Turns out the secret was getting the address and symbols right in the device tree. I create the following as meson-pcf8563.dts, compiled into meson-pcf8563.dtbo, moved to /boot/dtb/amlogic/overlay, and added pcf8563 to the "overlays" line in armbianEnv.txt.
/dts-v1/;
/ {
compatible = "amlogic,meson-gxbb";
fragment@0 {
target-path = "/aliases";
__overlay__ {
i2cA = "/soc/bus@c1100000/i2c@8500";
};
};
fragment@1 {
target-path = "/soc/bus@c1100000/i2c@8500";
__overlay__ {
#address-cells = <1>;
#size-cells = <0>;
pcf8563: rtc@51 {
compatible = "nxp,pcf8563";
reg = <0x51>;
status = "okay";
};
};
};
};