docs(display): mention how to manipulate the invalidated area (#6836)

docs/porting/display.rst

@@ -239,6 +239,31 @@ In full and direct modes, the buffer size should be large enough for the whole s
 As LVGL can not handle fractional width make sure to round the horizontal resolution to 8-
 (For example 90 to 96)
 
+Constraints on the Redrawn Area
+-------------------------------
+
+Some display controllers have specific requirements for the window area where the rendered image can be sent
+(e.g., `x1` must be even, and `x2` must be odd).
+
+In the case of monochrome displays, `x1` must be `Nx8`, and `x2` must be `Nx8 - 1`.
+(If the display uses `LV_COLOR_FORMAT_I1`, LVGL automatically applies this rounding. See :ref:`monochrome`.)
+
+The size of the invalidated (redrawn) area can be controlled as follows:
+
+.. code:: c
+
+    void rounder_event_cb(lv_event_t * e)
+    {
+        lv_area_t * a = lv_event_get_invalidated_area(e);
+
+        a->x1 = a->x1 & (~0x1); /* Ensure that x1 is even */
+        a->x2 = a->x2 | 0x1;    /* Ensure that x2 is odd */
+    }
+
+    ...
+
+    lv_display_add_event_cb(disp, rounder_event_cb, LV_EVENT_INVALIDATE_AREA, NULL);
+
 
 Tiled Rendering
 ---------------