drivers: rtc: Add support for RTC for stm32n6 series

Add rtc node on stm32n6 DT.
Enable backup domain access for RTC clock configuration on stm32n6

Signed-off-by: Basile GRUNER <basile.gruner@smile.fr>

Author: basilegrunersmile

boards/st/nucleo_n657x0_q/nucleo_n657x0_q_common.dtsi

@@ -53,6 +53,7 @@
 		led0 = &green_led;
 		led1 = &blue_led;
 		led2 = &red_led;
+		rtc = &rtc;
 		sw0 = &user_button;
 		watchdog0 = &iwdg;
 	};
@@ -96,6 +97,10 @@
 	status = "okay";
 };
 
+&clk_lse {
+	status = "okay";
+};
+
 &pll1 {
 	clocks = <&clk_hse>;
 	div-m = <3>;
@@ -343,3 +348,9 @@ csi_capture_port: &pipe_main {};
 &iwdg {
 	status = "okay";
 };
+
+&rtc {
+	clocks = <&rcc STM32_CLOCK(APB4, 16)>,
+		 <&rcc STM32_SRC_LSE RTC_SEL(1)>;
+	status = "okay";
+};

boards/st/stm32n6570_dk/stm32n6570_dk_common.dtsi

@@ -30,6 +30,7 @@
 	aliases {
 		led0 = &green_led_1;
 		led1 = &red_led_2;
+		rtc = &rtc;
 		sw0 = &user_button;
 		watchdog0 = &iwdg;
 	};
@@ -126,6 +127,10 @@
 	status = "okay";
 };
 
+&clk_lse {
+	status = "okay";
+};
+
 &pll1 {
 	clocks = <&clk_hse>;
 	div-m = <3>;
@@ -577,3 +582,9 @@ zephyr_jpegenc: &jpeg {
 &crc {
 	status = "okay";
 };
+
+&rtc {
+	clocks = <&rcc STM32_CLOCK(APB4, 16)>,
+		 <&rcc STM32_SRC_LSE RTC_SEL(1)>;
+	status = "okay";
+};

drivers/rtc/rtc_stm32.c

@@ -485,6 +485,11 @@ static int rtc_stm32_init(const struct device *dev)
 
 	int err = 0;
 
+#if defined(CONFIG_SOC_SERIES_STM32N6X)
+	/* STM32N6 needs backup domain access before configuring RTC clock */
+	stm32_backup_domain_enable_access();
+#endif /* CONFIG_SOC_SERIES_STM32N6X */
+
 	/* Enable RTC bus clock */
 	if (clock_control_on(clk, (clock_control_subsys_t)&cfg->pclken[0]) != 0) {
 		LOG_ERR("clock op failed\n");
@@ -521,7 +526,9 @@ static int rtc_stm32_init(const struct device *dev)
 	}
 #endif /* CONFIG_SOC_SERIES_STM32WB0X */
 
+#if !defined(CONFIG_SOC_SERIES_STM32N6X)
 	stm32_backup_domain_enable_access();
+#endif /* !CONFIG_SOC_SERIES_STM32N6X */
 
 #if DT_INST_CLOCKS_CELL_BY_IDX(0, 1, bus) == STM32_SRC_HSE
 	/* Must be configured before selecting the RTC clock source */

dts/arm/st/n6/stm32n6.dtsi

@@ -1351,6 +1351,15 @@
 				};
 			};
 
+			rtc: rtc@6004000 {
+				compatible = "st,stm32-rtc";
+				reg = <0x46004000 0x400>;
+				interrupts = <16 0>;
+				clocks = <&rcc STM32_CLOCK(APB4, 16)>;
+				alarms-count = <2>;
+				status = "disabled";
+			};
+
 			xspim: xspim@802b400 {
 				compatible = "st,stm32-xspim";
 				reg = <0x802b400 0x400>;