From 579401fb8e5f33dda461d872bf5a711072662d59 Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Mon, 1 Oct 2018 13:46:37 +0100 Subject: [PATCH] xen/arm: cpufeature: Add helper to check constant caps Some capababilities are set right during boot and will never change afterwards. At the moment, the function cpu_have_caps will check whether the cap is enabled from the memory. It is possible to avoid the load from the memory by using an ALTERNATIVE. With that the check is just reduced to 1 instruction. Signed-off-by: Julien Grall Reviewed-by: Stefano Stabellini --- xen/include/asm-arm/cpufeature.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h index 3de6b54301..c6cbc2ec84 100644 --- a/xen/include/asm-arm/cpufeature.h +++ b/xen/include/asm-arm/cpufeature.h @@ -63,6 +63,18 @@ static inline bool cpus_have_cap(unsigned int num) return test_bit(num, cpu_hwcaps); } +/* System capability check for constant cap */ +#define cpus_have_const_cap(num) ({ \ + bool __ret; \ + \ + asm volatile (ALTERNATIVE("mov %0, #0", \ + "mov %0, #1", \ + num) \ + : "=r" (__ret)); \ + \ + unlikely(__ret); \ + }) + static inline void cpus_set_cap(unsigned int num) { if (num >= ARM_NCAPS) -- 2.30.2