[PATCH v2 3/3] arm64: cpufeature: add HWCAP for FEAT_RPRES
Joey Gouly
joey.gouly at arm.com
Tue Dec 7 04:42:26 PST 2021
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 at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Jonathan Corbet <corbet at lwn.net>
---
Documentation/arm64/cpu-feature-registers.rst | 8 ++++++++
Documentation/arm64/elf_hwcaps.rst | 4 ++++
arch/arm64/include/asm/hwcap.h | 1 +
arch/arm64/include/uapi/asm/hwcap.h | 1 +
arch/arm64/kernel/cpufeature.c | 2 ++
arch/arm64/kernel/cpuinfo.c | 1 +
6 files changed, 17 insertions(+)
diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst
index 1b19d20c2dbd..749ae970c319 100644
--- a/Documentation/arm64/cpu-feature-registers.rst
+++ b/Documentation/arm64/cpu-feature-registers.rst
@@ -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
-------------------
diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf_hwcaps.rst
index 247728d37911..b72ff17d600a 100644
--- a/Documentation/arm64/elf_hwcaps.rst
+++ b/Documentation/arm64/elf_hwcaps.rst
@@ -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
-----------------------
diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
index 2809df2fdd63..f68fbb207473 100644
--- a/arch/arm64/include/asm/hwcap.h
+++ b/arch/arm64/include/asm/hwcap.h
@@ -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
diff --git a/arch/arm64/include/uapi/asm/hwcap.h b/arch/arm64/include/uapi/asm/hwcap.h
index 180da7396549..f03731847d9d 100644
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/arch/arm64/include/uapi/asm/hwcap.h
@@ -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 */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index c36018310da5..a46ab3b1c4d5 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -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),
{},
};
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index f2f8fe02f39c..591c18a889a5 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -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
--
2.17.1
More information about the linux-arm-kernel
mailing list