[PATCH net-next v3 0/3] net: wwan: support DTR/RTS on AT ports via MHI IP_CTRL

[Peter Hunt]

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
exposed AT ports but never signalled DTR, so URCs never reached userspace.

Patch 1 extends the wwan core with an optional ->dtr_rts(port, on) port
op, mirroring tty_port_operations.dtr_rts.  The TIOCM bitmask state is
tracked entirely in the wwan core; drivers receive only a simple boolean
assert/de-assert signal.  The core also raises DTR/RTS on first open of
any AT port whose driver implements ->dtr_rts, and drops them on last
close, mirroring TTY semantics without requiring each driver to duplicate
that logic.

Patch 2 enables the IP_CTRL MHI channel in the Sierra PCI table so that
the IP_CTRL driver (patch 3) is actually bound on those controllers.

Patch 3 adds a second mhi_driver that binds the IP_CTRL channel and
registers a ->dtr_rts op so that the wwan core's open/close DTR raise/drop
and userspace TIOCMSET calls both reach the modem.  The existing AT/QMI/MBIM
data path is untouched.

v2: https://lore.kernel.org/netdev/20260806155253.3378294-1-peter.hunt@xxxxxxxxxxxx/

v3:
- Replace ->tiocmget/->tiocmset port ops with a single ->dtr_rts(port, on)
  callback modelled on tty_port_operations.dtr_rts; TIOCM bitmask state
  stays in the wwan core (Loic Poulain)
- Move DTR/RTS raise on AT port open and drop on last close into
  wwan_port_op_start/wwan_port_op_stop in the wwan core (Loic Poulain)
- Remove is_at_port from struct mhi_wwan_dev; rely on wwan core instead
  (Loic Poulain)

Peter Hunt (3):
  net: wwan: core: propagate modem control signals to port drivers
  bus: mhi: host: pci_generic: enumerate IP_CTRL channel for Sierra
    EM919x/EM929x
  net: wwan: mhi_wwan_ctrl: drive DTR/RTS via the IP_CTRL channel

 drivers/bus/mhi/host/pci_generic.c |   2 +
 drivers/net/wwan/mhi_wwan_ctrl.c   | 172 ++++++++++++++++++++++++++++-
 drivers/net/wwan/wwan_core.c       |  18 ++-
 include/linux/wwan.h               |   3 +
 4 files changed, 193 insertions(+), 2 deletions(-)

-- 
2.43.0