mcuboot with enabled serial recovery does not compile

[de-nordic]

Describe the bug
The mcuboot, selected by west, does not compile since b852501 commit to Zephyr.

To Reproduce
0. Download overlay file and replace with the download dir

1. Go to zephyr root
2. west build -b nrf52840dk_nrf52840 --build-dir voot bootloader/mcuboot/boot/zephyr/ -t menuconfig -- -DOVERLAY_CONFIG=<dir_to>/serial-recovery.overlay.txt
3. See linker error

Expected behavior
A clear and concise description of what you expected to happen.

Impact
Not able to compile mcuboot for serial recovery.

Environment (please complete the following information):

• OS: Ubuntu 20
• Toolchain zephyr sdk 0.12
• Commit 5e9d6d6

serial-recovery.overlay.txt

[nordic-krch]

The issue is MULTITHREADING is off so kernel files for scheduling are not included but there are modules fetched that are using multithreading essentially making it multithreading app.

Is see 2 ways:

• removed CONFIG_MULTITHREADING=n
• fix module to not use multithreading stuff (k_sleep) by replacing it with no-multithreading friendly k_busy_wait.

[de-nordic]

Is see 2 ways:

* removed `CONFIG_MULTITHREADING=n`

* fix module to not use multithreading stuff (`k_sleep`) by replacing it with no-multithreading friendly `k_busy_wait`.

The removal significantly increase the binary size (4k)

The problem is with z_impl_k_sleep and z_pm_save_idle_exit and and one seems to be reported from zephyr/drivers/serial/libdrivers__serial.a(uart_nrfx_uarte.c.obj) and the other from zephyr/arch/arch/arm/core/aarch32/libarch__arm__core__aarch32.a(isr_wrapper.S.obj)

[nordic-krch]

I will make PR to fix it in uarte driver. As for z_pm_save_idle_exit can you check if CONFIG_PM=n helps? Power management is not supported when multithreading is off.

[nordic-krch]

Actually, there is already a fix in uarte:

zephyr/drivers/serial/uart_nrfx_uarte.c

Line 494 in 977aba6

k_msleep(1);

can you check if that is not working in this case?

[nvlsianpu]

@nordic-krch

Actually, there is already a fix in uarte:
...

Yes, but it is compiled-out using complier, and now need to use preprocessor instead.
Easy to fix then :D

[nvlsianpu]

MCUboot upstream fix: mcu-tools/mcuboot#1009