ecore_drm2: Add a panic mode to drm2_fb_release

Previously we'd call this only when we absolutely needed to, so it made
sense to always attempt to free a buffer, including ones on scanout or
pending flip.

However, it's useful to have a way to release the "next" only, so we can
do that before starting a render to free up the buffer that's never going
to be scanned out.

src/lib/ecore_drm2/Ecore_Drm2.h

@@ -829,16 +829,19 @@ EAPI void ecore_drm2_fb_busy_set(Ecore_Drm2_Fb *fb, Eina_Bool busy);
 /**
  * Try to force a framebuffer release for an output
  *
- * This tries to release the next, pending, or current buffer from
- * the output.  If successful there will be a release callback to
- * the registered handler, and the fb will no longer be flagged busy.
+ * This tries to release the next or optionally pending, or current
+ * buffer from the output.  If successful there will be a release callback
+ * to the registered handler, and the fb will no longer be flagged busy.
+ *
+ * Releasing buffers committed to scanout will potentially cause flicker,
+ * so this is only done when the panic flag is set.
  *
  * @param output The output to force release
- *
+ * @param panic Try to release even buffers committed to scanout
  * @ingroup Ecore_Drm2_Fb_Group
  * @since 1.19
  */
-EAPI void ecore_drm2_fb_release(Ecore_Drm2_Output *o);
+EAPI void ecore_drm2_fb_release(Ecore_Drm2_Output *o, Eina_Bool panic);
 
 /**
  * Set the user data for the output's page flip handler

src/lib/ecore_drm2/ecore_drm2_fb.c

@@ -456,7 +456,7 @@ ecore_drm2_fb_busy_set(Ecore_Drm2_Fb *fb, Eina_Bool busy)
 }
 
 EAPI void
-ecore_drm2_fb_release(Ecore_Drm2_Output *o)
+ecore_drm2_fb_release(Ecore_Drm2_Output *o, Eina_Bool panic)
 {
    EINA_SAFETY_ON_NULL_RETURN(o);
 
@@ -466,6 +466,7 @@ ecore_drm2_fb_release(Ecore_Drm2_Output *o)
         o->next = NULL;
         return;
      }
+   if (!panic) return;
 
    WRN("Buffer release request when no next buffer");
    /* If we have to release these we're going to see tearing.

src/modules/evas/engines/drm/evas_outbuf.c

@@ -249,7 +249,7 @@ _outbuf_fb_assign(Outbuf *ob)
    ob->priv.draw = _outbuf_fb_wait(ob);
    while (!ob->priv.draw)
      {
-        ecore_drm2_fb_release(ob->priv.output);
+        ecore_drm2_fb_release(ob->priv.output, EINA_TRUE);
         ob->priv.draw = _outbuf_fb_wait(ob);
      }
 

src/modules/evas/engines/gl_drm/evas_outbuf.c

@@ -96,7 +96,7 @@ _evas_outbuf_buffer_swap(Outbuf *ob)
    bo = gbm_surface_lock_front_buffer(ob->surface);
    if (!bo)
      {
-        ecore_drm2_fb_release(ob->priv.output);
+        ecore_drm2_fb_release(ob->priv.output, EINA_TRUE);
         bo = gbm_surface_lock_front_buffer(ob->surface);
      }
    if (bo) fb = _evas_outbuf_fb_get(ob, bo);