boards: particle_boron: Fix init of modem pins

The Boron has a power switch that controls power to a level shifter
for the modem's serial line. Previously, this switch was being enabled
after the modem driver had already started. It is now controlled using
a fixed regulator.

The board initialization was also configuring the V_INT_DETECT pin.
However, this pin is already handled as mdm-vint-gpios in the dts when
the ublox-sara-r4 driver is used. Since it is not used otherwise,
there is no need to configure it in the board init.

Fixes: zephyrproject-rtos#56883
Signed-off-by: Göran Weinholt <goran@weinholt.se>

boards/arm/particle_boron/board.c

@@ -7,7 +7,6 @@
 
 #include <zephyr/init.h>
 #include <zephyr/drivers/gpio.h>
-#include "board.h"
 
 #define ANT_UFLn_GPIO_SPEC	GPIO_DT_SPEC_GET(DT_NODELABEL(sky13351), vctl1_gpios)
 
@@ -29,30 +28,9 @@ static inline void external_antenna(bool on)
 
 static int board_particle_boron_init(void)
 {
-
 	external_antenna(false);
 
-#if defined(CONFIG_MODEM_UBLOX_SARA)
-	const struct device *gpio_dev;
-
-	/* Enable the serial buffer for SARA-R4 modem */
-	gpio_dev = DEVICE_DT_GET(SERIAL_BUFFER_ENABLE_GPIO_NODE);
-	if (!device_is_ready(gpio_dev)) {
-		return -ENODEV;
-	}
-
-	gpio_pin_configure(gpio_dev, V_INT_DETECT_GPIO_PIN,
-			   GPIO_INPUT | V_INT_DETECT_GPIO_FLAGS);
-
-	gpio_pin_configure(gpio_dev, SERIAL_BUFFER_ENABLE_GPIO_PIN,
-			   GPIO_OUTPUT_ACTIVE
-			   | SERIAL_BUFFER_ENABLE_GPIO_FLAGS);
-#endif
-
 	return 0;
 }
 
-/* needs to be done after GPIO driver init, which is at
- * POST_KERNEL:KERNEL_INIT_PRIORITY_DEFAULT.
- */
-SYS_INIT(board_particle_boron_init, POST_KERNEL, 99);
+SYS_INIT(board_particle_boron_init, POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEVICE);

boards/arm/particle_boron/particle_boron.dts

@@ -23,6 +23,14 @@
 		vctl2-gpios = <&gpio0 7 GPIO_ACTIVE_HIGH>;
 	};
 
+	/* Power to the level shifter for uart1 */
+	en_buff_pwr: enable-buff-pwr {
+		compatible = "regulator-fixed";
+		regulator-name = "en_buff_pwr";
+		enable-gpios = <&gpio0 25 GPIO_ACTIVE_LOW>;
+		regulator-boot-on;
+	};
+
 	aliases {
 		watchdog0 = &wdt0;
 	};

boards/arm/particle_boron/particle_boron_defconfig

@@ -24,3 +24,8 @@ CONFIG_UART_CONSOLE=y
 CONFIG_GPIO_AS_PINRESET=y
 
 CONFIG_PINCTRL=y
+
+# Fix the priority to enable the modem line's serial buffer
+# before the modem driver starts (gsm_ppp or ublox-sara-r4).
+CONFIG_REGULATOR=y
+CONFIG_REGULATOR_FIXED_INIT_PRIORITY=41