| 1 | // SPDX-License-Identifier: GPL-2.0-only |
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| 2 | /* |
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| 3 | * Copyright (c) 2020 Western Digital Corporation or its affiliates. |
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| 4 | */ |
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| 5 | |
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| 6 | #include <linux/errno.h> |
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| 7 | #include <linux/of.h> |
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| 8 | #include <linux/string.h> |
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| 9 | #include <linux/sched/task_stack.h> |
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| 10 | #include <asm/cpu_ops.h> |
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| 11 | #include <asm/sbi.h> |
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| 12 | #include <asm/smp.h> |
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| 13 | |
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| 14 | #include "head.h" |
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| 15 | |
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| 16 | const struct cpu_operations cpu_ops_spinwait; |
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| 17 | void *__cpu_spinwait_stack_pointer[NR_CPUS] __section(".data" ); |
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| 18 | void *__cpu_spinwait_task_pointer[NR_CPUS] __section(".data" ); |
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| 19 | |
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| 20 | static void cpu_update_secondary_bootdata(unsigned int cpuid, |
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| 21 | struct task_struct *tidle) |
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| 22 | { |
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| 23 | unsigned long hartid = cpuid_to_hartid_map(cpuid); |
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| 24 | |
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| 25 | /* |
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| 26 | * The hartid must be less than NR_CPUS to avoid out-of-bound access |
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| 27 | * errors for __cpu_spinwait_stack/task_pointer. That is not always possible |
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| 28 | * for platforms with discontiguous hartid numbering scheme. That's why |
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| 29 | * spinwait booting is not the recommended approach for any platforms |
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| 30 | * booting Linux in S-mode and can be disabled in the future. |
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| 31 | */ |
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| 32 | if (hartid == INVALID_HARTID || hartid >= (unsigned long) NR_CPUS) |
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| 33 | return; |
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| 34 | |
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| 35 | /* Make sure tidle is updated */ |
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| 36 | smp_mb(); |
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| 37 | WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid], |
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| 38 | task_stack_page(tidle) + THREAD_SIZE); |
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| 39 | WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle); |
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| 40 | } |
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| 41 | |
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| 42 | static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle) |
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| 43 | { |
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| 44 | /* |
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| 45 | * In this protocol, all cpus boot on their own accord. _start |
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| 46 | * selects the first cpu to boot the kernel and causes the remainder |
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| 47 | * of the cpus to spin in a loop waiting for their stack pointer to be |
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| 48 | * setup by that main cpu. Writing to bootdata |
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| 49 | * (i.e __cpu_spinwait_stack_pointer) signals to the spinning cpus that they |
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| 50 | * can continue the boot process. |
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| 51 | */ |
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| 52 | cpu_update_secondary_bootdata(cpuid, tidle); |
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| 53 | |
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| 54 | return 0; |
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| 55 | } |
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| 56 | |
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| 57 | const struct cpu_operations cpu_ops_spinwait = { |
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| 58 | .cpu_start = spinwait_cpu_start, |
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| 59 | }; |
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| 60 | |
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