tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/*
2 * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
3 *
4 * This program is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 as published
6 * by the Free Software Foundation.
7 */
8
9#ifndef __ASM_SIMD_H
10#define __ASM_SIMD_H
11
12#include <linux/compiler.h>
13#include <linux/irqflags.h>
14#include <linux/percpu.h>
15#include <linux/preempt.h>
16#include <linux/types.h>
17
18#ifdef CONFIG_KERNEL_MODE_NEON
19
20DECLARE_PER_CPU(bool, kernel_neon_busy);
21
22/*
23 * may_use_simd - whether it is allowable at this time to issue SIMD
24 * instructions or access the SIMD register file
25 *
26 * Callers must not assume that the result remains true beyond the next
27 * preempt_enable() or return from softirq context.
28 */
29static __must_check inline bool may_use_simd(void)
30{
31 /*
32 * The raw_cpu_read() is racy if called with preemption enabled.
33 * This is not a bug: kernel_neon_busy is only set when
34 * preemption is disabled, so we cannot migrate to another CPU
35 * while it is set, nor can we migrate to a CPU where it is set.
36 * So, if we find it clear on some CPU then we're guaranteed to
37 * find it clear on any CPU we could migrate to.
38 *
39 * If we are in between kernel_neon_begin()...kernel_neon_end(),
40 * the flag will be set, but preemption is also disabled, so we
41 * can't migrate to another CPU and spuriously see it become
42 * false.
43 */
44 return !in_irq() && !irqs_disabled() && !in_nmi() &&
45 !raw_cpu_read(kernel_neon_busy);
46}
47
48#else /* ! CONFIG_KERNEL_MODE_NEON */
49
50static __must_check inline bool may_use_simd(void) {
51 return false;
52}
53
54#endif /* ! CONFIG_KERNEL_MODE_NEON */
55
56#endif