1 // SPDX-License-Identifier: GPL-2.0-only
3 * Copyright (c) 2020 Western Digital Corporation or its affiliates.
6 #include <linux/errno.h>
8 #include <linux/string.h>
9 #include <linux/sched/task_stack.h>
10 #include <asm/cpu_ops.h>
14 const struct cpu_operations cpu_ops_spinwait;
15 void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data");
16 void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data");
18 static void cpu_update_secondary_bootdata(unsigned int cpuid,
19 struct task_struct *tidle)
21 int hartid = cpuid_to_hartid_map(cpuid);
24 * The hartid must be less than NR_CPUS to avoid out-of-bound access
25 * errors for __cpu_spinwait_stack/task_pointer. That is not always possible
26 * for platforms with discontiguous hartid numbering scheme. That's why
27 * spinwait booting is not the recommended approach for any platforms
28 * booting Linux in S-mode and can be disabled in the future.
30 if (hartid == INVALID_HARTID || hartid >= NR_CPUS)
33 /* Make sure tidle is updated */
35 WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],
36 task_stack_page(tidle) + THREAD_SIZE);
37 WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
40 static int spinwait_cpu_prepare(unsigned int cpuid)
42 if (!cpu_ops_spinwait.cpu_start) {
43 pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
49 static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
52 * In this protocol, all cpus boot on their own accord. _start
53 * selects the first cpu to boot the kernel and causes the remainder
54 * of the cpus to spin in a loop waiting for their stack pointer to be
55 * setup by that main cpu. Writing to bootdata
56 * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they
57 * can continue the boot process.
59 cpu_update_secondary_bootdata(cpuid, tidle);
64 const struct cpu_operations cpu_ops_spinwait = {
66 .cpu_prepare = spinwait_cpu_prepare,
67 .cpu_start = spinwait_cpu_start,