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[059/237] ARM: elf: add new hwcap for identifying atomic ldrd/strd instructions

Message ID 1387000406-29111-60-git-send-email-horms+renesas@verge.net.au (mailing list archive)
State New, archived
Headers show

Commit Message

Simon Horman Dec. 14, 2013, 5:50 a.m. UTC 
From: Will Deacon <will.deacon@arm.com>

CPUs implementing LPAE have atomic ldrd/strd instructions, meaning that
userspace software can avoid having to use the exclusive variants of
these instructions if they wish.

This patch advertises the atomicity of these instructions via the
hwcaps, so userspace can detect this CPU feature.

Reported-by: Vladimir Danushevsky <vladimir.danushevsky@oracle.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit a469abd0f868c902b75532579bf87553dcf1b360)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
---
 arch/arm/include/uapi/asm/hwcap.h | 2 +-
 arch/arm/kernel/setup.c           | 8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)
diff mbox

Patch

diff --git a/arch/arm/include/uapi/asm/hwcap.h b/arch/arm/include/uapi/asm/hwcap.h
index 3688fd1..6d34d08 100644
--- a/arch/arm/include/uapi/asm/hwcap.h
+++ b/arch/arm/include/uapi/asm/hwcap.h
@@ -25,6 +25,6 @@ 
 #define HWCAP_IDIVT	(1 << 18)
 #define HWCAP_VFPD32	(1 << 19)	/* set if VFP has 32 regs (not 16) */
 #define HWCAP_IDIV	(HWCAP_IDIVA | HWCAP_IDIVT)
-
+#define HWCAP_LPAE	(1 << 20)
 
 #endif /* _UAPI__ASMARM_HWCAP_H */
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index b4b1d39..6cc3db4 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -355,7 +355,7 @@  void __init early_print(const char *str, ...)
 
 static void __init cpuid_init_hwcaps(void)
 {
-	unsigned int divide_instrs;
+	unsigned int divide_instrs, vmsa;
 
 	if (cpu_architecture() < CPU_ARCH_ARMv7)
 		return;
@@ -368,6 +368,11 @@  static void __init cpuid_init_hwcaps(void)
 	case 1:
 		elf_hwcap |= HWCAP_IDIVT;
 	}
+
+	/* LPAE implies atomic ldrd/strd instructions */
+	vmsa = (read_cpuid_ext(CPUID_EXT_MMFR0) & 0xf) >> 0;
+	if (vmsa >= 5)
+		elf_hwcap |= HWCAP_LPAE;
 }
 
 static void __init feat_v6_fixup(void)
@@ -872,6 +877,7 @@  static const char *hwcap_str[] = {
 	"vfpv4",
 	"idiva",
 	"idivt",
+	"lpae",
 	NULL
 };