stm32_rtc: Prescaler config failed

Hi all,

I'm developing a custom board based on STM32MP153 SoC, and I need to use the internal RTC. I also need to output its 32.768kHz reference clock from I8 pin.

As stated at https://wiki.st.com/stm32mpu/wiki/RTC_device_tree_configuration, into the Linux dts I enabled the internal RTC using this node:

&rtc {
 st,lsco = <RTC_OUT2_RMP>;
 pinctrl-0 = <&rtc_out2_rmp_pins_a>;
 pinctrl-names = "default";
 status = "okay";
};

but at the boot I get this log message:

stm32_rtc 5c004000.rtc: Can't enter in init mode. Prescaler config failed.
stm32_rtc: probe of 5c004000.rtc failed with error -110

The driver is not loaded, thus I don't have the 32.768kHz clock on I8 pin.

Could you help me to figure out what I'm doing wrong?

Thanks in advance, regards

Mauro

[PatrickF]

Hi,

I'm not dts specialist, maybe check that RTC settings are present, e.g. https://github.com/STMicroelectronics/linux/blob/v4.19-stm32mp/Documentation/devicetree/bindings/rtc/st,stm32-rtc.txt

Regards.

Hi PatrickF,

thank you for your answer. All the required settings listed in bindings are present, they are in the stm32mp157c.dtsi include file that is included by my .dts:

In stm32mp157c.dtsi:

rtc: rtc@5c004000 {
			compatible = "st,stm32mp1-rtc";
			reg = <0x5c004000 0x400>;
			clocks = <&rcc RTCAPB>, <&rcc RTC>;
			clock-names = "pclk", "rtc_ck";
			interrupts-extended = <&intc GIC_SPI 3 IRQ_TYPE_LEVEL_HIGH>,
					 <&exti 19 1>;
			status = "disabled";
		};

In my .dts:

/dts-v1/;
 
#include "stm32mp157c.dtsi"
#include "stm32mp157caa-pinctrl.dtsi"
#include "stm32mp157c-m4-srm.dtsi"
#include <dt-bindings/input/input.h>
#include <dt-bindings/rtc/rtc-stm32.h>
 
....
 
 
&rtc {
	st,lsco = <RTC_OUT2_RMP>;
	pinctrl-0 = <&rtc_out2_rmp_pins_a>;
	pinctrl-names = "default";
	status = "okay";
};

Thank you, regards

For everyone facing similar problems, I found that the error was due to the external LSE oscillator, that did not work correctly.

Regards