Re: PPC_FPU, ALTIVEC: enable_kernel_fp, put_vr, get_vr

[Christophe Leroy]

Le 19/04/2021 à 23:39, Randy Dunlap a écrit :
> 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]
>             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 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
>   	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
> @@ -309,6 +310,7 @@ config PHYS_64BIT
>   
>   config ALTIVEC
>   	bool "AltiVec Support"
> +	depends on PPC_FPU

Shouldn't we do it the other way round ? In extenso make ALTIVEC select PPC_FPU and avoid the two 
selects that are above ?

>   	depends on PPC_BOOK3S_32 || PPC_BOOK3S_64 || (PPC_E500MC && PPC64)
>   	help
>   	  This option enables kernel support for the Altivec extensions to the