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/*
* 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_SIMD_H
#define __ASM_SIMD_H
#include <linux/compiler.h>
#include <linux/irqflags.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/types.h>
#ifdef CONFIG_KERNEL_MODE_NEON
DECLARE_PER_CPU(bool, kernel_neon_busy);
/*
* may_use_simd - whether it is allowable at this time to issue SIMD
* instructions or access the SIMD register file
*
* Callers must not assume that the result remains true beyond the next
* preempt_enable() or return from softirq context.
*/
static __must_check inline bool may_use_simd(void)
{
/*
* The raw_cpu_read() is racy if called with preemption enabled.
* This is not a bug: kernel_neon_busy is only set when
* preemption is disabled, so we cannot migrate to another CPU
* while it is set, nor can we migrate to a CPU where it is set.
* So, if we find it clear on some CPU then we're guaranteed to
* find it clear on any CPU we could migrate to.
*
* If we are in between kernel_neon_begin()...kernel_neon_end(),
* the flag will be set, but preemption is also disabled, so we
* can't migrate to another CPU and spuriously see it become
* false.
*/
return !in_irq() && !irqs_disabled() && !in_nmi() &&
!raw_cpu_read(kernel_neon_busy);
}
#else /* ! CONFIG_KERNEL_MODE_NEON */
static __must_check inline bool may_use_simd(void) {
return false;
}
#endif /* ! CONFIG_KERNEL_MODE_NEON */
#endif
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