cpu_ops_spinwait.c

 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};