zephyr: allow placing LVGL rendering buffers into custom section

Some applications may want to locate LVGL rendering buffers in a custom
memory location, such as tightly coupled or external memory. To
facilitate this, add a Kconfig CONFIG_LV_Z_VBD_CUSTOM_SECTION, which
when set will locate the LVGL rendering buffers in a section labelled as
".lvgl_buf". This section can then be located in a custom memory region
by the application.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>

zephyr/Kconfig.memory

@@ -83,6 +83,14 @@ config LV_Z_VDB_ALIGN
 	  buffer may be accessed as a uint8_t *, uint16_t *, or uint32_t *,
 	  so buffer must be aligned to prevent unaligned memory access
 
+config LV_Z_VBD_CUSTOM_SECTION
+	bool "Link rendering buffers to custom section"
+	depends on LV_Z_BUFFER_ALLOC_STATIC
+	help
+	  Place LVGL rendering buffers in custom section, with tag ".lvgl_buf".
+	  This can be used by custom linker scripts to relocate the LVGL
+	  rendering buffers to a custom location, such as tightly coupled or
+	  external memory.
 choice
 	prompt "Rendering Buffer Allocation"
 	default LV_Z_BUFFER_ALLOC_STATIC

zephyr/lvgl.c

@@ -47,10 +47,19 @@ static lv_disp_draw_buf_t disp_buf;
  * uint16_t * or uint32_t *, therefore buffer needs to be aligned accordingly to
  * prevent unaligned memory accesses.
  */
-static uint8_t buf0[BUFFER_SIZE] __aligned(CONFIG_LV_Z_VDB_ALIGN);
+static uint8_t buf0[BUFFER_SIZE]
+#ifdef CONFIG_LV_Z_VBD_CUSTOM_SECTION
+	Z_GENERIC_SECTION(.lvgl_buf)
+#endif
+	__aligned(CONFIG_LV_Z_VDB_ALIGN);
+
 #ifdef CONFIG_LV_Z_DOUBLE_VDB
-static uint8_t buf1[BUFFER_SIZE] __aligned(CONFIG_LV_Z_VDB_ALIGN);
+static uint8_t buf1[BUFFER_SIZE]
+#ifdef CONFIG_LV_Z_VBD_CUSTOM_SECTION
+	Z_GENERIC_SECTION(.lvgl_buf)
 #endif
+	__aligned(CONFIG_LV_Z_VDB_ALIGN);
+#endif /* CONFIG_LV_Z_DOUBLE_VDB */
 
 #endif /* CONFIG_LV_Z_BUFFER_ALLOC_STATIC */