linux-kernel - Re: [PATCH 5.10 267/290] powerpc: Fix missing declaration of [en/dis]able_kernel

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Message-ID: <CAMuHMdUqDX8NSGNsw4R=-pEk+nNRsBPBhXD91bq4qy-v1ybcJQ@mail.gmail.com>
Date:   Mon, 15 Mar 2021 15:15:32 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        kernel test robot <lkp@...el.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 5.10 267/290] powerpc: Fix missing declaration of [en/dis]able_kernel_vsx()

On Mon, Mar 15, 2021 at 3:04 PM <gregkh@...uxfoundation.org> wrote:
> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> From: Christophe Leroy <christophe.leroy@...roup.eu>
>
> commit bd73758803c2eedc037c2268b65a19542a832594 upstream.
>
> Add stub instances of enable_kernel_vsx() and disable_kernel_vsx()
> when CONFIG_VSX is not set, to avoid following build failure.

Please note that this is not sufficient, and will just turn the build error
in another, different build error.
Waiting for the subsequent fix to enter v5.12-rc4...
https://lore.kernel.org/lkml/2c123f94-ceae-80c0-90e2-21909795eb76@csgroup.eu/

>
>   CC [M]  drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.o
>   In file included from ./drivers/gpu/drm/amd/amdgpu/../display/dc/dm_services_types.h:29,
>                    from ./drivers/gpu/drm/amd/amdgpu/../display/dc/dm_services.h:37,
>                    from drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c:27:
>   drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c: In function 'dcn_bw_apply_registry_override':
>   ./drivers/gpu/drm/amd/amdgpu/../display/dc/os_types.h:64:3: error: implicit declaration of function 'enable_kernel_vsx'; did you mean 'enable_kernel_fp'? [-Werror=implicit-function-declaration]
>      64 |   enable_kernel_vsx(); \
>         |   ^~~~~~~~~~~~~~~~~
>   drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c:640:2: note: in expansion of macro 'DC_FP_START'
>     640 |  DC_FP_START();
>         |  ^~~~~~~~~~~
>   ./drivers/gpu/drm/amd/amdgpu/../display/dc/os_types.h:75:3: error: implicit declaration of function 'disable_kernel_vsx'; did you mean 'disable_kernel_fp'? [-Werror=implicit-function-declaration]
>      75 |   disable_kernel_vsx(); \
>         |   ^~~~~~~~~~~~~~~~~~
>   drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c:676:2: note: in expansion of macro 'DC_FP_END'
>     676 |  DC_FP_END();
>         |  ^~~~~~~~~
>   cc1: some warnings being treated as errors
>   make[5]: *** [drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.o] Error 1
>
> This works because the caller is checking if VSX is available using
> cpu_has_feature():
>
>   #define DC_FP_START() { \
>         if (cpu_has_feature(CPU_FTR_VSX_COMP)) { \
>                 preempt_disable(); \
>                 enable_kernel_vsx(); \
>         } else if (cpu_has_feature(CPU_FTR_ALTIVEC_COMP)) { \
>                 preempt_disable(); \
>                 enable_kernel_altivec(); \
>         } else if (!cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE)) { \
>                 preempt_disable(); \
>                 enable_kernel_fp(); \
>         } \
>
> When CONFIG_VSX is not selected, cpu_has_feature(CPU_FTR_VSX_COMP)
> constant folds to 'false' so the call to enable_kernel_vsx() is
> discarded and the build succeeds.
>
> Fixes: 16a9dea110a6 ("amdgpu: Enable initial DCN support on POWER")
> Cc: stable@...r.kernel.org # v5.6+
> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> [mpe: Incorporate some discussion comments into the change log]
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> Link: https://lore.kernel.org/r/8d7d285a027e9d21f5ff7f850fa71a2655b0c4af.1615279170.git.christophe.leroy@csgroup.eu
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  arch/powerpc/include/asm/switch_to.h |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> --- a/arch/powerpc/include/asm/switch_to.h
> +++ b/arch/powerpc/include/asm/switch_to.h
> @@ -71,6 +71,16 @@ static inline void disable_kernel_vsx(vo
>  {
>         msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
>  }
> +#else
> +static inline void enable_kernel_vsx(void)
> +{
> +       BUILD_BUG();
> +}
> +
> +static inline void disable_kernel_vsx(void)
> +{
> +       BUILD_BUG();
> +}
>  #endif
>
>  #ifdef CONFIG_SPE

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds