Make hym8563 default RTC (RTC0) by kernel

[OleksandrK]

The NanoPi R3S contains a hardware clock (HYM8563) with the possibility to connect a backup battery. However, the current kernel adds this clock as an additional one (RTC1).  

I tried to create a device tree overlay, but it does not work. As I understand it, this is because the default Rockchip clock is not included in the device tree.  

So, if I understand correctly, the only way to make the HYM8563 the default clock is to build the kernel with this option enabled.  

Please consider changing the default kernel options to make the HYM8563 the default RTC. 
If there’s another way to make the HYM8563 the default RTC, please advise.

[laibsch]

39 minutes ago, OleksandrK said:

Please consider changing the default kernel options to make the HYM8563 the default RTC. 

 

How would one do that exactly?

[c0rnelius]

On other platforms we can usually set an alias in the DTS for the rtc. On RK I'm not seeing that as an option, but what we can do is make it so one module loads before the other. In short, we set `CONFIG_RTC_DRV_HYM8563=y` and leave `CONFIG_RTC_DRV_RK808=m`. Which will force a hierarchy in the way things load.

 

Case in point;

patrick@nanopir3s:~$ dmesg | grep rtc
[    4.646223] rtc-hym8563 1-0051: registered as rtc0
[    4.647295] rtc-hym8563 1-0051: setting system clock to 2025-08-25T01:34:16 UTC (1756085656)
[    5.548534] rk808-rtc rk808-rtc.5.auto: registered as rtc1
[    5.605731] rockchip-drm display-subsystem: [drm] Cannot find any crtc or sizes
[    5.605810] rockchip-drm display-subsystem: [drm] Cannot find any crtc or sizes

 

We may also be able to achieve this with a udev rule? I'll do a PR after further testing.