arm64/hwcap: Add support for FEAT_CSSC

FEAT_CSSC adds a number of new instructions usable to optimise common short
sequences of instructions, add a hwcap indicating that the feature is
available and can be used by userspace.
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20221017152520.1039165-2-broonie@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

Documentation/arm64/elf_hwcaps.rst

@@ -275,6 +275,9 @@ HWCAP2_EBF16
 HWCAP2_SVE_EBF16
     Functionality implied by ID_AA64ZFR0_EL1.BF16 == 0b0010.
 
+HWCAP2_CSSC
+    Functionality implied by ID_AA64ISAR2_EL1.CSSC == 0b0001.
+
 4. Unused AT_HWCAP bits
 -----------------------
 

arch/arm64/include/asm/hwcap.h

@@ -120,6 +120,7 @@
 #define KERNEL_HWCAP_WFXT		__khwcap2_feature(WFXT)
 #define KERNEL_HWCAP_EBF16		__khwcap2_feature(EBF16)
 #define KERNEL_HWCAP_SVE_EBF16		__khwcap2_feature(SVE_EBF16)
+#define KERNEL_HWCAP_CSSC		__khwcap2_feature(CSSC)
 
 /*
  * This yields a mask that user programs can use to figure out what

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

@@ -93,5 +93,6 @@
 #define HWCAP2_WFXT		(1UL << 31)
 #define HWCAP2_EBF16		(1UL << 32)
 #define HWCAP2_SVE_EBF16	(1UL << 33)
+#define HWCAP2_CSSC		(1UL << 34)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -212,6 +212,7 @@ 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_EL1_CSSC_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_HIGHER_SAFE, ID_AA64ISAR2_EL1_BC_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_PTR_AUTH),
 		       FTR_STRICT, FTR_EXACT, ID_AA64ISAR2_EL1_APA3_SHIFT, 4, 0),
@@ -2815,6 +2816,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 #endif /* CONFIG_ARM64_MTE */
 	HWCAP_CAP(SYS_ID_AA64MMFR0_EL1, ID_AA64MMFR0_EL1_ECV_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_ECV),
 	HWCAP_CAP(SYS_ID_AA64MMFR1_EL1, ID_AA64MMFR1_EL1_AFP_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_AFP),
+	HWCAP_CAP(SYS_ID_AA64ISAR2_EL1, ID_AA64ISAR2_EL1_CSSC_SHIFT, 4, FTR_UNSIGNED, ID_AA64ISAR2_EL1_CSSC_IMP, CAP_HWCAP, KERNEL_HWCAP_CSSC),
 	HWCAP_CAP(SYS_ID_AA64ISAR2_EL1, ID_AA64ISAR2_EL1_RPRES_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_RPRES),
 	HWCAP_CAP(SYS_ID_AA64ISAR2_EL1, ID_AA64ISAR2_EL1_WFxT_SHIFT, 4, FTR_UNSIGNED, ID_AA64ISAR2_EL1_WFxT_IMP, CAP_HWCAP, KERNEL_HWCAP_WFXT),
 #ifdef CONFIG_ARM64_SME

arch/arm64/kernel/cpuinfo.c

@@ -116,6 +116,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_WFXT]		= "wfxt",
 	[KERNEL_HWCAP_EBF16]		= "ebf16",
 	[KERNEL_HWCAP_SVE_EBF16]	= "sveebf16",
+	[KERNEL_HWCAP_CSSC]		= "cssc",
 };
 
 #ifdef CONFIG_COMPAT

arch/arm64/tools/sysreg

@@ -484,7 +484,12 @@ EndEnum
 EndSysreg
 
 Sysreg	ID_AA64ISAR2_EL1	3	0	0	6	2
-Res0	63:28
+Res0	63:56
+Enum	55:52	CSSC
+	0b0000	NI
+	0b0001	IMP
+EndEnum
+Res0	51:28
 Enum	27:24	PAC_frac
 	0b0000	NI
 	0b0001	IMP