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>
16 const struct cpu_operations cpu_ops_spinwait;
17 void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data");
18 void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data");
20 static void cpu_update_secondary_bootdata(unsigned int cpuid,
21 struct task_struct *tidle)
23 unsigned long hartid = cpuid_to_hartid_map(cpuid);
26 * The hartid must be less than NR_CPUS to avoid out-of-bound access
27 * errors for __cpu_spinwait_stack/task_pointer. That is not always possible
28 * for platforms with discontiguous hartid numbering scheme. That's why
29 * spinwait booting is not the recommended approach for any platforms
30 * booting Linux in S-mode and can be disabled in the future.
32 if (hartid == INVALID_HARTID || hartid >= (unsigned long) NR_CPUS)
35 /* Make sure tidle is updated */
37 WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],
38 task_stack_page(tidle) + THREAD_SIZE);
39 WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
42 static int spinwait_cpu_prepare(unsigned int cpuid)
44 if (!cpu_ops_spinwait.cpu_start) {
45 pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
51 static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
54 * In this protocol, all cpus boot on their own accord. _start
55 * selects the first cpu to boot the kernel and causes the remainder
56 * of the cpus to spin in a loop waiting for their stack pointer to be
57 * setup by that main cpu. Writing to bootdata
58 * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they
59 * can continue the boot process.
61 cpu_update_secondary_bootdata(cpuid, tidle);
66 const struct cpu_operations cpu_ops_spinwait = {
68 .cpu_prepare = spinwait_cpu_prepare,
69 .cpu_start = spinwait_cpu_start,