boards: imx93_evk: document the configuration of board muxes

Document the added board level driver to control EXP_SEL muxes

Signed-off-by: Chekhov Ma <[email protected]>

Author: CkovMk

boards/nxp/imx93_evk/board.c

@@ -11,8 +11,7 @@
 
 LOG_MODULE_REGISTER(board_control, CONFIG_BOARD_MIMX93_EVK_LOG_LEVEL);
 
-#if DT_HAS_COMPAT_STATUS_OKAY(imx93evk_exp_sel) && \
-	IS_ENABLED(CONFIG_BOARD_MIMX93_EVK_EXP_SEL_INIT)
+#if DT_HAS_COMPAT_STATUS_OKAY(imx93evk_exp_sel) && IS_ENABLED(CONFIG_BOARD_MIMX93_EVK_EXP_SEL_INIT)
 
 #define BOARD_EXP_SEL_NODE DT_COMPAT_GET_ANY_STATUS_OKAY(imx93evk_exp_sel)
 
@@ -22,8 +21,7 @@ LOG_MODULE_REGISTER(board_control, CONFIG_BOARD_MIMX93_EVK_LOG_LEVEL);
 static int board_init_exp_sel(void)
 {
 	int rc = 0;
-	const struct gpio_dt_spec mux =
-		GPIO_DT_SPEC_GET(BOARD_EXP_SEL_NODE, mux_gpios);
+	const struct gpio_dt_spec mux = GPIO_DT_SPEC_GET(BOARD_EXP_SEL_NODE, mux_gpios);
 	uint32_t pin_state = DT_ENUM_IDX(BOARD_EXP_SEL_NODE, mux);
 
 	if (!gpio_is_ready_dt(&mux)) {
@@ -43,10 +41,8 @@ static int board_init_exp_sel(void)
 		LOG_ERR("Write EXP_SEL Pin error %d", rc);
 		return rc;
 	}
-	LOG_INF("EXP_SEL mux %c with priority %d",
-		pin_state ? 'B' : 'A',
-		CONFIG_BOARD_MIMX93_EVK_EXP_SEL_INIT_PRIO
-	);
+	LOG_INF("EXP_SEL mux %c with priority %d", pin_state ? 'B' : 'A',
+		CONFIG_BOARD_MIMX93_EVK_EXP_SEL_INIT_PRIO);
 
 	return 0;
 }

boards/nxp/imx93_evk/doc/index.rst

@@ -85,6 +85,35 @@ Serial Port
 This board configuration uses a single serial communication channel with the
 CPU's UART4.
 
+Board MUX Control
+-----------------
+
+This board configuration uses a series of digital multiplexers to switch between
+different board functions. The multiplexers are controlled by a GPIO signal called
+``EXP_SEL`` from onboard GPIO expander ADP5585. It can be configured to select
+function set "A" or "B" by dts configuration if board control module is enabled.
+The following dts node is defined:
+
+.. code-block:: dts
+
+    board_exp_sel: board-exp-sel {
+        compatible = "imx93evk-exp-sel";
+        mux-gpios = <&gpio_exp0 4 GPIO_ACTIVE_HIGH>;
+        mux = "A";
+    };
+
+Following steps are required to configure the ``EXP_SEL`` signal:
+
+1. Enable Kconfig option ``CONFIG_BOARD_MIMX93_EVK_EXP_SEL_INIT``.
+2. Select ``mux="A";`` or ``mux="B";`` in ``&board_exp_sel`` devicetree node.
+
+Kconfig option ``CONFIG_BOARD_MIMX93_EVK_EXP_SEL_INIT`` is enabled if a board
+function that requires configuring the mux is enabled. The MUX option is
+automatically selected if certain board function is enabled, and takes precedence
+over dts config. For instance, if ``CONFIG_CAN`` is enabled, MUX A is selected
+even if ``mux="B";`` is configured in dts, and an warning would be reported in
+the log.
+
 Programming and Debugging
 *************************