drivers: rtc: STM32 rtc scalers #89313

greavesinator85 · 2025-04-30T10:09:54Z

Allow RTC prescalers to be configurable via dts.

Prescalers can now be adjusted to give more accurate RTC readings, up to 30.5us on LSI/LSE

erwango

I have some doubts about the motivation behind this change and if it is actually required.
Please clarify and see comments to make the usage of these new properties fully clear to user.

Also, this compatible is STM32 generic so please remove STM32U5 from the title and provide a more detailled description about the usefulness of this change

dts/bindings/rtc/st,stm32-rtc.yaml

drivers/rtc/rtc_ll_stm32.c

Allow RTC prescalers to be configurable via dts Signed-off-by: Jake Greaves <[email protected]>

greavesinator85 · 2025-05-06T09:30:29Z

I have some doubts about the motivation behind this change and if it is actually required. Please clarify and see comments to make the usage of these new properties fully clear to user.

Also, this compatible is STM32 generic so please remove STM32U5 from the title and provide a more detailled description about the usefulness of this change

Ready for re-review. This was needed to make the most use out of the RTC sub second register, giving our RTC timestamping accuracy of up to 30.5us

erwango

Looks good for this part.

However (and it seems you're bound to hit all the corner cases in our drivers):

There's already a prescaler part of st,stm32-rtc binding inherited from rtc.yaml. No impact from what I could see but worse to be cross-checked
This binding also applies to drivers/counter/counter_ll_stm32_rtc.c driver, which implements these prescalers in a different way and we're not supposed to make properties specific to a driver ("compatible is supposed to describe hardware"). So you'd need to align also counter rtc driver to make use of those (which is a more consequent clean up I'm affraid)

dts/bindings/rtc/st,stm32-rtc.yaml

greavesinator85 · 2025-05-30T13:48:47Z

Looks good for this part.

However (and it seems you're bound to hit all the corner cases in our drivers):

There's already a prescaler part of st,stm32-rtc binding inherited from rtc.yaml. No impact from what I could see but worse to be cross-checked

This binding also applies to drivers/counter/counter_ll_stm32_rtc.c driver, which implements these prescalers in a different way and we're not supposed to make properties specific to a driver ("compatible is supposed to describe hardware"). So you'd need to align also counter rtc driver to make use of those (which is a more consequent clean up I'm affraid)

I cross checked the existing prescaler and I also don't see a conflict.

I've refactored the rtc counter driver to include the new prescaler override options

sonarqubecloud · 2025-06-02T10:39:49Z

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
17.6% Duplication on New Code

See analysis details on SonarQube Cloud

etienne-lms

@greavesinator85, could you move all changes related to coding style into a dedicated commit?
Commit "drivers: counter: STM32 rtc counter" header line should be rephrased IMHO, to something like drivers: counter: stm32: config RTC prescaler from DT.

etienne-lms · 2025-06-03T10:08:43Z

drivers/counter/counter_ll_stm32_rtc.c

+	defined(CONFIG_SOC_SERIES_STM32L0X) || defined(CONFIG_SOC_SERIES_STM32L1X) ||              \
+	defined(CONFIG_SOC_SERIES_STM32L5X) || defined(CONFIG_SOC_SERIES_STM32H7X) ||              \
+	defined(CONFIG_SOC_SERIES_STM32H5X) || defined(CONFIG_SOC_SERIES_STM32WLX)
+#define RTC_EXTI_LINE LL_EXTI_LINE_17


Unrelated change? I would suggest to discard it.

Ditto for changes on tick_t type definition and added space char to #endif directive line.

etienne-lms · 2025-06-03T10:10:18Z

drivers/counter/counter_ll_stm32_rtc.c

 static int rtc_stm32_start(const struct device *dev)
 {
 #if defined(CONFIG_SOC_SERIES_STM32WBAX) || defined(CONFIG_SOC_SERIES_STM32U5X)
 	const struct device *const clk = DEVICE_DT_GET(STM32_CLOCK_CONTROL_NODE);
 	const struct rtc_stm32_config *cfg = dev->config;

 	/* Enable RTC bus clock */
-	if (clock_control_on(clk, (clock_control_subsys_t) &cfg->pclken[0]) != 0) {
+	if (clock_control_on(clk, (clock_control_subsys_t)&cfg->pclken[0]) != 0) {


I would be in favor of such a change. However I think it deserved a specific commit.

Removed formatting changes from this PR

etienne-lms · 2025-06-03T10:19:50Z

dts/bindings/rtc/st,stm32-rtc.yaml

-      when HSE is selected as the source clock.
+      RTC HSE prescaler value. Optional, if not set defaulted in code to:
+      - not used if source clock is LSE/LSI
+      - value calculated based on HSE clock frequency if RTC source clock is HSE


I would suggest another phrasing:

RTC HSE prescaler value. Applies only when RTC source clock is HSE. Optional, defaulting to the value calculated based on HSE clock frequency.

Updated to reflect this

Handle RTC prescaler options inside RTC counter driver Signed-off-by: Jake Greaves <[email protected]>

sonarqubecloud · 2025-07-03T12:33:15Z

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
24.4% Duplication on New Code

See analysis details on SonarQube Cloud

github-actions bot added area: RTC Real Time Clock platform: STM32 ST Micro STM32 labels Apr 30, 2025

github-actions bot requested review from bjarki-andreasen, djiatsaf-st, erwango, FRASTM, gautierg-st, GeorgeCGV, marwaiehm-st and mathieuchopstm April 30, 2025 10:10

github-actions bot assigned erwango Apr 30, 2025

erwango requested changes Apr 30, 2025

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greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch 3 times, most recently from 5e3f372 to 2db263e Compare May 1, 2025 14:16

drivers: rtc: STM32U5XX rtc scalers

d09764a

Allow RTC prescalers to be configurable via dts Signed-off-by: Jake Greaves <[email protected]>

greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch from 2db263e to d09764a Compare May 1, 2025 14:19

greavesinator85 requested a review from erwango May 1, 2025 14:21

greavesinator85 changed the title ~~drivers: rtc: STM32U5XX rtc scalers~~ drivers: rtc: STM32 rtc scalers May 1, 2025

erwango requested changes May 6, 2025

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github-actions bot added the area: Counter label May 30, 2025

github-actions bot requested review from etienne-lms and nordic-krch May 30, 2025 13:43

greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch 2 times, most recently from 85ccb70 to 57d6954 Compare May 30, 2025 14:10

github-actions bot added the area: Samples Samples label May 30, 2025

github-actions bot requested review from kartben and nashif May 30, 2025 14:11

greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch from 57d6954 to 5388d4d Compare May 30, 2025 14:11

greavesinator85 requested a review from erwango May 30, 2025 14:12

greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch 2 times, most recently from cce5cbf to 9a45464 Compare June 2, 2025 10:11

etienne-lms reviewed Jun 3, 2025

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greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch 2 times, most recently from 9284f8e to fe2a86e Compare July 3, 2025 12:05

drivers: counter: stm32: config rtc prescaler from DT

8bf4e52

Handle RTC prescaler options inside RTC counter driver Signed-off-by: Jake Greaves <[email protected]>

greavesinator85 force-pushed the stm32u5-config-rtc-scalers-via-dts branch from fe2a86e to 8bf4e52 Compare July 3, 2025 12:06

mathieuchopstm added this to the v4.3.0 milestone Jul 3, 2025

greavesinator85 requested a review from etienne-lms July 3, 2025 13:08

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drivers: rtc: STM32 rtc scalers #89313

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greavesinator85 commented Apr 30, 2025 •

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