Re: [PATCH] powerpc/features: Remove CPU_FTR_NODSISRALIGN

[Aneesh Kumar K.V]

On 10/13/20 3:45 PM, Michael Ellerman wrote:
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > Le 13/10/2020 à 09:23, Aneesh Kumar K.V a écrit :
> > > Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > >
> > > > CPU_FTR_NODSISRALIGN has not been used since
> > > > commit 31bfdb036f12 ("powerpc: Use instruction emulation
> > > > infrastructure to handle alignment faults")
> > > >
> > > > Remove it.
> > > >
> > > > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> > > > ---
> > > >    arch/powerpc/include/asm/cputable.h | 22 ++++++++++------------
> > > >    arch/powerpc/kernel/dt_cpu_ftrs.c   |  8 --------
> > > >    arch/powerpc/kernel/prom.c          |  2 +-
> > > >    3 files changed, 11 insertions(+), 21 deletions(-)
> > > >
> > > > diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> > > > index 1098863e17ee..c598961d9f15 100644
> > > > --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> > > > +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> > > > @@ -273,13 +273,6 @@ static int __init feat_enable_idle_nap(struct dt_cpu_feature *f)
> > > >    	return 1;
> > > >    }
> > > >    
> > > > -static int __init feat_enable_align_dsisr(struct dt_cpu_feature *f)
> > > > -{
> > > > -	cur_cpu_spec->cpu_features &= ~CPU_FTR_NODSISRALIGN;
> > > > -
> > > > -	return 1;
> > > > -}
> > > > -
> > > >    static int __init feat_enable_idle_stop(struct dt_cpu_feature *f)
> > > >    {
> > > >    	u64 lpcr;
> > > > @@ -641,7 +634,6 @@ static struct dt_cpu_feature_match __initdata
> > > >    	{"tm-suspend-hypervisor-assist", feat_enable, CPU_FTR_P9_TM_HV_ASSIST},
> > > >    	{"tm-suspend-xer-so-bug", feat_enable, CPU_FTR_P9_TM_XER_SO_BUG},
> > > >    	{"idle-nap", feat_enable_idle_nap, 0},
> > > > -	{"alignment-interrupt-dsisr", feat_enable_align_dsisr, 0},
>
> Rather than removing it entirely, I'd rather we left a comment, so that
> it's obvious that we are ignoring that feature on purpose, not because
> we forget about it.
>
> eg:
>
> diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
> index f204ad79b6b5..45cb7e59bd13 100644
> --- a/arch/powerpc/kernel/dt_cpu_ftrs.c
> +++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
> @@ -640,7 +640,7 @@ static struct dt_cpu_feature_match __initdata
>   	{"tm-suspend-hypervisor-assist", feat_enable, CPU_FTR_P9_TM_HV_ASSIST},
>   	{"tm-suspend-xer-so-bug", feat_enable, CPU_FTR_P9_TM_XER_SO_BUG},
>   	{"idle-nap", feat_enable_idle_nap, 0},
> -	{"alignment-interrupt-dsisr", feat_enable_align_dsisr, 0},
> +	// "alignment-interrupt-dsisr" ignored
>   	{"idle-stop", feat_enable_idle_stop, 0},
>   	{"machine-check-power8", feat_enable_mce_power8, 0},
>   	{"performance-monitor-power8", feat_enable_pmu_power8, 0},


why not do it as
static int __init feat_enable_align_dsisr(struct dt_cpu_feature *f)
{
	/* This feature should not be enabled */
#ifdef DEBUG
	WARN(1);
#endif

	return 1;
}


-aneesh