linux-kernel - Re: [PATCH v2] powerpc: make ALTIVEC select PPC

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Message-ID: <60ac6ff1-6bfa-d335-ac0e-336fe3e50587@csgroup.eu>
Date:   Wed, 21 Apr 2021 07:19:55 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     kernel test robot <lkp@...el.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org,
        Segher Boessenkool <segher@...nel.crashing.org>
Subject: Re: [PATCH v2] powerpc: make ALTIVEC select PPC_FPU



Le 21/04/2021 à 04:56, Randy Dunlap a écrit :
> 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@...radead.org>
> Reported-by: kernel test robot <lkp@...el.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: Segher Boessenkool <segher@...nel.crashing.org>
> Cc: lkp@...el.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

Now that ALTIVEC selects PPC_FPU by itself, I don't think you need that.

>   	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

Same

>   	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
>