Commit 1175011a authored by Joey Gouly's avatar Joey Gouly Committed by Catalin Marinas
Browse files

arm64: cpufeature: add HWCAP for FEAT_RPRES 



Add a new HWCAP to detect the Increased precision of Reciprocal Estimate
and Reciprocal Square Root Estimate feature (FEAT_RPRES), introduced in Armv8.7.

Also expose this to userspace in the ID_AA64ISAR2_EL1 feature register.

Signed-off-by: default avatarJoey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Acked-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211210165432.8106-4-joey.gouly@arm.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 9e45365f

Documentation/arm64/cpu-feature-registers.rst

+8 −0
Original line number Diff line number Diff line
@@ -283,6 +283,14 @@ infrastructure: 
     | AFP                          | [47-44] |    y    |

     +------------------------------+---------+---------+



  9) ID_AA64ISAR2_EL1 - Instruction set attribute register 2



     +------------------------------+---------+---------+

     | Name                         |  bits   | visible |

     +------------------------------+---------+---------+

     | RPRES                        | [7-4]   |    y    |

     +------------------------------+---------+---------+





Appendix I: Example

-------------------

Documentation/arm64/elf_hwcaps.rst

+4 −0
Original line number Diff line number Diff line
@@ -255,6 +255,10 @@ HWCAP2_AFP 


    Functionality implied by ID_AA64MFR1_EL1.AFP == 0b0001.



HWCAP2_RPRES



    Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001.



4. Unused AT_HWCAP bits

-----------------------

arch/arm64/include/asm/hwcap.h

+1 −0
Original line number Diff line number Diff line
@@ -107,6 +107,7 @@ 
#define KERNEL_HWCAP_MTE		__khwcap2_feature(MTE)

#define KERNEL_HWCAP_ECV		__khwcap2_feature(ECV)

#define KERNEL_HWCAP_AFP		__khwcap2_feature(AFP)

#define KERNEL_HWCAP_RPRES		__khwcap2_feature(RPRES)



/*

 * This yields a mask that user programs can use to figure out what

arch/arm64/include/uapi/asm/hwcap.h

+1 −0
Original line number Diff line number Diff line
@@ -77,5 +77,6 @@ 
#define HWCAP2_MTE		(1 << 18)

#define HWCAP2_ECV		(1 << 19)

#define HWCAP2_AFP		(1 << 20)

#define HWCAP2_RPRES		(1 << 21)



#endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

+2 −0
Original line number Diff line number Diff line
@@ -226,6 +226,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar1[] = { 
};



static const struct arm64_ftr_bits ftr_id_aa64isar2[] = {

	ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR2_RPRES_SHIFT, 4, 0),

	ARM64_FTR_END,

};
@@ -2487,6 +2488,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = { 
#endif /* CONFIG_ARM64_MTE */

	HWCAP_CAP(SYS_ID_AA64MMFR0_EL1, ID_AA64MMFR0_ECV_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_ECV),

	HWCAP_CAP(SYS_ID_AA64MMFR1_EL1, ID_AA64MMFR1_AFP_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_AFP),

	HWCAP_CAP(SYS_ID_AA64ISAR2_EL1, ID_AA64ISAR2_RPRES_SHIFT, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_RPRES),

	{},

};