linux-kernel - [PATCH v3 1/3] arm64/hwcap: Add hwcap for FEAT

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Message-Id: <20250818-arm64-lsfe-v3-1-af6f4d66eb39@kernel.org>
Date: Mon, 18 Aug 2025 20:21:18 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>, 
 Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
 Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
 Shuah Khan <shuah@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, 
 linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev, 
 linux-kselftest@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: [PATCH v3 1/3] arm64/hwcap: Add hwcap for FEAT_LSFE

FEAT_LSFE (Large System Float Extension), providing atomic floating point
memory operations, is optional from v9.5. This feature adds no new
architectural stare and we have no immediate use for it in the kernel so
simply provide a hwcap for it to support discovery by userspace.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
 Documentation/arch/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 +
 5 files changed, 9 insertions(+)

diff --git a/Documentation/arch/arm64/elf_hwcaps.rst b/Documentation/arch/arm64/elf_hwcaps.rst
index f58ada4d6cb2..a15df4956849 100644
--- a/Documentation/arch/arm64/elf_hwcaps.rst
+++ b/Documentation/arch/arm64/elf_hwcaps.rst
@@ -441,6 +441,10 @@ HWCAP3_MTE_FAR
 HWCAP3_MTE_STORE_ONLY
     Functionality implied by ID_AA64PFR2_EL1.MTESTOREONLY == 0b0001.
 
+HWCAP3_LSFE
+    Functionality implied by ID_AA64ISAR3_EL1.LSFE == 0b0001
+
+
 4. Unused AT_HWCAP bits
 -----------------------
 
diff --git a/arch/arm64/include/asm/hwcap.h b/arch/arm64/include/asm/hwcap.h
index 13f94c8ddfc0..6d567265467c 100644
--- a/arch/arm64/include/asm/hwcap.h
+++ b/arch/arm64/include/asm/hwcap.h
@@ -178,6 +178,7 @@
 #define __khwcap3_feature(x)		(const_ilog2(HWCAP3_ ## x) + 128)
 #define KERNEL_HWCAP_MTE_FAR		__khwcap3_feature(MTE_FAR)
 #define KERNEL_HWCAP_MTE_STORE_ONLY	__khwcap3_feature(MTE_STORE_ONLY)
+#define KERNEL_HWCAP_LSFE		__khwcap3_feature(LSFE)
 
 /*
  * 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 72c78468b806..575564ecdb0b 100644
--- a/arch/arm64/include/uapi/asm/hwcap.h
+++ b/arch/arm64/include/uapi/asm/hwcap.h
@@ -145,5 +145,6 @@
  */
 #define HWCAP3_MTE_FAR		(1UL << 0)
 #define HWCAP3_MTE_STORE_ONLY		(1UL << 1)
+#define HWCAP3_LSFE		(1UL << 2)
 
 #endif /* _UAPI__ASM_HWCAP_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9ad065f15f1d..b1219f14459f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -278,6 +278,7 @@ static const struct arm64_ftr_bits ftr_id_aa64isar2[] = {
 
 static const struct arm64_ftr_bits ftr_id_aa64isar3[] = {
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_FPRCVT_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_LSFE_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64ISAR3_EL1_FAMINMAX_SHIFT, 4, 0),
 	ARM64_FTR_END,
 };
@@ -3252,6 +3253,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(ID_AA64ISAR1_EL1, I8MM, IMP, CAP_HWCAP, KERNEL_HWCAP_I8MM),
 	HWCAP_CAP(ID_AA64ISAR2_EL1, LUT, IMP, CAP_HWCAP, KERNEL_HWCAP_LUT),
 	HWCAP_CAP(ID_AA64ISAR3_EL1, FAMINMAX, IMP, CAP_HWCAP, KERNEL_HWCAP_FAMINMAX),
+	HWCAP_CAP(ID_AA64ISAR3_EL1, LSFE, IMP, CAP_HWCAP, KERNEL_HWCAP_LSFE),
 	HWCAP_CAP(ID_AA64MMFR2_EL1, AT, IMP, CAP_HWCAP, KERNEL_HWCAP_USCAT),
 #ifdef CONFIG_ARM64_SVE
 	HWCAP_CAP(ID_AA64PFR0_EL1, SVE, IMP, CAP_HWCAP, KERNEL_HWCAP_SVE),
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index ba834909a28b..c44e6d94f5de 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -162,6 +162,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_SME_SMOP4]	= "smesmop4",
 	[KERNEL_HWCAP_MTE_FAR]		= "mtefar",
 	[KERNEL_HWCAP_MTE_STORE_ONLY]	= "mtestoreonly",
+	[KERNEL_HWCAP_LSFE]		= "lsfe",
 };
 
 #ifdef CONFIG_COMPAT

-- 
2.39.5