arm64/sve: Report FEAT_SVE_B16B16 to userspace

SVE 2.1 introduced a new feature FEAT_SVE_B16B16 which adds instructions
supporting the BFloat16 floating point format. Report this to userspace
through the ID registers and hwcap.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230915-arm64-zfr-b16b16-el0-v1-1-f9aba807bdb5@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: broonie

Documentation/arch/arm64/cpu-feature-registers.rst

@@ -268,6 +268,8 @@ infrastructure:
      +------------------------------+---------+---------+
      | SHA3                         | [35-32] |    y    |
      +------------------------------+---------+---------+
+     | B16B16                       | [27-24] |    y    |
+     +------------------------------+---------+---------+
      | BF16                         | [23-20] |    y    |
      +------------------------------+---------+---------+
      | BitPerm                      | [19-16] |    y    |

Documentation/arch/arm64/elf_hwcaps.rst

@@ -308,6 +308,9 @@ HWCAP2_MOPS
 HWCAP2_HBC
     Functionality implied by ID_AA64ISAR2_EL1.BC == 0b0001.
 
+HWCAP2_SVE_B16B16
+    Functionality implied by ID_AA64ZFR0_EL1.B16B16 == 0b0001.
+
 4. Unused AT_HWCAP bits
 -----------------------
 

arch/arm64/include/asm/hwcap.h

@@ -139,6 +139,7 @@
 #define KERNEL_HWCAP_SME_F16F16		__khwcap2_feature(SME_F16F16)
 #define KERNEL_HWCAP_MOPS		__khwcap2_feature(MOPS)
 #define KERNEL_HWCAP_HBC		__khwcap2_feature(HBC)
+#define KERNEL_HWCAP_SVE_B16B16		__khwcap2_feature(SVE_B16B16)
 
 /*
  * This yields a mask that user programs can use to figure out what

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

@@ -104,5 +104,6 @@
 #define HWCAP2_SME_F16F16	(1UL << 42)
 #define HWCAP2_MOPS		(1UL << 43)
 #define HWCAP2_HBC		(1UL << 44)
+#define HWCAP2_SVE_B16B16	(1UL << 45)
 
 #endif /* _UAPI__ASM_HWCAP_H */

arch/arm64/kernel/cpufeature.c

@@ -278,6 +278,8 @@ static const struct arm64_ftr_bits ftr_id_aa64zfr0[] = {
 		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_EL1_SM4_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
 		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_EL1_SHA3_SHIFT, 4, 0),
+	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
+		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_EL1_B16B16_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
 		       FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ZFR0_EL1_BF16_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE_IF_IS_ENABLED(CONFIG_ARM64_SVE),
@@ -2821,6 +2823,7 @@ static const struct arm64_cpu_capabilities arm64_elf_hwcaps[] = {
 	HWCAP_CAP(ID_AA64ZFR0_EL1, AES, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEAES),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, AES, PMULL128, CAP_HWCAP, KERNEL_HWCAP_SVEPMULL),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, BitPerm, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEBITPERM),
+	HWCAP_CAP(ID_AA64ZFR0_EL1, B16B16, IMP, CAP_HWCAP, KERNEL_HWCAP_SVE_B16B16),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, BF16, IMP, CAP_HWCAP, KERNEL_HWCAP_SVEBF16),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, BF16, EBF16, CAP_HWCAP, KERNEL_HWCAP_SVE_EBF16),
 	HWCAP_CAP(ID_AA64ZFR0_EL1, SHA3, IMP, CAP_HWCAP, KERNEL_HWCAP_SVESHA3),

arch/arm64/kernel/cpuinfo.c

@@ -127,6 +127,7 @@ static const char *const hwcap_str[] = {
 	[KERNEL_HWCAP_SME_F16F16]	= "smef16f16",
 	[KERNEL_HWCAP_MOPS]		= "mops",
 	[KERNEL_HWCAP_HBC]		= "hbc",
+	[KERNEL_HWCAP_SVE_B16B16]	= "sveb16b16",
 };
 
 #ifdef CONFIG_COMPAT

arch/arm64/tools/sysreg

@@ -1026,7 +1026,11 @@ UnsignedEnum	35:32	SHA3
 	0b0000	NI
 	0b0001	IMP
 EndEnum
-Res0	31:24
+Res0	31:28
+UnsignedEnum	27:24	B16B16
+	0b0000	NI
+	0b0001	IMP
+EndEnum
 UnsignedEnum	23:20	BF16
 	0b0000	NI
 	0b0001	IMP