arm64/hwcap: Support FEAT_EBF16

The v9.2 feature FEAT_EBF16 provides support for an extended BFloat16 mode.
Allow userspace to discover system support for this feature by adding a
hwcap for it.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220707103632.12745-4-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

Author: broonie

Documentation/arm64/elf_hwcaps.rst

@@ -301,6 +301,10 @@ HWCAP2_WFXT
 
     Functionality implied by ID_AA64ISAR2_EL1.WFXT == 0b0010.
 
+HWCAP2_EBF16
+
+    Functionality implied by ID_AA64ISAR1_EL1.BF16 == 0b0010.
+
 4. Unused AT_HWCAP bits
 -----------------------
 

arch/arm64/include/asm/hwcap.h

@@ -118,6 +118,7 @@
 #define KERNEL_HWCAP_SME_F32F32		__khwcap2_feature(SME_F32F32)
 #define KERNEL_HWCAP_SME_FA64		__khwcap2_feature(SME_FA64)
 #define KERNEL_HWCAP_WFXT		__khwcap2_feature(WFXT)
+#define KERNEL_HWCAP_EBF16		__khwcap2_feature(EBF16)
 
 /*
  * This yields a mask that user programs can use to figure out what

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

@@ -91,5 +91,6 @@
 #define HWCAP2_SME_F32F32	(1 << 29)
 #define HWCAP2_SME_FA64		(1 << 30)
 #define HWCAP2_WFXT		(1UL << 31)
+#define HWCAP2_EBF16		(1UL << 32)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -2641,6 +2641,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_FRINTTS_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_FRINT),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_SB_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_SB),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_BF16_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_BF16),
+	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_BF16_SHIFT, 4, FTR_UNSIGNED, 2, CAP_HWCAP, KERNEL_HWCAP_EBF16),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_DGH_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_DGH),
 	HWCAP_CAP(SYS_ID_AA64ISAR1_EL1, ID_AA64ISAR1_I8MM_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_I8MM),
 	HWCAP_CAP(SYS_ID_AA64MMFR2_EL1, ID_AA64MMFR2_AT_SHIFT, 4, FTR_UNSIGNED, 1, CAP_HWCAP, KERNEL_HWCAP_USCAT),

arch/arm64/kernel/cpuinfo.c

@@ -107,6 +107,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_SME_F32F32]	= "smef32f32",
 	[KERNEL_HWCAP_SME_FA64]		= "smefa64",
 	[KERNEL_HWCAP_WFXT]		= "wfxt",
+	[KERNEL_HWCAP_EBF16]		= "ebf16",
 };
 
 #ifdef CONFIG_COMPAT