From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=109.224.244.108 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792614395; b=jzlZQYEJOF80vHImduC7raRLP6/LkPBjS2acf0BbZg80vEd2W/i+KEJi4EuSTcQio/KD hp2JfYiw/5JaygcEyXs5kEgFb8pHJZ0lbl5irXoDYWMvMNx8pjqR8A/qeLm2svwwIElZ6 u2xP8BOhHdTYTDMWjBkoxlYmNCmcTgLuiTWAbCSsvN7aJMjOL3T0TXV+DdjoViEz2pWK5 wWyZWXLKq1zTUWFfhqcLHqBxq0Yb7ZePnopwqb28dy02SaI7hd5ganf0BepGzTxhSWeyY d8ul8lCquQuOsUv+IR0tYCRkiB9x010gEWsB2mgKppnOEGob9yWHM/mtAjG8+eAr86Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792614395; h=DMARC-Filter:DKIM-Signature:X-Pm-Submission-Id:From:To:Cc:Subject: Date:Message-ID:X-Mailer:MIME-Version:Content-Transfer-Encoding; bh=E2pTPMKUQJD5SV65KUhENq72igG4uuAAoV5xy1VuYmA=; b=WcV5/CKNxL3279Zw11Ro39+rexqSoS6OjQWqUXQCDZpDDaBSos9YvCmhQT8pBnMTqTxq GH3jRJAgICHoXFzC0MA7DUosdcYxHnFMdrQNPjY7PBoanjWtZkbZgkAUY4aPwTxZMsbT/ EfAyQ9uaZkaSm6Amelne5Bfwp8cSzuoPZrOD38wc3jW7cNNJjqWX02gPWE3HqQLCucsIm 8rqGuOk30eCr5iXvKjRSGXjh2sV+Havg/pizDsKJ80FS0doazPg91qrZJUXHCowR0auSS 6MVaHEFEP+F/NKLk6if5Y1cW3jILDHj0VkxTY01I0pXILvH1VlTL4Rr31bBGaZaV3lA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=michaelmcallister.org; spf=pass smtp.mailfrom=michaelmcallister.org; dkim=pass header.d=michaelmcallister.org header.i=@michaelmcallister.org header.a=rsa-sha256 header.s=protonmail2 header.b=3EIwuN13; arc=none smtp.remote-ip=109.224.244.108 Received: from mail-244108.protonmail.ch (mail-244108.protonmail.ch [109.224.244.108]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B40E0606A324 for ; Wed, 21 Oct 2026 20:26:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org B40E0606A324 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=michaelmcallister.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=michaelmcallister.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=michaelmcallister.org header.i=@michaelmcallister.org header.a=rsa-sha256 header.s=protonmail2 header.b=3EIwuN13 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=michaelmcallister.org; s=protonmail2; t=1792614391; x=1792873591; bh=E2pTPMKUQJD5SV65KUhENq72igG4uuAAoV5xy1VuYmA=; h=From:To:Cc:Subject:Date:Message-ID:From:To:Cc:Date:Subject: Reply-To:Feedback-ID:Message-ID:BIMI-Selector; b=3EIwuN13mRx60PgDwUFijdHtb2b+vrGxOONLJ84KBuHkxbvrlTvXiP/GrDXMHMYnJ iBlDRH9E7UzxG5kukFXg2dbsqfljpjrDzTXoIJTmdY0y1kZxtJ2fmXRotM/Hykr6/7 9WJAG0GJCfIpclPTmVUdBYh21RkzcAr5y/rH8XM7to03gz2MCeMpQ8dmArPyimApNN bEWlTFZcLqtr2P1U0l26pLqi7uLoyzYI0AVsjOmM635YYnsvkHKexAvptEFFaYDxja 85mb76usdedOfCu4p2jr0JkOWLH6tOO62YYgEPktw3Yfg8dnBv7h3IVnyOff08wgSO W1+4MNpWydR/Q== X-Pm-Submission-Id: 4j915f1BsSz2Sccv From: Michael McAllister To: linux-serial@vger.kernel.org Cc: gregkh@linuxfoundation.org, jirislaby@kernel.