How to represent negative values for device tree property

Hi,

I am working on a thermal driver which needs to be able to read a temperature threshold from a device tree property. The hardware supports thresholds in the range -204.8 to +204.7 C in 0.1 C steps. I have found, as I am sure others have as well, that dtc treats a '-' before an integer in a dtsi file as a syntax error. Therefore, I need some artificial way to represent negative numbers in device tree. Here are the possibilities that I have thought of so far:

1. Use a second integer to specify the sign of the threshold:

     20000 mC --> <0 20000>
    -20000 mC --> <1 20000>
2. Use a string instead of an integer to specify the threshold and
   then convert it to an integer in the driver software:
     20000 mC --> "20000"
    -20000 mC --> "-20000"
3. Use units of millikelvin instead of millicelcius.  0 mC == 273150 mK
     20000 mC --> <293150>
    -20000 mC --> <253150>
4. Use an arbitrary offset e.g. 0 mC == 1000000
     20000 mC --> <1020000>
    -20000 mC --> <980000>
5. Use the unsigned 32-bit representation for 2’s-compliment
   signed 32-bit integer
     20000 mC --> <20000>
    -20000 mC --> <0xffffb1e0> or <4294947296>

Which of these options would you recommend using? Is there any better way to handle negative values that I haven’t listed? What is the best general case solution for specifying negative numbers in device tree?

Thanks,
David

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