Re: PPC_FPU, ALTIVEC: enable_kernel_fp, put_vr, get_vr

From: Randy Dunlap
Date: Mon Apr 19 2021 - 17:39:59 EST

On 4/19/21 6:16 AM, Michael Ellerman wrote:
> Randy Dunlap <rdunlap@xxxxxxxxxxxxx> writes:

>> Sure. I'll post them later today.
>> They keep FPU and ALTIVEC as independent (build) features.
> Those patches look OK.
> But I don't think it makes sense to support that configuration, FPU=n
> ALTVEC=y. No one is ever going to make a CPU like that. We have enough
> testing surface due to configuration options, without adding artificial
> combinations that no one is ever going to use.
> IMHO :)
> So I'd rather we just make ALTIVEC depend on FPU.

That's rather simple. See below.
I'm doing a bunch of randconfig builds with it now.

From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Subject: [PATCH] powerpc: make ALTIVEC depend 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]
../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 depending on PPC_FPU.

Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
Cc: lkp@xxxxxxxxx
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
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

@@ -309,6 +310,7 @@ config PHYS_64BIT

config ALTIVEC
bool "AltiVec Support"
+ depends on PPC_FPU
depends on PPC_BOOK3S_32 || PPC_BOOK3S_64 || (PPC_E500MC && PPC64)
This option enables kernel support for the Altivec extensions to the