Segher Boessenkool <seg...@kernel.crashing.org> writes: > 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 :-)
Yeah for those of us who don't see bits cascading in our sleep I think the popcount is easier to understand ;) cheers
