Messages in this thread | | | Subject | Re: [PATCH 2/5] arm64: cpufeature: Track unsigned fields | From | "Suzuki K. Poulose" <> | Date | Fri, 20 Nov 2015 13:37:00 +0000 |
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On 19/11/15 18:45, Catalin Marinas wrote: > On Thu, Nov 19, 2015 at 10:03:13AM +0000, Suzuki K. Poulose wrote: >> On 19/11/15 04:57, AKASHI Takahiro wrote:
> a) A precise value (number of breakpoint registers) or a value from > which you derive some precise value. You mentioned these above > > b) Fields defining the presence of a feature (1, 2, 3). These would > always be positive since the absence of such feature would mean a > value of 0 > > c) Fields defining the absence of a feature by setting 0xf. These are > usually fields that were initial RAZ and turned to -1. I don't expect > such field be greater than 0, nor smaller than -1. > > So I think we can treat (a) and (b) as unsigned permanently.
Agreed.
> We could treat (c) as unsigned as well with a value of 0xf though I'm not sure > how it matches your LOWER/HIGHER_SAFE definitions.
I think we should treat (c) as signed, as we never know what could change, given that meaning of (0xf - implies unsupported) < meaning of (0 - supported). Treating them unsigned could break the LOWER/HIGHER_SAFE definitions and makes the safe value selection ugly.
Cheers Suzuki
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