Suspend to RAM feature not taking care of all cortex-m hw reinitializations

[asm5878]

Describe the bug

When suspend to ram feature is enabled cortex-m not all the registers
are re-initialized (or restored).

In my specific case I am using a nucleo_stm32wba55cg platform.
So a cortx-m33 architecture.
Without these reinitializations and according specific cortex-m related configurations enabled,
we can face hard fault/usage faults.

I have simply used or redefined specific kernel functions at power.c level for my specific soc, such as:
z_arm_floating_point_init
z_arm_exc_setup
z_arm_fault_init
z_arm_clear_faults
z_arm_configure_static_mpu_regions

inside pm_s2ram.S we clearly have all is strictly required for cpu regs and special regs.

To Reproduce

My pm configuration is the following:
CONFIG_PM=y
CONFIG_PM_DEVICE=y
CONFIG_PM_DEVICE_RUNTIME=y
CONFIG_PM_DEVICE_SYSTEM_MANAGED=y
CONFIG_PM_S2RAM=y

Indeed we should enable and use features not properly reconfigured after a wake up form stdby

Expected behavior

suspend to ram should work independently from enabled cortex-m features
Impact

Suspend to RAM is not completely transparent from an application point of view

Logs and console output

Environment (please complete the following information):

• windows
• 0.16.5-1
• 4.1

Additional context

Thanks,
@asm5878

[dkalowsk]

@asm5878 reading through this issue, it sounds that you may have a solution. Any chance for a PR?

[asm5878]

Hi @dkalowsk, I have just understood the kernel init functions should be recalled after a stdby restart and applied them in my power.c context.
However I think I am not close to organize a clear PR covering all cortex M use cases.
Also an archi rework should be considered to properly cover suspend to ram scenario.
For instance we should just re-init (possibly breaking application changes) or save/restore (respecting the run-time modifications) ?

[msmttchr]

I think this problem has been addressed in https://github.com/zephyrproject-rtos/zephyr/blob/34e47f4040c99d52fe0e5d5eb64b2904e14f8981/soc/nordic/nrf54h/pm_s2ram.c
In particular, I see saving and restore of the following ARM functions:

• NVIC
• SCB
• MPU

I believe that most code in this part can be moved to arch/arm, but I am not sure about this.
On the other hand, I see nothing related to FPU.