From ea2d9a96b6abe57d72d39a7af24e0120f5df0a8c Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Sun, 19 Mar 2017 17:23:31 +0100
Subject: ARM: 8663/1: wire up HWCAP/HWCAP2 feature bits to the CPU modalias
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.
Since it is non-trivial to transparantly support both HWCAP and HWCAP2
capabilities in the cpu_feature() macro (which allows a module's hwcap
dependency and init routine to be declared using a single invocation of
module_cpu_feature_match()), support only HWCAP2 for now, which covers
the capabilities that are most likely to be useful in this manner.
Module dependencies on HWCAP will need to be declared explicitly via a
MODULE_DEVICE_TABLE(cpu, ...) declaration.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
arch/arm/include/asm/cpufeature.h | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
create mode 100644 arch/arm/include/asm/cpufeature.h
(limited to 'arch/arm/include')
diff --git a/arch/arm/include/asm/cpufeature.h b/arch/arm/include/asm/cpufeature.h
new file mode 100644
index 000000000000..6d425191d01d
--- /dev/null
+++ b/arch/arm/include/asm/cpufeature.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * 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 <linux/log2.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 hardware capability bits have
+ * been distributed over 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 cover those via the cpu_feature()
+ * convenience macro for now (which is used by module_cpu_feature_match()).
+ * However, all capabilities are exposed via the modalias, and can be matched
+ * using an explicit MODULE_DEVICE_TABLE() that uses __hwcap_feature() directly.
+ */
+#define MAX_CPU_FEATURES 64
+#define __hwcap_feature(x) ilog2(HWCAP_ ## x)
+#define __hwcap2_feature(x) (32 + ilog2(HWCAP2_ ## x))
+#define cpu_feature(x) __hwcap2_feature(x)
+
+static inline bool cpu_have_feature(unsigned int num)
+{
+ return num < 32 ? elf_hwcap & BIT(num) : elf_hwcap2 & BIT(num - 32);
+}
+
+#endif
--
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