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] serial: qcom-geni: Set UPSTAT_AUTOCTS for hardware flow control Date: Wed, 21 Oct 2026 21:26:03 +0100 Message-ID: <20261021202603.42888-1-me@michaelmcallister.org> X-Mailer: git-send-email 2.50.1 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit qcom_geni_serial_set_termios() clears UART_CTS_MASK when CRTSCTS is set, enabling hardware CTS flow control. However, it never sets UPSTAT_AUTOCTS, so uart_softcts_mode() also selects software-assisted CTS flow control. If CTS is deasserted when uart_change_line_settings() samples the modem status, serial core sets hw_stopped and stops transmission. The GENI driver does not handle CTS-change interrupts, so asserting CTS again does not clear hw_stopped or restart the transmitter. On a Motorola Moto G10 with WCN3950, this can stall Bluetooth setup in tty_wait_until_sent() while qca_setup() closes the serial port. A captured stall had one byte left in the software transmit queue, hw_stopped set, and CTS asserted, with the UART powered and its interrupt enabled. Set UPSTAT_AUTOCTS under the port lock when CRTSCTS is enabled, and clear it when CRTSCTS is disabled, to match the hardware configuration. Fixes: 8a8a66a1a18a ("tty: serial: qcom_geni_serial: Add support for flow control") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Michael McAllister --- Hardware validation used the same change in the Motorola Moto G10 Linux 7.2.9 port. Before the fix, a Bluetooth power-cycle test captured qca_setup() blocked in tty_wait_until_sent() through serdev_device_close(), with: software TX pending: 1 byte hw_stopped: 1 UART status: 0x1 (UPSTAT_CTS_ENABLE without UPSTAT_AUTOCTS) SE_GENI_IOS: 0x1 (IO2_DATA_IN clear, CTS asserted) UART IRQ disabled: 0 UART IRQ masked: 0 After the fix RTC suspend/resume worked, followed by Bluetooth discovery. Built drivers/tty/serial/qcom_geni_serial.o for arm64 with W=1 and CONFIG_SERIAL_QCOM_GENI_CONSOLE=y against the base below. AI assistance: Codex analyzed the saved UART diagnostics and serial-core source and ran the build and style checks. drivers/tty/serial/qcom_geni_serial.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c index a851b8f0ef..5782b89c84 100644 --- a/drivers/tty/serial/qcom_geni_serial.c +++ b/drivers/tty/serial/qcom_geni_serial.c @@ -1503,6 +1503,7 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport, struct qcom_geni_serial_port *port = to_dev_port(uport); unsigned int baud; unsigned long timeout; + unsigned long flags; u32 bits_per_char; u32 tx_trans_cfg; u32 tx_parity_cfg; @@ -1596,6 +1597,14 @@ static void qcom_geni_serial_set_termios(struct uart_port *uport, writel(bits_per_char, uport->membase + SE_UART_RX_WORD_LEN); writel(stop_bit_len, uport->membase + SE_UART_TX_STOP_BIT_LEN); + /* CTS gates TX in hardware; no CTS interrupt updates hw_stopped. */ + uart_port_lock_irqsave(uport, &flags); + if (termios->c_cflag & CRTSCTS) + uport->status |= UPSTAT_AUTOCTS; + else + uport->status &= ~UPSTAT_AUTOCTS; + uart_port_unlock_irqrestore(uport, flags); + trace_geni_serial_set_termios(uport->dev, baud, bits_per_char, tx_trans_cfg, tx_parity_cfg, rx_trans_cfg, rx_parity_cfg, stop_bit_len); base-commit: a90ee4305c4a5df72c11b31dacfdc76e00fcf78a -- 2.50.1 (Apple Git-155)