1// SPDX-License-Identifier: GPL-2.0-only 2/* 3 * Copyright (c) 2020 Western Digital Corporation or its affiliates. 4 */ 5 6#include <linux/errno.h> 7#include <linux/of.h> 8#include <linux/string.h> 9#include <asm/cpu_ops.h> 10#include <asm/sbi.h> 11#include <asm/smp.h> 12 13const struct cpu_operations cpu_ops_spinwait; 14 15static int spinwait_cpu_prepare(unsigned int cpuid) 16{ 17 if (!cpu_ops_spinwait.cpu_start) { 18 pr_err("cpu start method not defined for CPU [%d]\n", cpuid); 19 return -ENODEV; 20 } 21 return 0; 22} 23 24static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle) 25{ 26 /* 27 * In this protocol, all cpus boot on their own accord. _start 28 * selects the first cpu to boot the kernel and causes the remainder 29 * of the cpus to spin in a loop waiting for their stack pointer to be 30 * setup by that main cpu. Writing to bootdata 31 * (i.e __cpu_up_stack_pointer) signals to the spinning cpus that they 32 * can continue the boot process. 33 */ 34 cpu_update_secondary_bootdata(cpuid, tidle); 35 36 return 0; 37} 38 39const struct cpu_operations cpu_ops_spinwait = { 40 .name = "spinwait", 41 .cpu_prepare = spinwait_cpu_prepare, 42 .cpu_start = spinwait_cpu_start, 43}; 44