Update buffer size docs

components/lvgl/index.rst

@@ -195,7 +195,23 @@ The following configuration variables apply to the main ``lvgl`` component, in o
 
 See :ref:`lvgl-cookbook-navigator` in the Cookbook for an example which demonstrates how to implement a page navigation bar at the bottom of the screen.
 
-.. _lgvgl-multi-conf:
+
+Choosing a buffer size
+**********************
+
+The ``buffer_size`` option is a percentage of the display size. For example, if you have a 320x240 display, the buffer size is ``320 * 240 * 2`` bytes (for RGB565) = ``153600`` bytes. If you set the buffer size to ``50%``,
+then the buffer will be ``76800`` bytes. If you set it to ``25%``, then the buffer will be ``38400`` bytes. The default value is ``100%``.
+
+When using larger displays on devices with limited RAM (i.e. no PSRAM), you may need to reduce the buffer size to avoid running out of RAM.
+A failure to allocate a buffer will result in an error message in the log and the LVGL component being marked "Failed".
+
+Generally speaking a larger buffer will provide better performance, but the effect of reducing the buffer size from 100% is not as bad as you might think. The LVGL library is designed to be efficient and will only redraw the parts of the screen that have changed.
+
+A buffer size less than 100% can also be useful when PSRAM *is* available to *improve* performance. In this case a buffer size of 12% is recommended, and it will be allocated in internal
+RAM if possible, which will increase the speed of display redraws, since internal RAM is much faster to access than PSRAM.
+This may however reduce the internal RAM available for other components. A buffer size greater than 25% will be always allocated in PSRAM if available.
+
+.. _lvgl-multi-conf:
 
 
 Multiple LVGL configurations