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