osmo-bts-trx channel activation

Hi.

This has been asked last year but to no avail, let's try again.

How logical channels are (de)activated in osmo-bts-trx? For example in all the other models there's sapi_deactivate_cb() callback but osmo-bts-trx doesn't seem to be using sapi_cmd at all.

To put this into perspective - while working on https://projects.osmocom.org/issues/1575 I got to activate/deactivate lchans when SI3 is received. This already works for sysmobts but I'd like to do the same for osmo-bts-trx as well.

Is there any documentation somewhere describing how it works there? Or maybe someone more familiar with the code could help to shed the light on it?