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], task_pt_regs(tidle));
38 WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
39 }
40
41 static 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
56 const struct cpu_operations cpu_ops_spinwait = {
57 .cpu_start = spinwait_cpu_start,
58 };
59
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