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Re: [PATCH v3 6/7] arm64: Advertise ARM64_HAS_DCPODP cpu feature
- From: Andrew Murray <andrew dot murray at arm dot com>
- To: Dave Martin <Dave dot Martin at arm dot com>
- Cc: Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Szabolcs Nagy <Szabolcs dot Nagy at arm dot com>, linux-arm-kernel at lists dot infradead dot org, Mark Rutland <mark dot rutland at arm dot com>, Phil Blundell <pb at pbcl dot net>, libc-alpha at sourceware dot org, linux-api at vger dot kernel dot org
- Date: Wed, 3 Apr 2019 10:23:42 +0100
- Subject: Re: [PATCH v3 6/7] arm64: Advertise ARM64_HAS_DCPODP cpu feature
- References: <20190401104515.39775-1-andrew.murray@arm.com> <20190401104515.39775-7-andrew.murray@arm.com> <20190402145958.GJ3567@e103592.cambridge.arm.com>
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@arm.com>
> > ---
> > 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
> >