+ /* The hw increments its frame counter at start of vsync, not at start
+ * of vblank, as is required by DRM core vblank counter handling.
+ * Cook the hw count here to make it appear to the caller as if it
+ * incremented at start of vblank. We measure distance to start of
+ * vblank in vpos. vpos therefore will be >= 0 between start of vblank
+ * and start of vsync, so vpos >= 0 means to bump the hw frame counter
+ * result by 1 to give the proper appearance to caller.
+ */
+ if (rdev->mode_info.crtcs[crtc]) {
+ /* Repeat readout if needed to provide stable result if
+ * we cross start of vsync during the queries.
+ */
+ do {
+ count = radeon_get_vblank_counter(rdev, crtc);
+ /* Ask radeon_get_crtc_scanoutpos to return vpos as
+ * distance to start of vblank, instead of regular
+ * vertical scanout pos.
+ */
+ stat = radeon_get_crtc_scanoutpos(
+ dev, crtc, GET_DISTANCE_TO_VBLANKSTART,
+ &vpos, &hpos, NULL, NULL,
+ &rdev->mode_info.crtcs[crtc]->base.hwmode);
+ } while (count != radeon_get_vblank_counter(rdev, crtc));
+
+ if (((stat & (DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE)) !=
+ (DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE))) {
+ DRM_DEBUG_VBL("Query failed! stat %d\n", stat);
+ }
+ else {
+ DRM_DEBUG_VBL("crtc %d: dist from vblank start %d\n",
+ crtc, vpos);
+
+ /* Bump counter if we are at >= leading edge of vblank,
+ * but before vsync where vpos would turn negative and
+ * the hw counter really increments.
+ */
+ if (vpos >= 0)
+ count++;
+ }
+ }
+ else {
+ /* Fallback to use value as is. */
+ count = radeon_get_vblank_counter(rdev, crtc);
+ DRM_DEBUG_VBL("NULL mode info! Returned count may be wrong.\n");
+ }
+
+ return count;