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 const struct cpu_operations cpu_ops_spinwait; 15 void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data"); 16 void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data"); 17 18 static void cpu_update_secondary_bootdata(unsigned int cpuid, 19 struct task_struct *tidle) 20 { 21 int hartid = cpuid_to_hartid_map(cpuid); 22 23 /* 24 * The hartid must be less than NR_CPUS to avoid out-of-bound access 25 * errors for __cpu_spinwait_stack/task_pointer. That is not always possible 26 * for platforms with discontiguous hartid numbering scheme. That's why 27 * spinwait booting is not the recommended approach for any platforms 28 * booting Linux in S-mode and can be disabled in the future. 29 */ 30 if (hartid == INVALID_HARTID || hartid >= NR_CPUS) 31 return; 32 33 /* Make sure tidle is updated */ 34 smp_mb(); 35 WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid], 36 task_stack_page(tidle) + THREAD_SIZE); 37 WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle); 38 } 39 40 static int spinwait_cpu_prepare(unsigned int cpuid) 41 { 42 if (!cpu_ops_spinwait.cpu_start) { 43 pr_err("cpu start method not defined for CPU [%d]\n", cpuid); 44 return -ENODEV; 45 } 46 return 0; 47 } 48 49 static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle) 50 { 51 /* 52 * In this protocol, all cpus boot on their own accord. _start 53 * selects the first cpu to boot the kernel and causes the remainder 54 * of the cpus to spin in a loop waiting for their stack pointer to be 55 * setup by that main cpu. Writing to bootdata 56 * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they 57 * can continue the boot process. 58 */ 59 cpu_update_secondary_bootdata(cpuid, tidle); 60 61 return 0; 62 } 63 64 const struct cpu_operations cpu_ops_spinwait = { 65 .name = "spinwait", 66 .cpu_prepare = spinwait_cpu_prepare, 67 .cpu_start = spinwait_cpu_start, 68 }; 69