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Linux/arch/arm64/include/asm/simd.h

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  1 /* SPDX-License-Identifier: GPL-2.0-only */
  2 /*
  3  * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
  4  */
  5 
  6 #ifndef __ASM_SIMD_H
  7 #define __ASM_SIMD_H
  8 
  9 #include <linux/compiler.h>
 10 #include <linux/irqflags.h>
 11 #include <linux/percpu.h>
 12 #include <linux/preempt.h>
 13 #include <linux/types.h>
 14 
 15 DECLARE_PER_CPU(bool, fpsimd_context_busy);
 16 
 17 #ifdef CONFIG_KERNEL_MODE_NEON
 18 
 19 /*
 20  * may_use_simd - whether it is allowable at this time to issue SIMD
 21  *                instructions or access the SIMD register file
 22  *
 23  * Callers must not assume that the result remains true beyond the next
 24  * preempt_enable() or return from softirq context.
 25  */
 26 static __must_check inline bool may_use_simd(void)
 27 {
 28         /*
 29          * We must make sure that the SVE has been initialized properly
 30          * before using the SIMD in kernel.
 31          * fpsimd_context_busy is only set while preemption is disabled,
 32          * and is clear whenever preemption is enabled. Since
 33          * this_cpu_read() is atomic w.r.t. preemption, fpsimd_context_busy
 34          * cannot change under our feet -- if it's set we cannot be
 35          * migrated, and if it's clear we cannot be migrated to a CPU
 36          * where it is set.
 37          */
 38         return !WARN_ON(!system_capabilities_finalized()) &&
 39                system_supports_fpsimd() &&
 40                !in_irq() && !irqs_disabled() && !in_nmi() &&
 41                !this_cpu_read(fpsimd_context_busy);
 42 }
 43 
 44 #else /* ! CONFIG_KERNEL_MODE_NEON */
 45 
 46 static __must_check inline bool may_use_simd(void) {
 47         return false;
 48 }
 49 
 50 #endif /* ! CONFIG_KERNEL_MODE_NEON */
 51 
 52 #endif
 53 

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