57 lines
1.6 KiB
C
57 lines
1.6 KiB
C
/*
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* Copyright (C) 2017 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 it
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* under the terms of the GNU General Public License version 2 as published
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* by the Free Software Foundation.
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*/
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#ifndef __ASM_SIMD_H
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#define __ASM_SIMD_H
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#include <linux/compiler.h>
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#include <linux/irqflags.h>
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#include <linux/percpu.h>
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#include <linux/preempt.h>
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#include <linux/types.h>
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#ifdef CONFIG_KERNEL_MODE_NEON
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DECLARE_PER_CPU(bool, kernel_neon_busy);
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/*
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* may_use_simd - whether it is allowable at this time to issue SIMD
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* instructions or access the SIMD register file
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*
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* Callers must not assume that the result remains true beyond the next
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* preempt_enable() or return from softirq context.
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*/
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static __must_check inline bool may_use_simd(void)
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{
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/*
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* The raw_cpu_read() is racy if called with preemption enabled.
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* This is not a bug: kernel_neon_busy is only set when
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* preemption is disabled, so we cannot migrate to another CPU
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* while it is set, nor can we migrate to a CPU where it is set.
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* So, if we find it clear on some CPU then we're guaranteed to
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* find it clear on any CPU we could migrate to.
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*
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* If we are in between kernel_neon_begin()...kernel_neon_end(),
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* the flag will be set, but preemption is also disabled, so we
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* can't migrate to another CPU and spuriously see it become
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* false.
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*/
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return !in_irq() && !irqs_disabled() && !in_nmi() &&
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!raw_cpu_read(kernel_neon_busy);
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}
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#else /* ! CONFIG_KERNEL_MODE_NEON */
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static __must_check inline bool may_use_simd(void) {
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return false;
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}
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#endif /* ! CONFIG_KERNEL_MODE_NEON */
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#endif
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