stm32_rtc: Prescaler config failed

[MSK]

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.

[MSK]

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

[MSK · Accepted solution]

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

Regards