drivers: lora: sx126x: Support fine-grained STM32WL PA config

Add STM32WL-specific sx126x_set_tx_params function based on the
STM32CubeWL modifications to LoRaMac-node.

Add the "power-amplifier-output" DT property to
"st,stm32wl-subghz-radio" for selecting between the RFO_LP and RFO_HP
output configurations provided by the above mentioned function.

Add the "rfo-lp-max-power" and "rfo-hp-max-power" DT properties for
defining the maximum design power of the respective outputs' matching
networks.

closes #48511

Signed-off-by: Kenneth J. Miller <ken@miller.ec>

drivers/lora/sx126x.c

@@ -359,7 +359,7 @@ void SX126xReset(void)
 void SX126xSetRfTxPower(int8_t power)
 {
 	LOG_DBG("power: %" PRIi8, power);
-	SX126xSetTxParams(power, RADIO_RAMP_40_US);
+	sx126x_set_tx_params(power, RADIO_RAMP_40_US);
 }
 
 void SX126xWaitOnBusy(void)

drivers/lora/sx126x_common.h

@@ -15,6 +15,7 @@
 #include <zephyr/drivers/spi.h>
 
 #include <sx126x/sx126x.h>
+#include <sx126x-board.h>
 
 #if DT_HAS_COMPAT_STATUS_OKAY(semtech_sx1261)
 #define DT_DRV_COMPAT semtech_sx1261
@@ -64,6 +65,8 @@ void sx126x_dio1_irq_enable(struct sx126x_data *dev_data);
 
 void sx126x_dio1_irq_disable(struct sx126x_data *dev_data);
 
+void sx126x_set_tx_params(int8_t power, RadioRampTimes_t ramp_time);
+
 int sx126x_variant_init(const struct device *dev);
 
 #endif /* ZEPHYR_DRIVERS_SX126X_COMMON_H_ */

drivers/lora/sx126x_standalone.c

@@ -61,6 +61,11 @@ static void sx126x_dio1_irq_callback(const struct device *dev,
 	}
 }
 
+void sx126x_set_tx_params(int8_t power, RadioRampTimes_t ramp_time)
+{
+	SX126xSetTxParams(power, ramp_time);
+}
+
 int sx126x_variant_init(const struct device *dev)
 {
 	struct sx126x_data *dev_data = dev->data;

drivers/lora/sx126x_stm32wl.c

@@ -16,6 +16,11 @@
 #include <zephyr/irq.h>
 LOG_MODULE_DECLARE(sx126x, CONFIG_LORA_LOG_LEVEL);
 
+static const enum {
+	RFO_LP,
+	RFO_HP,
+} pa_output = DT_INST_STRING_UPPER_TOKEN(0, power_amplifier_output);
+
 void sx126x_reset(struct sx126x_data *dev_data)
 {
 	LL_RCC_RF_EnableReset();
@@ -45,6 +50,71 @@ void sx126x_dio1_irq_disable(struct sx126x_data *dev_data)
 	irq_disable(DT_INST_IRQN(0));
 }
 
+void sx126x_set_tx_params(int8_t power, RadioRampTimes_t ramp_time)
+{
+	uint8_t buf[2];
+
+	if (pa_output == RFO_LP) {
+		const int8_t max_power = DT_INST_PROP(0, rfo_lp_max_power);
+
+		if (power > max_power) {
+			power = max_power;
+		}
+		if (max_power == 15) {
+			SX126xSetPaConfig(0x07, 0x00, 0x01, 0x01);
+			power = 14 - (max_power - power);
+		} else if (max_power == 10) {
+			SX126xSetPaConfig(0x01, 0x00, 0x01, 0x01);
+			power = 13 - (max_power - power);
+		} else { /* default +14 dBm */
+			SX126xSetPaConfig(0x04, 0x00, 0x01, 0x01);
+			power = 14 - (max_power - power);
+		}
+		if (power < -17) {
+			power = -17;
+		}
+
+		/* PA overcurrent protection limit 60 mA */
+		SX126xWriteRegister(REG_OCP, 0x18);
+	} else { /* RFO_HP */
+		/* Better Resistance of the RFO High Power Tx to Antenna
+		 * Mismatch, see STM32WL Erratasheet
+		 */
+		SX126xWriteRegister(REG_TX_CLAMP_CFG,
+				    SX126xReadRegister(REG_TX_CLAMP_CFG)
+					| (0x0F << 1));
+
+		const int8_t max_power = DT_INST_PROP(0, rfo_hp_max_power);
+
+		if (power > max_power) {
+			power = max_power;
+		}
+		if (max_power == 20) {
+			SX126xSetPaConfig(0x03, 0x05, 0x00, 0x01);
+			power = 22 - (max_power - power);
+		} else if (max_power == 17) {
+			SX126xSetPaConfig(0x02, 0x03, 0x00, 0x01);
+			power = 22 - (max_power - power);
+		} else if (max_power == 14) {
+			SX126xSetPaConfig(0x02, 0x02, 0x00, 0x01);
+			power = 14 - (max_power - power);
+		} else { /* default +22 dBm */
+			SX126xSetPaConfig(0x04, 0x07, 0x00, 0x01);
+			power = 22 - (max_power - power);
+		}
+		if (power < -9) {
+			power = -9;
+		}
+
+		/* PA overcurrent protection limit 140 mA */
+		SX126xWriteRegister(REG_OCP, 0x38);
+	}
+
+	buf[0] = power;
+	buf[1] = (uint8_t)ramp_time;
+	SX126xWriteCommand(RADIO_SET_TXPARAMS, buf, 2);
+}
+
 static void radio_isr(const struct device *dev)
 {
 	struct sx126x_data *dev_data = dev->data;

dts/bindings/lora/st,stm32wl-subghz-radio.yaml

@@ -12,3 +12,45 @@ properties:
     required: true
     description: |
       Position of the "Radio IRQ, Busy" interrupt line.
+
+  power-amplifier-output:
+    type: string
+    required: true
+    description: |
+      Selects between the low- and high-power power amplifier output pin.
+    enum:
+      - "rfo-lp"
+      - "rfo-hp"
+
+  rfo-lp-max-power:
+    type: int
+    default: 14
+    description: |
+      Maximum design power for the board's RFO_LP output matching network.
+
+      The default setting of +14 dBm is a prevalent board configuration;
+      however, for optimal performance, it is advisable to align the value with
+      the board's RF design.
+
+      See ST application note AN5457, chapter 5.1.2 for more information.
+    enum:
+      - 10
+      - 14
+      - 15
+
+  rfo-hp-max-power:
+    type: int
+    default: 22
+    description: |
+      Maximum design power for the board's RFO_HP output matching network.
+
+      The default setting of +22 dBm is a prevalent board configuration;
+      however, for optimal performance, it is advisable to align the value with
+      the board's RF design.
+
+      See ST application note AN5457, chapter 5.1.2 for more information.
+    enum:
+      - 14
+      - 17
+      - 20
+      - 22