ecore_drm2: Add a query for the next vblank time

I guess this is a feature, and we're deep in freeze, but:

a) this is critical for fixing T5462 properly without any side effects.
b) ecore_drm2 is all beta api
c) this should only affect wayland users

ref T5462

src/lib/ecore_drm2/Ecore_Drm2.h

@@ -1075,6 +1075,20 @@ EAPI Eina_Bool ecore_drm2_plane_fb_set(Ecore_Drm2_Plane *plane, Ecore_Drm2_Fb *f
  * @since 1.20
  */
 EAPI void ecore_drm2_fb_status_handler_set(Ecore_Drm2_Fb *fb, Ecore_Drm2_Fb_Status_Handler handler, void *data);
+
+/**
+ * Get the time of the last vblank
+ *
+ * Query the display hardware for the time of the last vblank.
+ *
+ * @param output
+ * @param sec
+ * @param usec
+ *
+ * @since 1.20
+ */
+EAPI Eina_Bool ecore_drm2_output_blanktime_get(Ecore_Drm2_Output *output, long *sec, long *usec);
+
 # endif
 
 #endif

src/lib/ecore_drm2/ecore_drm2.c

@@ -46,6 +46,7 @@ int (*sym_drmModePageFlip)(int fd, uint32_t crtc_id, uint32_t fb_id, uint32_t fl
 int (*sym_drmModeDirtyFB)(int fd, uint32_t bufferId, drmModeClipPtr clips, uint32_t num_clips) = NULL;
 int (*sym_drmModeCrtcSetGamma)(int fd, uint32_t crtc_id, uint32_t size, uint16_t *red, uint16_t *green, uint16_t *blue) = NULL;
 int (*sym_drmPrimeFDToHandle)(int fd, int prime_fd, uint32_t *handle) = NULL;
+int (*sym_drmWaitVBlank)(int fd, drmVBlank *vbl) = NULL;
 
 EAPI int ECORE_DRM2_EVENT_OUTPUT_CHANGED = -1;
 EAPI int ECORE_DRM2_EVENT_ACTIVATE = -1;
@@ -82,7 +83,7 @@ _ecore_drm2_link(void)
 
         SYM(drm_lib, drmIoctl);
         /* SYM(drm_lib, drmClose); */
-        /* SYM(drm_lib, drmWaitVBlank); */
+        SYM(drm_lib, drmWaitVBlank);
         SYM(drm_lib, drmHandleEvent);
         SYM(drm_lib, drmGetVersion);
         SYM(drm_lib, drmFreeVersion);

src/lib/ecore_drm2/ecore_drm2_outputs.c

@@ -1582,3 +1582,25 @@ ecore_drm2_output_subpixel_get(const Ecore_Drm2_Output *output)
    EINA_SAFETY_ON_NULL_RETURN_VAL(output, 0);
    return output->subpixel;
 }
+
+EAPI Eina_Bool
+ecore_drm2_output_blanktime_get(Ecore_Drm2_Output *output, long *sec, long *usec)
+{
+  drmVBlank v;
+  int ret;
+
+  EINA_SAFETY_ON_NULL_RETURN_VAL(output, EINA_FALSE);
+  EINA_SAFETY_ON_NULL_RETURN_VAL(sec, EINA_FALSE);
+  EINA_SAFETY_ON_NULL_RETURN_VAL(usec, EINA_FALSE);
+
+  memset(&v, 0, sizeof(v));
+  v.request.type = DRM_VBLANK_RELATIVE;
+  ret = sym_drmWaitVBlank(output->fd, &v);
+  if (ret) return EINA_FALSE;
+  if (v.reply.tval_sec < 0) return EINA_FALSE;
+  if (v.reply.tval_usec < 0) return EINA_FALSE;
+
+  *sec = v.reply.tval_sec;
+  *usec = v.reply.tval_usec;
+  return EINA_TRUE;
+}

src/lib/ecore_drm2/ecore_drm2_private.h

@@ -302,7 +302,7 @@ void _ecore_drm2_fb_deref(Ecore_Drm2_Fb *);
 void _ecore_drm2_fb_buffer_release(Ecore_Drm2_Output *output, Ecore_Drm2_Output_State *s);
 
 /* extern int (*sym_drmClose)(int fd); */
-/* extern int (*sym_drmWaitVBlank)(int fd, drmVBlank *vbl); */
+extern int (*sym_drmWaitVBlank)(int fd, drmVBlank *vbl);
 extern int (*sym_drmHandleEvent)(int fd, drmEventContext *evctx);
 extern void *(*sym_drmGetVersion)(int fd);
 extern void (*sym_drmFreeVersion)(void *drmver);