From 10f51f4fb99de99c64b9d35707f05fa0308f25ff Mon Sep 17 00:00:00 2001 From: Peter Hunt Date: Tue, 27 Oct 2026 11:10:55 -0600 Subject: [PATCH] net: wwan: mhi_wwan_ctrl: send a DTR drop before it can be coalesced 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: d509edf90bc6 ("net: wwan: mhi_wwan_ctrl: drive DTR/RTS via the IP_CTRL channel") Suggested-by: Loic Poulain Signed-off-by: Peter Hunt Reviewed-by: Loic Poulain Signed-off-by: Dave Miller --- drivers/net/wwan/mhi_wwan_ctrl.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/net/wwan/mhi_wwan_ctrl.c b/drivers/net/wwan/mhi_wwan_ctrl.c index e3c207588956..772319927867 100644 --- a/drivers/net/wwan/mhi_wwan_ctrl.c +++ b/drivers/net/wwan/mhi_wwan_ctrl.c @@ -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); }