netdev - MHI DTR client implementation

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Date:   Tue, 20 Sep 2022 16:23:25 +0200
From:   Daniele Palmas <dnlplm@...il.com>
To:     mhi@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>
Subject: MHI DTR client implementation

Hello all,

I'm looking for some guidance related to  a possible MHI client for
serial ports signals management implementation.

Testing the AT channels with Telit modems I noted that unsolicited
indications do not show: the root cause for this is DTR not set for
those ports through MHI channels 18/19, something that with current
upstream code can't be done due to the missing DTR client driver.

I currently have an hack, based on the very first mhi stack submission
(see https://lore.kernel.org/lkml/1524795811-21399-2-git-send-email-sdias@codeaurora.org/#Z31drivers:bus:mhi:core:mhi_dtr.c),
solving my issue, but I would like to understand which would be the
correct way, so maybe I can contribute some code.

Should the MHI DTR client be part of the WWAN subsystem? If yes, does
it make sense to have an associated port exposed as a char device? I
guess the answer is no, since it should be used just by the AT ports
created by mhi_wwan_ctrl, but I'm not sure if that's possible.

Or should the DTR management be somehow part of the MHI stack and
mhi_wwan_ctrl interacts with that through exported functions?

Thanks a lot in advance,
Daniele