Wire up the generic support for exposing CPU feature bits via the
modalias in /sys/device/system/cpu. This allows udev to automatically
load modules for things like crypto algorithms that are implemented
using optional instructions.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/cpufeature.h | 32 ++++++++++++++++++++
2 files changed, 33 insertions(+)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b5d529fdffab..1a0c6a486a9c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -21,6 +21,7 @@ config ARM
select GENERIC_ALLOCATOR
select GENERIC_ATOMIC64 if (CPU_V7M || CPU_V6 || !CPU_32v6K || !AEABI)
select GENERIC_CLOCKEVENTS_BROADCAST if SMP
+ select GENERIC_CPU_AUTOPROBE
select GENERIC_EARLY_IOREMAP
select GENERIC_IDLE_POLL_SETUP
select GENERIC_IRQ_PROBE
diff --git a/arch/arm/include/asm/cpufeature.h b/arch/arm/include/asm/cpufeature.h
new file mode 100644
index 000000000000..19c3dddd901a
--- /dev/null
+++ b/arch/arm/include/asm/cpufeature.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2016 Linaro Ltd. <ard.biesheuvel@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __ASM_CPUFEATURE_H
+#define __ASM_CPUFEATURE_H
+
+#include <asm/hwcap.h>
+
+/*
+ * Due to the fact that ELF_HWCAP is a 32-bit type on ARM, and given the number
+ * of optional CPU features it defines, ARM's CPU capability bits have been
+ * divided across separate elf_hwcap and elf_hwcap2 variables, each of which
+ * covers a subset of the available CPU features.
+ *
+ * Currently, only a few of those are suitable for automatic module loading
+ * (which is the primary use case of this facility) and those happen to be all
+ * covered by HWCAP2. So let's only expose those via the CPU modalias for now.
+ */
+#define MAX_CPU_FEATURES (8 * sizeof(elf_hwcap2))
+#define cpu_feature(x) ilog2(HWCAP2_ ## x)
+
+static inline bool cpu_have_feature(unsigned int num)
+{
+ return elf_hwcap2 & (1UL << num);
+}
+
+#endif
--
2.7.4
--
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