arch: arm: Using ISR_DIRECT_PM with zero-latency-interrupt violation

[ibaz-nordic]

Describe the bug
Calling ISR_DIRECT_PM when using ZLI will lead to kernel API. This violates ZLI requirement

I've tried removing ISR_DIRECT_PM but this gives unstable behavior. Is there another solution?

[mmahadevan108]

cc @carlescufi

[carlescufi]

I think this one is for @gmarull, @andyross and @cvinayak

[carlescufi]

ZLIs in general cannot interact with the kernel at all, so I doubt that you can call ISR_DIRECT_PM at all from a ZLI.

[cvinayak]

There is also this: #32342 which I had asked as part of the PR review rework. Basically, using CONFIG_PM would use cpsid i to disable all interrupts:

zephyr/arch/arm/core/aarch32/isr_wrapper.S

Lines 151 to 169 in 4b91c2d

	#ifdef CONFIG_PM
	/*
	* All interrupts are disabled when handling idle wakeup. For tickless
	* idle, this ensures that the calculation and programming of the
	* device for the next timer deadline is not interrupted. For
	* non-tickless idle, this ensures that the clearing of the kernel idle
	* state is not interrupted. In each case, z_pm_save_idle_exit
	* is called with interrupts disabled.
	*/
	#if defined(CONFIG_CPU_CORTEX_M)
	/*
	* Disable interrupts to prevent nesting while exiting idle state. This
	* is only necessary for the Cortex-M because it is the only ARM
	* architecture variant that automatically enables interrupts when
	* entering an ISR.
	*/
	cpsid i /* PRIMASK = 1 */
	#endif

Basically, I would not use CONFIG_PM if using CONFIG_ZERO_LATENCY_IRQS=y, then

zephyr/include/zephyr/arch/arm/aarch32/irq.h

Lines 143 to 148 in 5b3f800

	#ifdef CONFIG_PM
	extern void _arch_isr_direct_pm(void);
	#define ARCH_ISR_DIRECT_PM() _arch_isr_direct_pm()
	#else
	#define ARCH_ISR_DIRECT_PM() do { } while (false)
	#endif

Zephyr Bluetooth Low Energy Controller does not use ZLI by default due to the reason of ZLI not being truely ZLI with CONFIG_PM=y.