| Message ID | 1437154221-5736-2-git-send-email-james.morse@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Jul 17, 2015 at 06:30:16PM +0100, James Morse wrote: > Copied from arch/arm/include/asm/cputype.h, this function does the > shifting and sign extension necessary when accessing cpu feature fields. > > Signed-off-by: James Morse <james.morse@arm.com> > Suggested-by: Russell King <linux@arm.linux.org.uk> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will.deacon@arm.com> > --- > arch/arm64/include/asm/cpufeature.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > index c1044218a63a..56c843918504 100644 > --- a/arch/arm64/include/asm/cpufeature.h > +++ b/arch/arm64/include/asm/cpufeature.h > @@ -70,6 +70,19 @@ static inline void cpus_set_cap(unsigned int num) > __set_bit(num, cpu_hwcaps); > } > > +static inline int __attribute_const__ cpuid_feature_extract_field(u64 features, > + int field) > +{ > + int feature = (features >> field) & 15; > + > + /* feature registers are signed values */ > + if (feature > 8) > + feature -= 16; > + > + return feature; > +} It may generate better code like, especially when field is a constant: return (s64)(feature << (64 - 4 - field)) >> (64 - 4); (in asm I think we could do it with a single instruction but the above shouldn't be that bad either).
On Mon, Jul 20, 2015 at 12:32:37PM +0100, Catalin Marinas wrote: > On Fri, Jul 17, 2015 at 06:30:16PM +0100, James Morse wrote: > > Copied from arch/arm/include/asm/cputype.h, this function does the > > shifting and sign extension necessary when accessing cpu feature fields. > > > > Signed-off-by: James Morse <james.morse@arm.com> > > Suggested-by: Russell King <linux@arm.linux.org.uk> > > Cc: Catalin Marinas <catalin.marinas@arm.com> > > Cc: Will Deacon <will.deacon@arm.com> > > --- > > arch/arm64/include/asm/cpufeature.h | 13 +++++++++++++ > > 1 file changed, 13 insertions(+) > > > > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h > > index c1044218a63a..56c843918504 100644 > > --- a/arch/arm64/include/asm/cpufeature.h > > +++ b/arch/arm64/include/asm/cpufeature.h > > @@ -70,6 +70,19 @@ static inline void cpus_set_cap(unsigned int num) > > __set_bit(num, cpu_hwcaps); > > } > > > > +static inline int __attribute_const__ cpuid_feature_extract_field(u64 features, > > + int field) > > +{ > > + int feature = (features >> field) & 15; > > + > > + /* feature registers are signed values */ > > + if (feature > 8) > > + feature -= 16; > > + > > + return feature; > > +} > > It may generate better code like, especially when field is a constant: > > return (s64)(feature << (64 - 4 - field)) >> (64 - 4); > > (in asm I think we could do it with a single instruction but the above > shouldn't be that bad either). gcc managed to impress me ;). It detects the left-right shifts and inlines "sbfx xn, xn, #field, #4" when the field is a constant.
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index c1044218a63a..56c843918504 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -70,6 +70,19 @@ static inline void cpus_set_cap(unsigned int num) __set_bit(num, cpu_hwcaps); } +static inline int __attribute_const__ cpuid_feature_extract_field(u64 features, + int field) +{ + int feature = (features >> field) & 15; + + /* feature registers are signed values */ + if (feature > 8) + feature -= 16; + + return feature; +} + + void check_cpu_capabilities(const struct arm64_cpu_capabilities *caps, const char *info); void check_local_cpu_errata(void);
Copied from arch/arm/include/asm/cputype.h, this function does the shifting and sign extension necessary when accessing cpu feature fields. Signed-off-by: James Morse <james.morse@arm.com> Suggested-by: Russell King <linux@arm.linux.org.uk> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> --- arch/arm64/include/asm/cpufeature.h | 13 +++++++++++++ 1 file changed, 13 insertions(+)