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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (c) 2020 Western Digital Corporation or its affiliates.
*/
#include <linux/errno.h>
#include <linux/of.h>
#include <linux/string.h>
#include <linux/sched/task_stack.h>
#include <asm/cpu_ops.h>
#include <asm/sbi.h>
#include <asm/smp.h>
const struct cpu_operations cpu_ops_spinwait;
void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data");
void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data");
static void cpu_update_secondary_bootdata(unsigned int cpuid,
struct task_struct *tidle)
{
int hartid = cpuid_to_hartid_map(cpuid);
/*
* The hartid must be less than NR_CPUS to avoid out-of-bound access
* errors for __cpu_spinwait_stack/task_pointer. That is not always possible
* for platforms with discontiguous hartid numbering scheme. That's why
* spinwait booting is not the recommended approach for any platforms
* booting Linux in S-mode and can be disabled in the future.
*/
if (hartid == INVALID_HARTID || hartid >= NR_CPUS)
return;
/* Make sure tidle is updated */
smp_mb();
WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],
task_stack_page(tidle) + THREAD_SIZE);
WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);
}
static int spinwait_cpu_prepare(unsigned int cpuid)
{
if (!cpu_ops_spinwait.cpu_start) {
pr_err("cpu start method not defined for CPU [%d]\n", cpuid);
return -ENODEV;
}
return 0;
}
static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
{
/*
* In this protocol, all cpus boot on their own accord. _start
* selects the first cpu to boot the kernel and causes the remainder
* of the cpus to spin in a loop waiting for their stack pointer to be
* setup by that main cpu. Writing to bootdata
* (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they
* can continue the boot process.
*/
cpu_update_secondary_bootdata(cpuid, tidle);
return 0;
}
const struct cpu_operations cpu_ops_spinwait = {
.name = "spinwait",
.cpu_prepare = spinwait_cpu_prepare,
.cpu_start = spinwait_cpu_start,
};
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