ARM: 9273/1: Add hwcap for Speculation Barrier(SB)

Speculation Barrier(FEAT_SB) is a feature present in AArch32 state for
Armv8 and is represented by ISAR6.SB identification register.

This feature denotes the presence of SB instruction and hence adding a
hwcap will enable the userspace to check it before trying to use this
instruction.

This commit adds the ID feature bit detection, and uses elf_hwcap2
accordingly.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

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

@@ -43,5 +43,6 @@
 #define HWCAP2_SHA1	(1 << 2)
 #define HWCAP2_SHA2	(1 << 3)
 #define HWCAP2_CRC32	(1 << 4)
+#define HWCAP2_SB	(1 << 5)
 
 #endif /* _UAPI__ASMARM_HWCAP_H */

arch/arm/kernel/setup.c

@@ -450,6 +450,7 @@ static void __init cpuid_init_hwcaps(void)
 {
 	int block;
 	u32 isar5;
+	u32 isar6;
 
 	if (cpu_architecture() < CPU_ARCH_ARMv7)
 		return;
@@ -485,6 +486,12 @@ static void __init cpuid_init_hwcaps(void)
 	block = cpuid_feature_extract_field(isar5, 16);
 	if (block >= 1)
 		elf_hwcap2 |= HWCAP2_CRC32;
+
+	/* Check for Speculation barrier instruction */
+	isar6 = read_cpuid_ext(CPUID_EXT_ISAR6);
+	block = cpuid_feature_extract_field(isar6, 12);
+	if (block >= 1)
+		elf_hwcap2 |= HWCAP2_SB;
 }
 
 static void __init elf_hwcap_fixup(void)
@@ -1264,6 +1271,7 @@ static const char *hwcap2_str[] = {
 	"sha1",
 	"sha2",
 	"crc32",
+	"sb",
 	NULL
 };