Re: [PATCH v3 6/7] arm64: Advertise ARM64_HAS_DCPODP cpu feature

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On Tue, Apr 02, 2019 at 03:59:58PM +0100, Dave Martin wrote:
> On Mon, Apr 01, 2019 at 11:45:14AM +0100, Andrew Murray wrote:
> > Advertise ARM64_HAS_DCPOP when both DC CVAP and DC CVADP are supported.
> 
> Do you mean ARM64_HAS_DCPODP?

Yes I did - good catch.

> 
> And do we need this?  This capability flag doesn't currently appear to
> be used for anything (which makes me wonder whether it _should_ be wired
> up to something in the kernel).
> 
> Do we expect the kernel to do something special with this in the future?
> 
> OTOH, we get a nice printk when the feature is detected, and the code
> size cost is insignificant.  So, if there's a reasonable expectation that
> we will use it someday, I don't see a big problem with having it.

Yes it's not currently used, so I'm happy to drop this patch if people prefer
that - however it does complement the existing DCPOP cap which is present.

Thanks,

Andrew Murray

> 
> Cheers
> ---Dave
> 
> > 
> > Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
> > ---
> >  arch/arm64/include/asm/cpucaps.h | 3 ++-
> >  arch/arm64/kernel/cpufeature.c   | 9 +++++++++
> >  2 files changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> > index f6a76e43f39e..defdc67d9ab4 100644
> > --- a/arch/arm64/include/asm/cpucaps.h
> > +++ b/arch/arm64/include/asm/cpucaps.h
> > @@ -61,7 +61,8 @@
> >  #define ARM64_HAS_GENERIC_AUTH_ARCH		40
> >  #define ARM64_HAS_GENERIC_AUTH_IMP_DEF		41
> >  #define ARM64_HAS_IRQ_PRIO_MASKING		42
> > +#define ARM64_HAS_DCPODP			43
> >  
> > -#define ARM64_NCAPS				43
> > +#define ARM64_NCAPS				44
> >  
> >  #endif /* __ASM_CPUCAPS_H */
> > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> > index 5e27d2dbe45e..c74b25895c43 100644
> > --- a/arch/arm64/kernel/cpufeature.c
> > +++ b/arch/arm64/kernel/cpufeature.c
> > @@ -1339,6 +1339,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> >  		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
> >  		.min_field_value = 1,
> >  	},
> > +	{
> > +		.desc = "Data cache clean to Point of Deep Persistence",
> > +		.capability = ARM64_HAS_DCPODP,
> > +		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
> > +		.matches = has_cpuid_feature,
> > +		.sys_reg = SYS_ID_AA64ISAR1_EL1,
> > +		.field_pos = ID_AA64ISAR1_DPB_SHIFT,
> > +		.min_field_value = 2,
> > +	},
> >  #endif
> >  #ifdef CONFIG_ARM64_SVE
> >  	{
> > -- 
> > 2.21.0
> > 



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