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73c132c15d
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>
36 lines
1.2 KiB
C
36 lines
1.2 KiB
C
/*
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* linux/arch/arm/include/asm/neon.h
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*
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* Copyright (C) 2013 Linaro Ltd <ard.biesheuvel@linaro.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <asm/hwcap.h>
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#define cpu_has_neon() (!!(elf_hwcap & HWCAP_NEON))
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#ifdef __ARM_NEON__
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/*
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* If you are affected by the BUILD_BUG below, it probably means that you are
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* using NEON code /and/ calling the kernel_neon_begin() function from the same
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* compilation unit. To prevent issues that may arise from GCC reordering or
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* generating(1) NEON instructions outside of these begin/end functions, the
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* only supported way of using NEON code in the kernel is by isolating it in a
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* separate compilation unit, and calling it from another unit from inside a
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* kernel_neon_begin/kernel_neon_end pair.
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*
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* (1) Current GCC (4.7) might generate NEON instructions at O3 level if
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* -mpfu=neon is set.
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*/
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#define kernel_neon_begin() \
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BUILD_BUG_ON_MSG(1, "kernel_neon_begin() called from NEON code")
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#else
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void kernel_neon_begin(void);
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#endif
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void kernel_neon_end(void);
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