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