nct7802 mode selection for RTD1,2,3 via device tree?

[Oskar Senft <osk@google.com>]

Hi everyone

We're successfully using the nct7802 driver on a TYAN S7106 mainboard
connected to an Aspeed AST2500 BMC running OpenBMC. However, on this
board the NCT7802Y has 3 thermistors connected. For that to work, we
reconfigured the "Mode Selection Register" (0x22) to have RTD1_MD,
RTD2_MD and RTD3_MD set as 0x2 (Thermistor mode). So far we simply had
a one line patch in our internal kernel repo, but we'd like to
upstream it and make it configurable.

We explicitly reference the nct7802 in our device tree. Example:

&i2c0 {
    status = "okay";

    /* Hardware monitor with temperature sensors */
    nct7802@28 {
        compatible = "nuvoton,nct7802";
        reg = <0x28>;
    };
};

Note that the DTS validator complains about not knowing about
"nuvoton,nct7802". Is that because the driver doesn't specify a
MODULE_DEVICE_TABLE of type "struct of_device_id"? I'd be happy to fix
that, too!

Anyway, I was wondering if there would be a nice way to set the
configuration for RTD1,2,3 from the device tree. I'll be happy to make
the necessary changes (there are plenty of examples), but I wanted to
check with the community and maintainers before going down any such
road.

Thanks
Oskar.