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 
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");
19 
20 static 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],
38 		   task_stack_page(tidle) + THREAD_SIZE);
39 	WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
40 }
41 
42 static int spinwait_cpu_prepare(unsigned int cpuid)
43 {
44 	if (!cpu_ops_spinwait.cpu_start) {
45 		pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
46 		return -ENODEV;
47 	}
48 	return 0;
49 }
50 
51 static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
52 {
53 	/*
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.
60 	 */
61 	cpu_update_secondary_bootdata(cpuid, tidle);
62 
63 	return 0;
64 }
65 
66 const struct cpu_operations cpu_ops_spinwait = {
67 	.name		= "spinwait",
68 	.cpu_prepare	= spinwait_cpu_prepare,
69 	.cpu_start	= spinwait_cpu_start,
70 };
71