On Sun, Apr 18, 2021 at 06:24:29PM +0200, Christophe Leroy wrote: > Le 17/04/2021 à 22:17, Randy Dunlap a écrit : > >Should the code + Kconfigs/Makefiles handle that kind of > >kernel config or should ALTIVEC always mean PPC_FPU as well? > > As far as I understand, Altivec is completely independant of FPU in Theory.
And, as far as the hardware is concerned, in practice as well. > So it should be possible to use Altivec without using FPU. Yup. > However, until recently, it was not possible to de-activate FPU support on > book3s/32. I made it possible in order to reduce unneccessary processing on > processors like the 832x that has no FPU. The processor has to implement FP to be compliant to any version of PowerPC, as far as I know? So that is all done by emulation, including all the registers? Wow painful. > As far as I can see in cputable.h/.c, 832x is the only book3s/32 without > FPU, and it doesn't have ALTIVEC either. 602 doesn't have double-precision hardware, also no 64-bit FP registers. But that CPU was never any widely used :-) > So we can in the future ensure that Altivec can be used without FPU > support, but for the time being I think it is OK to force selection of FPU > when selecting ALTIVEC in order to avoid build failures. It is useful to allow MSR[VEC,FP]=1,0 but yeah there are no CPUs that have VMX (aka AltiVec) but that do not have FP. I don't see how making that artificial dependency buys anything, but maybe it does? > >I have patches to fix the build errors with the config as > >reported but I don't know if that's the right thing to do... Neither do we, we cannot see those patches :-) Segher