arm64: add FEAT_LRCPC3 HWCAP

FEAT_LRCPC3 adds more instructions to support the Release Consistency model.
Add a HWCAP so that userspace can make decisions about instructions it can use.
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230919162757.2707023-2-joey.gouly@arm.com
[catalin.marinas@arm.com: change the HWCAP number]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Documentation/arch/arm64/elf_hwcaps.rst

@@ -311,6 +311,9 @@ HWCAP2_HBC
 HWCAP2_SVE_B16B16
     Functionality implied by ID_AA64ZFR0_EL1.B16B16 == 0b0001.
 
+HWCAP2_LRCPC3
+    Functionality implied by ID_AA64ISAR1_EL1.LRCPC == 0b0011.
+
 4. Unused AT_HWCAP bits
 -----------------------
 

arch/arm64/include/asm/hwcap.h

@@ -140,6 +140,7 @@
 #define KERNEL_HWCAP_MOPS		__khwcap2_feature(MOPS)
 #define KERNEL_HWCAP_HBC		__khwcap2_feature(HBC)
 #define KERNEL_HWCAP_SVE_B16B16		__khwcap2_feature(SVE_B16B16)
+#define KERNEL_HWCAP_LRCPC3		__khwcap2_feature(LRCPC3)
 
 /*
  * This yields a mask that user programs can use to figure out what

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

@@ -105,5 +105,6 @@
 #define HWCAP2_MOPS		(1UL << 43)
 #define HWCAP2_HBC		(1UL << 44)
 #define HWCAP2_SVE_B16B16	(1UL << 45)
+#define HWCAP2_LRCPC3		(1UL << 46)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -2809,6 +2809,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(ID_AA64ISAR1_EL1, FCMA, IMP, CAP_HWCAP, KERNEL_HWCAP_FCMA),
 	HWCAP_CAP(ID_AA64ISAR1_EL1, LRCPC, IMP, CAP_HWCAP, KERNEL_HWCAP_LRCPC),
 	HWCAP_CAP(ID_AA64ISAR1_EL1, LRCPC, LRCPC2, CAP_HWCAP, KERNEL_HWCAP_ILRCPC),
+	HWCAP_CAP(ID_AA64ISAR1_EL1, LRCPC, LRCPC3, CAP_HWCAP, KERNEL_HWCAP_LRCPC3),
 	HWCAP_CAP(ID_AA64ISAR1_EL1, FRINTTS, IMP, CAP_HWCAP, KERNEL_HWCAP_FRINT),
 	HWCAP_CAP(ID_AA64ISAR1_EL1, SB, IMP, CAP_HWCAP, KERNEL_HWCAP_SB),
 	HWCAP_CAP(ID_AA64ISAR1_EL1, BF16, IMP, CAP_HWCAP, KERNEL_HWCAP_BF16),

arch/arm64/kernel/cpuinfo.c

@@ -128,6 +128,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_MOPS]		= "mops",
 	[KERNEL_HWCAP_HBC]		= "hbc",
 	[KERNEL_HWCAP_SVE_B16B16]	= "sveb16b16",
+	[KERNEL_HWCAP_LRCPC3]		= "lrcpc3",
 };
 
 #ifdef CONFIG_COMPAT

arch/arm64/tools/sysreg

@@ -1309,6 +1309,7 @@ UnsignedEnum	23:20	LRCPC
 	0b0000	NI
 	0b0001	IMP
 	0b0010	LRCPC2
+	0b0011	LRCPC3
 EndEnum
 UnsignedEnum	19:16	FCMA
 	0b0000	NI