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net: wwan: mhi_wwan_ctrl: send a DTR drop before it can be coalesced

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DTR/RTS changes are sent from a work item that only sends the latest
state, so a drop followed quickly by a raise, for example TIOCMBIC then
TIOCMBIS or a quick close and reopen, can reach the modem as just the
raise. A drop matters on its own, a modem set to AT&D2 hangs up on it.

Flush the work when DTR goes low so the drop is sent before ->dtr_rts()
returns, and flush it in stop() so any pending state is sent before the
channel is stopped. A drop that hits a full UL ring is still retried
with whatever state is latest by then.

Fixes: d509edf90b ("net: wwan: mhi_wwan_ctrl: drive DTR/RTS via the IP_CTRL channel")
Suggested-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Signed-off-by: Peter Hunt <peter.hunt@opengear.com>
Reviewed-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Signed-off-by: Dave Miller <davem@davem-thinkpadp1gen8.ibmlond.csb>
This commit is contained in:
Peter Hunt 2026-10-27 11:10:55 -06:00 committed by Dave Miller
parent c4ba171685
commit 10f51f4fb9
1 changed files with 11 additions and 0 deletions
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11
drivers/net/wwan/mhi_wwan_ctrl.c
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@ -209,9 +209,17 @@ static void mhi_wwan_ctrl_dtr_work(struct work_struct *work)
static void mhi_wwan_ctrl_dtr_rts(struct wwan_port *port, unsigned int mdmbits)
{
struct mhi_wwan_dev *mhiwwan = wwan_port_get_drvdata(port);
bool drop = (READ_ONCE(mhiwwan->dtr_mdmbits) & TIOCM_DTR) &&
!(mdmbits & TIOCM_DTR);
WRITE_ONCE(mhiwwan->dtr_mdmbits, mdmbits);
schedule_delayed_work(&mhiwwan->dtr_work, 0);
/* A DTR drop matters on its own, e.g. to hang up a modem set to AT&D2,
* so send it now rather than let a following raise coalesce it away
*/
if (drop)
flush_delayed_work(&mhiwwan->dtr_work);
}
static int mhi_wwan_ctrl_start(struct wwan_port *port)
@ -246,6 +254,9 @@ static void mhi_wwan_ctrl_stop(struct wwan_port *port)
cancel_work_sync(&mhiwwan->rx_refill);
/* Send any pending DTR/RTS state before the channel stops */
flush_delayed_work(&mhiwwan->dtr_work);
mhi_unprepare_from_transfer(mhiwwan->mhi_dev);
}