如何禁用 A53 上的所有 IRQ？

Question

我有这样的代码希望在 wfi 上停止 cpu:

__asm volatile ( "MSR DAIFSET, #15" );
__asm volatile ( "DSB SY" );
__asm volatile ( "ISB SY" );
__asm volatile ("wfi");
print("never get here\n");

问题是我总是收到日志 "never get here"，为什么会这样？我猜想发生的 irq 是 arch timer PPI。但它不应该被禁用吗？

平台是 el3 中的 cortex-a53。

我将代码更改为：

__asm volatile ( "MSR DAIFSET, #15" );
__asm volatile ( "DSB SY" );
__asm volatile ( "ISB SY" );
while (1) {
    __asm volatile ("wfe");
    print("never get here\n");
}

我没完没了"never get here"，唤醒事件源是什么？

Answer 1

wfi 并不像您想象的那样工作。请参阅 ARMv8 Reference Manual，D1.17.2 部分：

D1.17.2 Wait For Interrupt

[...]
The architecture permits a PE to leave the low-power state for any reason, but requires that it must leave the low-power state on receipt of any architected WFI wake-up event.

---------- Note ----------
Because the architecture permits a PE to leave the low-power state for any reason, it is permissible for a PE to treat WFI as a NOP, but this is not recommended for lowest power operation.
----------------------------

[...]

WFI wake-up events

The following are WFI wake-up events:

Any physical SError interrupt, IRQ interrupt, or FIQ interrupt received by the PE, [...] regardless of the value of the corresponding PSTATE.{A, I, F} mask bit.

[...]

---------- Note ----------

WFI wake-up events are never disabled by EDSCR.INTdis, and are never masked by the PSTATE.{A, I, F} mask bits. If wake-up is invoked by an interrupt that is disabled or masked the interrupt is not taken.

[...]

----------------------------

所以你的中断屏蔽工作正常，只是 wfi 不关心那个，可以简单地作为一个 nop 开始。

与此相反，wfe 似乎旨在强制进入低功耗状态，并且确实遵守中断掩码。我只是浏览了一下，所以可能还有一个警告，但请参阅手册中的 G1.18.1 部分。

如何禁用 A53 上的所有 IRQ？

How to disable all IRQs on A53?

arm64

D1.17.2 Wait For Interrupt