On 4/18/21 10:46 AM, Segher Boessenkool wrote: > 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 :-)
Sure. I'll post them later today. They keep FPU and ALTIVEC as independent (build) features. -- ~Randy
