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 13 const struct cpu_operations cpu_ops_spinwait; 14 15 static 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 24 static 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 39 const struct cpu_operations cpu_ops_spinwait = { 40 .name = "spinwait", 41 .cpu_prepare = spinwait_cpu_prepare, 42 .cpu_start = spinwait_cpu_start, 43 }; 44