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 <linux/sched/task_stack.h>
10#include <asm/cpu_ops.h>
11#include <asm/sbi.h>
12#include <asm/smp.h>
13
14#include "head.h"
15
16const struct cpu_operations cpu_ops_spinwait;
17void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data");
18void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data");
19
20static void cpu_update_secondary_bootdata(unsigned int cpuid,
21 struct task_struct *tidle)
22{
23 unsigned long hartid = cpuid_to_hartid_map(cpuid);
24
25 /*
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.
31 */
32 if (hartid == INVALID_HARTID || hartid >= (unsigned long) NR_CPUS)
33 return;
34
35 /* Make sure tidle is updated */
36 smp_mb();
37 WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid], task_pt_regs(tidle));
38 WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
39}
40
41static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
42{
43 /*
44 * In this protocol, all cpus boot on their own accord. _start
45 * selects the first cpu to boot the kernel and causes the remainder
46 * of the cpus to spin in a loop waiting for their stack pointer to be
47 * setup by that main cpu. Writing to bootdata
48 * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they
49 * can continue the boot process.
50 */
51 cpu_update_secondary_bootdata(cpuid, tidle);
52
53 return 0;
54}
55
56const struct cpu_operations cpu_ops_spinwait = {
57 .cpu_start = spinwait_cpu_start,
58};
59

source code of linux/arch/riscv/kernel/cpu_ops_spinwait.c