shell: uart: Allow a change in the shell initalisation to let routing it through USB UART

[KubaFYI]

Is your enhancement proposal related to a problem? Please describe.
When wanting to route the shell through USB CDC ACM there is a problem with the shell getting possibly initialised before the CDC ACM driver.

Describe the solution you'd like
I managed to successfully accomplish what I need by adding a call to usb_enable() in the enable_shell_uart() function and changing the literal 0 shell initialisation priority to CONFIG_APPLICATION_INIT_PRIORITY (so that it happens after the USB device's CONFIG_KERNEL_INIT_PRIORITY_DEVICE.

However, I'm not sure if this is the correct way to do it with me being possibly unaware of the reason why shell's initialisation needs to be 0, an the best place to usb_enable().

[KubaFYI]

I've done the work on my fork at https://github.com/KubaFYI/zephyr/tree/feat_usb_acm_shell.

[carlescufi]

I've done the work on my fork at https://github.com/KubaFYI/zephyr/tree/feat_usb_acm_shell.

Why don't you send an RFC PR with the code you have and we then discuss it there?

[KubaFYI]

@carlescufi Oh ok. I always kinda assumed it's annoying to bother everyone with PRs which have not been discussed to be the right way forward, but if that's the preferred workflow I'll go for it!

[carlescufi]

@carlescufi Oh ok. I always kinda assumed it's annoying to bother everyone with PRs which have not been discussed to be the right way forward, but if that's the preferred workflow I'll go for it!

No actually, many discussions can take place directly in the PR. Thanks for your contribution!

[jfischer-no]

The solution in current Zephyr tree is to configure the shell (CONFIG_UART_SHELL_ON_DEV_NAME="CDC_ACM_0") and enable USB device support in user application.
See also #26122 (comment)