[Question] Is little endian supported on all the platforms?
mpe at ellerman.id.au
Tue Sep 1 11:39:33 AEST 2015
On Mon, 2015-08-31 at 19:56 +0800, Boqun Feng wrote:
> On Mon, Aug 31, 2015 at 09:19:26PM +1000, Michael Ellerman wrote:
> > On Mon, 2015-08-31 at 15:53 +0800, Boqun Feng wrote:
> > > On Mon, Aug 31, 2015 at 04:52:38PM +1000, Benjamin Herrenschmidt wrote:
> > > > On Mon, 2015-08-31 at 14:44 +0800, Boqun Feng wrote:
> > > > > Hi all,
> > > > >
> > > > > I hit a strange build error on v4.2, when I try to build a LE kernel
> > > > > with a slightly modification of the ppc64_defconfig. What I did is just
> > > > > make ppc64_defconfig and make menuconfig to set CPU_LITTLE_ENDIAN=y, and
> > > > > then build the kernel.
> > > > >
> > > > > I did a little research myself, and found out the error is because of
> > > > > trying to build a LE kernel with CONFIG_PPC_PS3=y. So a simple way to
> > > > > reproduce is:
> > > >
> > > > First, LE isn't supported on PS/3 :-) It's only supported on POWER8
> > > > machines (and *some* P7 machines and only when running as KVM guest).
> > >
> > > Got it, thank you ;-)
> > >
> > > So should we modify Kconfigs of all the platform to reflect this?
> > Yes. Maybe something like this?
> > diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> > index c140e94..c359f72 100644
> > --- a/arch/powerpc/platforms/Kconfig.cputype
> > +++ b/arch/powerpc/platforms/Kconfig.cputype
> > @@ -415,9 +415,13 @@ config VDSO32
> > big endian. That is because the only little endian configuration we
> > support is ppc64le which is 64-bit only.
> > +config CHOOSE_ENDIAN
> > + bool
> > +
> > choice
> > prompt "Endianness selection"
> > default CPU_BIG_ENDIAN
> > + depends on CHOOSE_ENDIAN
> > help
> > This option selects whether a big endian or little endian kernel will
> > be built.
> > diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
> > index 604190c..32d5661 100644
> > --- a/arch/powerpc/platforms/powernv/Kconfig
> > +++ b/arch/powerpc/platforms/powernv/Kconfig
> > @@ -18,6 +18,7 @@ config PPC_POWERNV
> > select CPU_FREQ_GOV_ONDEMAND
> > select CPU_FREQ_GOV_CONSERVATIVE
> > select PPC_DOORBELL
> > + select CHOOSE_ENDIAN
> IIUC, we can actually set PPC_POWERNV=y and PPC_PS3=y at the same time,
> So this can't prevent PPC_PS3 && CPU_LITTLE_ENDIAN from being true.
So that's probably not a good solution.
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