DS1307 on rpi4B

Hello all,

I'm trying connect DS1307 on rpi4B (8M). I'm not sure how much I can rely
on the description in
https://github.com/raspberrypi/firmware/tree/master/boot/overlays because I
don't know the difference between linux boot loader and FreeBSD one.

I want to connect DS1307 on GPIO12/13 pin as i2c5 so I assumed i2c-rtc
could be used so that I added one line in config.txt like below.

dtoverlay=i2c-rtc,ds1307,i2c5,addr=0x68

iic1 is detected at boot but it can't talk to DS1307.

# dmesg | egrep iic\|ds1307
iichb0: <BCM2708/2835 BSC controller> mem 0x7e804000-0x7e804fff irq 27 on
simplebus0
iichb1: <BCM2708/2835 BSC controller> mem 0x7e205a00-0x7e205bff irq 52 on
simplebus0
iicbus0: <OFW I2C bus> on iichb0
iic0: <I2C generic I/O> on iicbus0
iicbus1: <OFW I2C bus> on iichb1
iic1: <I2C generic I/O> on iicbus1
ds13070: <Dallas DS1307> at addr 0xd0 on iicbus1
ds13070: is_dev_time_valid: cannot read from RTC: 35
ds13070: WARNING: RTC clock stopped, check the battery.
ds13070: registered as a time-of-day clock, resolution 1.000000s
ds13070: ds1307_gettime: cannot read from RTC: 35
ds13070: ds1307_settime: cannot write to RTC: 35

The command "i2c -s -v -f /dev/iic1" can't detect anything at all. The pin
function doesn't seem to be correct.
# sysctl -a dev.gpio.0.pin|grep 1[23]
dev.gpio.0.pin.13.function: input
dev.gpio.0.pin.12.function: input

If I set alt5 on these pins by sysctl and change pin configuration by
gpioctl to enable internal pullup, iic1 works fine.
---
for p in 12 13
do
  sysctl dev.gpio.0.pin.$p.function=alt5
  gpioctl -c $p PU
done
i2c -s -v -f /dev/iic1
/root/src/ds1307 -r -a 0x68 -f /dev/iic1
---

I'm not familiar with dts stuff but I wrote overlay dts like this.
/dts-v1/;
/plugin/;
/  {

        compatible = "raspberrypi,4-model-b", "brcm,bcm2711";
        fragment@0 {
                        target = <&i2c5>;
                        __overlay__ {
                        brcm,pins = <12 13>;
                        brcm,function = <2>;
                        brcm,pull = <2 2>;
                        status = "okay";
                };

        };
};
However this doesn't work at all. How can I configure gpio12/13 for i2c5?

Best regards,
furaisanjin