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/percpu.h> 14 #include <linux/preempt.h> 15 #include <linux/types.h> 16 17 #ifdef CONFIG_KERNEL_MODE_NEON 18 19 DECLARE_PER_CPU(bool, kernel_neon_busy); 20 21 /* 22 * may_use_simd - whether it is allowable at this time to issue SIMD 23 * instructions or access the SIMD register file 24 * 25 * Callers must not assume that the result remains true beyond the next 26 * preempt_enable() or return from softirq context. 27 */ 28 static __must_check inline bool may_use_simd(void) 29 { 30 /* 31 * The raw_cpu_read() is racy if called with preemption enabled. 32 * This is not a bug: kernel_neon_busy is only set when 33 * preemption is disabled, so we cannot migrate to another CPU 34 * while it is set, nor can we migrate to a CPU where it is set. 35 * So, if we find it clear on some CPU then we're guaranteed to 36 * find it clear on any CPU we could migrate to. 37 * 38 * If we are in between kernel_neon_begin()...kernel_neon_end(), 39 * the flag will be set, but preemption is also disabled, so we 40 * can't migrate to another CPU and spuriously see it become 41 * false. 42 */ 43 return !in_irq() && !in_nmi() && !raw_cpu_read(kernel_neon_busy); 44 } 45 46 #else /* ! CONFIG_KERNEL_MODE_NEON */ 47 48 static __must_check inline bool may_use_simd(void) { 49 return false; 50 } 51 52 #endif /* ! CONFIG_KERNEL_MODE_NEON */ 53 54 #endif 55