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authorArd Biesheuvel <ard.biesheuvel@linaro.org>2013-05-16 11:41:48 +0200
committerArd Biesheuvel <ard.biesheuvel@linaro.org>2013-07-08 22:08:51 +0100
commit73c132c15da504789b924871e2491479a18e4f6a (patch)
treee5aab4cb0d9263419677a4aa9aea392ffad76053 /arch/arm/include/asm/neon.h
parentab3da15643469ab2d206dee3d9cfa4194ba77f25 (diff)
downloadlinux-73c132c15da504789b924871e2491479a18e4f6a.tar.bz2
ARM: add support for kernel mode NEON
In order to safely support the use of NEON instructions in kernel mode, some precautions need to be taken: - the userland context that may be present in the registers (even if the NEON/VFP is currently disabled) must be stored under the correct task (which may not be 'current' in the UP case), - to avoid having to keep track of additional vfpstates for the kernel side, disallow the use of NEON in interrupt context and run with preemption disabled, - after use, re-enable preemption and re-enable the lazy restore machinery by disabling the NEON/VFP unit. This patch adds the functions kernel_neon_begin() and kernel_neon_end() which take care of the above. It also adds the Kconfig symbol KERNEL_MODE_NEON to enable it. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Acked-by: Nicolas Pitre <nico@linaro.org>
Diffstat (limited to 'arch/arm/include/asm/neon.h')
-rw-r--r--arch/arm/include/asm/neon.h36
1 files changed, 36 insertions, 0 deletions
diff --git a/arch/arm/include/asm/neon.h b/arch/arm/include/asm/neon.h
new file mode 100644
index 000000000000..8f730fe70093
--- /dev/null
+++ b/arch/arm/include/asm/neon.h
@@ -0,0 +1,36 @@
+/*
+ * linux/arch/arm/include/asm/neon.h
+ *
+ * Copyright (C) 2013 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.
+ */
+
+#include <asm/hwcap.h>
+
+#define cpu_has_neon() (!!(elf_hwcap & HWCAP_NEON))
+
+#ifdef __ARM_NEON__
+
+/*
+ * If you are affected by the BUILD_BUG below, it probably means that you are
+ * using NEON code /and/ calling the kernel_neon_begin() function from the same
+ * compilation unit. To prevent issues that may arise from GCC reordering or
+ * generating(1) NEON instructions outside of these begin/end functions, the
+ * only supported way of using NEON code in the kernel is by isolating it in a
+ * separate compilation unit, and calling it from another unit from inside a
+ * kernel_neon_begin/kernel_neon_end pair.
+ *
+ * (1) Current GCC (4.7) might generate NEON instructions at O3 level if
+ * -mpfu=neon is set.
+ */
+
+#define kernel_neon_begin() \
+ BUILD_BUG_ON_MSG(1, "kernel_neon_begin() called from NEON code")
+
+#else
+void kernel_neon_begin(void);
+#endif
+void kernel_neon_end(void);