On 04/02/2013 12:29 AM, David Gibson wrote: > On Mon, Apr 01, 2013 at 05:24:19PM -0700, David Collins wrote: >> On 04/01/2013 03:00 PM, Stephen Warren wrote: >>> On 04/01/2013 03:08 PM, David Collins wrote: >>>> 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: >>> >>> Doesn't the very latest dtc, which contains integer expression >>> support, allow unary -? I thought that code had been imported >>> into the kernel (goes and checks) yes it has. What's the error >>> you're seeing; over/underflow or syntax? >>> >>> That said, DT cells are supposed to be u32 not s32, so perhaps >>> this isn't unexpected. > > That's.. sort of true, but misleading. As far as the dtb format > is concerned, properties are just a bag of bytes. Individual > device bindings define how software should interpret those bytes. > > The dtc data "types" are really just convenient ways to enter > various sorts of commonly used bytestrings. Some of the dtc code > treats cells as u32 because that works for its purposes (and in > particular avoids some nasty C standard gotchas where signed > overflows may have undefined results), but there's no reason you > can't treat it as an s32. On dtc versions recent enough to have > arithmetic, unary minus and subtractive overflow will use 2's > complement, as you'd expect. OK, perhaps I was extrapolating too far from the fact that all the DT-related code in the kernel (just happens to) only read integers as u32. It sounds like it'd be fine to add e.g. of_property_read_s32() alongside the existing of_property_read_u32() then. I imagine that would be quite useful. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
