[PATCH v3 3/3] arm64: cpufeature: add HWCAP for FEAT_RPRES

[Joey Gouly]

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