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arm64: cpufeature: add HWCAP for FEAT_RPRES

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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: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211210165432.8106-4-joey.gouly@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Joey Gouly 2021-12-10 16:54:32 +00:00 committed by Catalin Marinas
parent 9e45365f14
commit 1175011a7d
6 changed files with 17 additions and 0 deletions
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8
Documentation/arm64/cpu-feature-registers.rst
View File

@ -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
-------------------

4
Documentation/arm64/elf_hwcaps.rst
View File

@ -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
-----------------------

1
arch/arm64/include/asm/hwcap.h
View File

@ -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

1
arch/arm64/include/uapi/asm/hwcap.h
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@ -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 */

2
arch/arm64/kernel/cpufeature.c
View File

@ -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),
{},
};

1
arch/arm64/kernel/cpuinfo.c
View File

@ -96,6 +96,7 @@ static const char *const hwcap_str[] = {
[KERNEL_HWCAP_MTE] = "mte",
[KERNEL_HWCAP_ECV] = "ecv",
[KERNEL_HWCAP_AFP] = "afp",
[KERNEL_HWCAP_RPRES] = "rpres",
};
#ifdef CONFIG_COMPAT