From c0385b24af15020a1e505f2c984db0d7c0d017e1 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 3 Feb 2015 12:39:03 +0000 Subject: arm64: introduce CONFIG_ARM64_LSE_ATOMICS as fallback to ll/sc atomics In order to patch in the new atomic instructions at runtime, we need to generate wrappers around the out-of-line exclusive load/store atomics. This patch adds a new Kconfig option, CONFIG_ARM64_LSE_ATOMICS. which causes our atomic functions to branch to the out-of-line ll/sc implementations. To avoid the register spill overhead of the PCS, the out-of-line functions are compiled with specific compiler flags to force out-of-line save/restore of any registers that are usually caller-saved. Reviewed-by: Catalin Marinas Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'arch/arm64/Kconfig') diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 5372e1e0c11c..8dabffa82ef8 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -618,6 +618,18 @@ config ARM64_PAN The feature is detected at runtime, and will remain as a 'nop' instruction if the cpu does not implement the feature. +config ARM64_LSE_ATOMICS + bool "ARMv8.1 atomic instructions" + help + As part of the Large System Extensions, ARMv8.1 introduces new + atomic instructions that are designed specifically to scale in + very large systems. + + Say Y here to make use of these instructions for the in-kernel + atomic routines. This incurs a small overhead on CPUs that do + not support these instructions and requires the kernel to be + built with binutils >= 2.25. + menuconfig ARMV8_DEPRECATED bool "Emulate deprecated/obsolete ARMv8 instructions" depends on COMPAT -- cgit v1.2.3