On Thu, May 09, 2024 at 10:12:48PM +1000, Michael Ellerman wrote:
> cpu_has_feature()/mmu_has_feature() are only able to check a single
> feature at a time, but there is no enforcement of that.
>
> In fact, as fixed in the previous commit, there was code that was
> passing multiple values to cpu_has_feature().
>
> So add a check that only a single feature is passed using popcount.
>
> Note that the test allows 0 or 1 bits to be set, because some code
> relies on cpu_has_feature(0) being false, the check with
> CPU_FTRS_POSSIBLE ensures that. See for example CPU_FTR_PPC_LE.
This btw is exactly
BUILD_BUG_ON(feature & (feature - 1));
but the popcount is more readable :-)
Segher
