Mcumgr not working with `CONFIG_MCUMGR_TRANSPORT_SHELL`+`CONFIG_SHELL_BACKEND_SERIAL_API_POLLING`

[JaagupAverin]

Describe the bug

Issue:

Was trying to test mcumgr/SMP with native_sim but the SMP commands would get regular shell responses in form of AAsIAAABAAAABqBzEw==: command not found
However it appears this issue applies to CONFIG_SHELL_BACKEND_SERIAL_API_POLLING=y in general, which is the default for native_sim.

Some investigation:

• CONFIG_MCUMGR_TRANSPORT_SHELL only hooks into the interrupt/async shell backend. In zephyr/subsys/shell/backends/shell_uart.c:70-132.
• The polling backend (zephyr/subsys/shell/backends/shell_uart.c:263-309) never calls smp_shell_rx_bytes(). When the build ends up with CONFIG_SHELL_BACKEND_SERIAL_API_POLLING=y (the default for native_sim), every SMP byte is treated as ordinary shell input.
• Kconfig doesn’t express this incompatibility, so you can enable CONFIG_MCUMGR_TRANSPORT_SHELL together with the polling backend and get a silently non-working configuration.

Fix:

CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_SHELL_BACKEND_SERIAL_INTERRUPT_DRIVEN=y
CONFIG_SHELL_BACKEND_SERIAL_API_INTERRUPT_DRIVEN=y

Desired outcome:

At least a Kconfig conflict.

Regression

• This is a regression.

Steps to reproduce

No response

Relevant log output

Impact

Annoyance – Minor irritation; no significant impact on usability or functionality.

Environment

No response

Additional Context

No response

[nordicjm]

Not a MCUmgr problem, reassigning to shell