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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Daniele Palmas , linux-kernel@vger.kernel.org, Peter Hunt Subject: [PATCH net v2] net: wwan: mhi_wwan_ctrl: send a DTR drop before it can be coalesced Date: Tue, 27 Oct 2026 11:10:55 -0600 Message-ID: <20261027171055.1796482-1-peter.hunt@opengear.com> X-Mailer: git-send-email 2.43.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: SJ0PR03CA0171.namprd03.prod.outlook.com (2603:10b6:a03:338::26) To MWHPR1001MB2095.namprd10.prod.outlook.com (2603:10b6:301:32::34) X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MWHPR1001MB2095:EE_|BLAPR10MB5057:EE_ X-MS-Office365-Filtering-Correlation-Id: 917434d6-92ca-4558-e5ee-08df344d4535 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|23010399003|1800799024|366016|261026121527099003|18002099003|11063799006|261021121427099003|56012099006|10067099003|261021123027099003|261009223027099003|261022075727099003|261022105027099003|261026140227099003; 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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 --- v2: Only handle the DTR drop, by flushing the work when DTR goes low, and flush it in stop() as well (Loic Poulain). Drop the port list and resend on a late IP_CTRL bind, which is only reachable by unbinding and rebinding mhi_wwan_dtr through sysfs. v1: https://lore.kernel.org/all/20261023174113.2388353-1-peter.hunt@opengear.com/ Tested on a Sierra EM9291 (CM8100): back-to-back DTR drop+raise and close+reopen now always send the drop, bursts of 10,000 DTR changes, HUPCL, teardown and lock stress tests. 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); } -- 2.43.0