Re: [PATCH v2] powerpc: make ALTIVEC select PPC_FPU

On a kernel config with ALTIVEC=y and PPC_FPU not set/enabled,
there are build errors:

drivers/cpufreq/pmac32-cpufreq.c:262:2: error: implicit declaration of function 'enable_kernel_fp' [-Werror,-Wimplicit-function-declaration]
            enable_kernel_fp();
../arch/powerpc/lib/sstep.c: In function 'do_vec_load':
../arch/powerpc/lib/sstep.c:637:3: error: implicit declaration of function 'put_vr' [-Werror=implicit-function-declaration]
   637 |   put_vr(rn, &u.v);
       |   ^~~~~~
../arch/powerpc/lib/sstep.c: In function 'do_vec_store':
../arch/powerpc/lib/sstep.c:660:3: error: implicit declaration of function 'get_vr'; did you mean 'get_oc'? [-Werror=implicit-function-declaration]
   660 |   get_vr(rn, &u.v);
       |   ^~~~~~

In theory ALTIVEC is independent of PPC_FPU but in practice nobody
is going to build such a machine, so make ALTIVEC require PPC_FPU
by selecting it.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Christophe Leroy <redacted>
Cc: Segher Boessenkool <redacted>
Cc: lkp@intel.com
---
v2: change ALTIVEC depends on PPC_FPU to select (Christophe and Michael)

  arch/powerpc/platforms/86xx/Kconfig    |    1 +
  arch/powerpc/platforms/Kconfig.cputype |    2 ++
  2 files changed, 3 insertions(+)

--- linux-next-20210416.orig/arch/powerpc/platforms/86xx/Kconfig
+++ linux-next-20210416/arch/powerpc/platforms/86xx/Kconfig

@@ -4,6 +4,7 @@ menuconfig PPC_86xx
  	bool "86xx-based boards"
  	depends on PPC_BOOK3S_32
  	select FSL_SOC
+	select PPC_FPU

  	select ALTIVEC
  	help
  	  The Freescale E600 SoCs have 74xx cores.

--- linux-next-20210416.orig/arch/powerpc/platforms/Kconfig.cputype
+++ linux-next-20210416/arch/powerpc/platforms/Kconfig.cputype

@@ -186,6 +186,7 @@ config E300C3_CPU
  config G4_CPU
  	bool "G4 (74xx)"
  	depends on PPC_BOOK3S_32
+	select PPC_FPU

  	select ALTIVEC
  
  endchoice

@@ -310,6 +311,7 @@ config PHYS_64BIT
  config ALTIVEC
  	bool "AltiVec Support"
  	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64 || (PPC_E500MC && PPC64)
+	select PPC_FPU
  	help
  	  This option enables kernel support for the Altivec extensions to the
  	  PowerPC processor. The kernel currently supports saving and restoring