Serial DFU and Shell on same UART interface

[MortenK]

Using nRF9160. Using NCS 2.6.0. Building for the nRF9160DK with nRF9160.

We were wondering if there's a way to enable both the shell and serial bootloader on the same interface.

So far we have:

• Created a simple blinky DFU application based on (Add DFU support to your application) and can see the bootloader works as expected.
• Based on the guide, there's an option to share the UART console with the MCUMGR transport, which we have enabled and appears to work.
  """Another option is to use the configs from smp_svr/overlay-serial-console.config to enable the UART console with mcumgr pass through. """

We'd like to push this further to enable the shell on this UART console.

However, simply enabling the shell via CONFIG_SHELL=y appears to hang the device pretty soon after boot. (The debugger seems to indicate the program hangs in shell_init() waiting for pending UART Tx to complete.)
Pushing the shell elsewhere (e.g. RTT) builds and runs successfully, but we would ideally share the shell interface with the MCUMGR transport.

Is there any way to do this via existing kconfig options / SDK patches?

[MortenK]

We were going about it slightly wrong. Instead of enabling UART passthrough, this can be achieved by activating the shell and simply using shell as the transport layer with

CONFIG_MCUMGR_TRANSPORT_SHELL=y