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arch: riscv: fix hangup of multicore boot

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This patch fixes hangup of RISC-V multicore boot.
Currently boot sequence uses a riscv_cpu_wake_flag to notify wakeup
request for secondary core(s).

But initial value of riscv_cpu_wake_flag is undefined, so current
mechanism is going to hangup if riscv_cpu_wake_flag and mhartid of
secondary core have the same value.

This is an example situation of this problem:

- hart1: check riscv_cpu_wake_flag (value is 1) and end the loop
- hart1: set riscv_cpu_wake_flag to 0
- hart0: set riscv_cpu_wake_flag to 1
         hart0 expects it will be changed to 0 by hart1 but it
         has never happened

Note:
  - hart0's mhartid is 0, hart1's mhartid is 1
  - hart0 is main, hart1 is secondary in this example

Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
This commit is contained in:
Katsuhiro Suzuki 2023-11-09 13:50:31 +09:00 • committed by Carles Cufí
commit 4ce5f7ebe1
2 changed files with 15 additions and 6 deletions
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14
arch/riscv/core/reset.S
View file

@ -93,16 +93,24 @@ aa_loop:
boot_secondary_core:
#if CONFIG_MP_MAX_NUM_CPUS > 1
la t0, riscv_cpu_wake_flag
li t1, -1
sr t1, 0(t0)
la t0, riscv_cpu_boot_flag
sr zero, 0(t0)
wait_secondary_wake_flag:
la t0, riscv_cpu_wake_flag
lr t0, 0(t0)
bne a0, t0, boot_secondary_core
bne a0, t0, wait_secondary_wake_flag
/* Set up stack */
la t0, riscv_cpu_sp
lr sp, 0(t0)
la t0, riscv_cpu_wake_flag
sr zero, 0(t0)
la t0, riscv_cpu_boot_flag
li t1, 1
sr t1, 0(t0)
j z_riscv_secondary_cpu_init
#else
j loop_unconfigured_cores

7
arch/riscv/core/smp.c
View file

@ -17,6 +17,7 @@ volatile struct {
} riscv_cpu_init[CONFIG_MP_MAX_NUM_CPUS];
volatile uintptr_t riscv_cpu_wake_flag;
volatile uintptr_t riscv_cpu_boot_flag;
volatile void *riscv_cpu_sp;
extern void __start(void);
@ -28,7 +29,7 @@ void arch_start_cpu(int cpu_num, k_thread_stack_t *stack, int sz,
riscv_cpu_init[cpu_num].arg = arg;
riscv_cpu_sp = Z_KERNEL_STACK_BUFFER(stack) + sz;
riscv_cpu_wake_flag = _kernel.cpus[cpu_num].arch.hartid;
riscv_cpu_boot_flag = 0U;
#ifdef CONFIG_PM_CPU_OPS
if (pm_cpu_on(cpu_num, (uintptr_t)&__start)) {
@ -37,8 +38,8 @@ void arch_start_cpu(int cpu_num, k_thread_stack_t *stack, int sz,
}
#endif
while (riscv_cpu_wake_flag != 0U) {
;
while (riscv_cpu_boot_flag == 0U) {
riscv_cpu_wake_flag = _kernel.cpus[cpu_num].arch.hartid;
}
}