linux-stable/arch/arm/include/asm/neon.h
Ard Biesheuvel 73c132c15d 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>
2013-07-08 22:08:51 +01:00

36 lines
1.2 KiB
C

/*
* 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);