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[Medium] a DTR/RTS request made while IP_CTRL is not bound is lost: agreed. It needs IP_CTRL to bind after the AT port has been opened. On the EM919x/EM929x, IP_CTRL (channels 18/19) is probed before DUN (32/33), so outside async probing this only happens after a sysfs unbind/rebind of mhi_wwan_dtr or a failed IP_CTRL probe. The fix is for mhi_wwan_dtr_probe() to resend the current state of the AT ports on its controller. [Low] coalescing can swallow a DTR drop on a quick close and reopen: agreed, a drop matters on its own for a modem set to AT&D2. The fix is to never coalesce away a pending drop, and send it before the latest state. Both are corner cases outside normal operation, which I've tested on an EM9291, including bursts of 10,000 DTR changes ending in either state. I'd propose to address them in a small follow-up patch on top of this series, but I'm happy to fold them into a v11 instead if the maintainers prefer.