Merge branch 'net-wwan-support-dtr-rts-on-at-ports-via-mhi-ip_ctrl'

Peter Hunt says:

====================
net: wwan: support DTR/RTS on AT ports via MHI IP_CTRL

Qualcomm/Sierra SDX55/SDX65 modems (e.g. EM9291) withhold unsolicited AT
result codes until the host asserts DTR. The in-tree mhi_wwan_ctrl driver
exposes AT ports but never signals DTR, so URCs never reach userspace.

Patch 1 extends the wwan core with an optional ->dtr_rts(port, mdmbits)
port op. The TIOCM bitmask state is tracked in the wwan core, which raises
DTR/RTS on first open of an AT port whose driver implements ->dtr_rts,
drops them on last close (if HUPCL is set, which is the default for AT
ports) and on port removal, and passes the resolved bitmask to the
driver on TIOCMSET/TIOCMBIC/TIOCMBIS.

Patch 2 adds a second mhi_driver to mhi_wwan_ctrl that binds the IP_CTRL
channel and implements ->dtr_rts by sending the host serial state to the
modem over that channel. The existing AT/QMI/MBIM data path is untouched.

This is a two-patch series. The pci_generic patch from v5 that
enumerates the IP_CTRL channel for the Sierra EM919x/EM929x has been
applied to mhi-next by Mani as commit 83c29a55b89e ("bus: mhi: host:
pci_generic: Add IP_CTRL channel for Sierra EM919x/EM929x"). There is no
build dependency between the two, without that commit the IP_CTRL driver
simply never binds and ->dtr_rts is a no-op.
====================

Link: https://patch.msgid.link/20261013183500.261229-1-peter.hunt@opengear.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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