Re: [PATCH v2] powerpc/mm: Add mask of always present MMU features

[Christophe Leroy]

Le 21/10/2020 à 16:25, Aneesh Kumar K.V a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
>
> > Le 12/10/2020 à 17:39, Christophe Leroy a écrit :
> > > On the same principle as commit 773edeadf672 ("powerpc/mm: Add mask
> > > of possible MMU features"), add mask for MMU features that are
> > > always there in order to optimise out dead branches.
> > >
> > > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > > ---
> > > v2: Features must be anded with MMU_FTRS_POSSIBLE instead of ~0, otherwise
> > >       MMU_FTRS_ALWAYS is ~0 when no #ifdef matches.
> >
> > This is still not enough. For BOOK3S/32, MMU_FTRS_POSSIBLE is still too much.
> > We need a #ifdef CONFIG_PPC_BOOK3S_32 with 0.
> >
> > Christophe
> >
> > > ---
> > >    arch/powerpc/include/asm/mmu.h | 25 +++++++++++++++++++++++++
> > >    1 file changed, 25 insertions(+)
> > >
> > > diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
> > > index 255a1837e9f7..64e7e7f7cda9 100644
> > > --- a/arch/powerpc/include/asm/mmu.h
> > > +++ b/arch/powerpc/include/asm/mmu.h
> > > @@ -201,8 +201,30 @@ enum {
> > >    		0,
> > >    };
> > >    
> > > +enum {
> > > +	MMU_FTRS_ALWAYS =
> > > +#ifdef CONFIG_PPC_8xx
> > > +		MMU_FTR_TYPE_8xx &
> > > +#endif
> > > +#ifdef CONFIG_40x
> > > +		MMU_FTR_TYPE_40x &
> > > +#endif
> > > +#ifdef CONFIG_PPC_47x
> > > +		MMU_FTR_TYPE_47x &
> > > +#elif defined(CONFIG_44x)
> > > +		MMU_FTR_TYPE_44x &
> > > +#endif
> > > +#if defined(CONFIG_E200) || defined(CONFIG_E500)
> > > +		MMU_FTR_TYPE_FSL_E &
> > > +#endif
> > > +		MMU_FTRS_POSSIBLE,
> > > +};
>
> Will it be simpler if we make it a #define like below?
>
> #ifdef CONFIG_PPC_8XX
> #define MMU_FTR_ALWAYS  MMU_FTR_TYPE_8XX & MMU_FTR_POSSIBLE
> #endif

Yes you are right, it will be simpler, and consistant with CPU_FTR_ALWAYS which is partly set with 
defines after all.

Christophe

> > > +
> > >    static inline bool early_mmu_has_feature(unsigned long feature)
> > >    {
> > > +	if (MMU_FTRS_ALWAYS & feature)
> > > +		return true;
> > > +
> > >    	return !!(MMU_FTRS_POSSIBLE & cur_cpu_spec->mmu_features & feature);
> > >    }
> > >    
> > > @@ -231,6 +253,9 @@ static __always_inline bool mmu_has_feature(unsigned long feature)
> > >    	}
> > >    #endif
> > >    
> > > +	if (MMU_FTRS_ALWAYS & feature)
> > > +		return true;
> > > +
> > >    	if (!(MMU_FTRS_POSSIBLE & feature))
> > >    		return false;
> > >