Messages in this thread | | | Subject | Re: [PATCH] powerpc: Fix missing declaration of [en/dis]able_kernel_vsx() | From | Christophe Leroy <> | Date | Tue, 9 Mar 2021 10:57:44 +0100 |
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Le 09/03/2021 à 10:16, Geert Uytterhoeven a écrit : > Hi Christophe, > > On Tue, Mar 9, 2021 at 9:52 AM Christophe Leroy > <christophe.leroy@csgroup.eu> wrote: >> Le 09/03/2021 à 09:45, Geert Uytterhoeven a écrit : >>> On Tue, Mar 9, 2021 at 9:39 AM Christophe Leroy >>> <christophe.leroy@csgroup.eu> wrote: >>>> Add stub instances of enable_kernel_vsx() and disable_kernel_vsx() >>>> when CONFIG_VSX is not set, to avoid following build failure. >>>> >>>> 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 >>>> >>>> Fixes: 16a9dea110a6 ("amdgpu: Enable initial DCN support on POWER") >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> >>> >>> Thanks for your patch! >>> >>>> --- 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(void) >>>> { >>>> 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 >>> >>> I'm wondering how this is any better than the current situation: using >>> BUILD_BUG() will still cause a build failure? >> >> No it won't cause a failure. In drivers/gpu/drm/amd/display/dc/os_types.h you have: >> >> #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. > > IC. So you might as well have an empty (dummy) function instead? >
But with an empty function, you take the risk that one day, someone calls it without checking that CONFIG_VSX is selected. Here if someone does that, build will fail.
Another solution is to declare a non static prototype of it, like __put_user_bad() for instance. In that case, the link will fail.
I prefer the BUILD_BUG() approach as I find it cleaner and more explicit, and also because it breaks the build at compile time, you don't have to wait link time to catch the error.
Christophe
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