very small.
+ */
+ while (radeon_crtc->enabled && --repcnt) {
+ /* GET_DISTANCE_TO_VBLANKSTART returns distance to real vblank
+ * start in hpos, and to the "fudged earlier" vblank start in
+ * vpos.
+ */
+ stat = radeon_get_crtc_scanoutpos(rdev->ddev, work->crtc_id,
+ GET_DISTANCE_TO_VBLANKSTART,
+ &vpos, &hpos, NULL, NULL,
+ &crtc->hwmode);
+
+ if ((stat & (DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE)) !=
+ (DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE) ||
+ !(vpos >= 0 && hpos <= 0))
+ break;
+
+ /* Sleep at least until estimated real start of hw vblank */
+ min_udelay = (-hpos + 1) * max(vblank->linedur_ns / 1000, 5);
+ if (min_udelay > vblank->framedur_ns / 2000) {
+ /* Don't wait ridiculously long - something is wrong */
+ repcnt = 0;
+ break;
+ }
+ spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
+ usleep_range(min_udelay, 2 * min_udelay);
+ spin_lock_irqsave(&crtc->dev->event_lock, flags);
+ };
+
+ if (!repcnt)
+ DRM_DEBUG_DRIVER("Delay problem on crtc %d: min_udelay %d, "
+ "framedur %d, linedur %d, stat %d, vpos %d, "
+ "hpos %d\n", work->crtc_id, min_udelay,
+ vblank->framedur_ns / 1000,
+ vblank->linedur_ns / 1000, stat, vpos, hpos);
+