How to disable STM32MP1 cortex M4 core

[PGE]

We are using a STM32MP157 chip on a custom low-power design and don't need the Cortex M4 core. We would like to disable it properly to reduce power consumption and also remove dedicated support in linux kernel.

Is there any recommended way to do this ? Is disabling clock enough ?

Thanks in advance for your help

[PatrickF · Accepted solution]

Hi,

You usually have nothing to do.

Cortex-M4 is disabled by default (i.e. MCU is in HOLD_BOOT, i.e. Cortex-M4 core clocks are stopped), unless it is specifically started (see https://wiki.st.com/stm32mpu/wiki/How_to_start_the_coprocessor_from_the_bootloader)

Similar root clock gating is available for peripherals , i.e. if no related peripherals are assign to m4 in the device tree, their clock sources are not started by Linux. (See https://wiki.st.com/stm32mpu/wiki/How_to_assign_an_internal_peripheral_to_a_runtime_context)

Note that many peripherals, which could be assigned to Linux runtime context, reside on 'MCU side', so when Linux is running and those peripherals are active, the related buses could be active too.

There is no power switch able to remove the static leakage for the unused portion of the device (including Cortex-M4, memories, peripherals).

Regards,

Patrick

[PGE]

Ok so I believe it's disabled already.

Then do you confirm I can also remove all rproc related things in the device tree files ?

Thank you

Patrick

[PatrickF]

no need to remove (there could be side effects), just ensure nodes are:

status = "disabled";

But CubeMX should generate it for you.

Regards,

[PGE]

ok thanks

[PatrickF]

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