You could test RTC in Linux.
Please compile Kernel with RTC driver enabled.

In addition, enable RTC device driver similar as the following.
root@localhost:~# zcat /proc/config.gz | grep CONFIG_RTC_DRV_PCF85363
CONFIG_RTC_DRV_PCF85363=y
In dts, configure RTC similar as the following.
&i2c0 {
status = "okay";
... ...
rtc@68 {
compatible = "pericom,pt7c4338";
reg = <0x68>;
};
rtc@51 {
compatible = "nxp,pcf85263";
reg = <0x51>;
};
};
In Linux OS on the target board.
root@localhost:~# hwclock -s
date
root@localhost:~# date
Mon Jul 1 14:02:39 UTC 2030