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Fri, 26 Jun 2020 04:24:20 +0000 From: Phu Luu To: "johan@kernel.org" , "gregkh@linuxfoundation.org" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: Brant Merryman , Richard Hendricks , =?windows-1258?Q?Ph=FA_L=FDu_An?= , "hungnd3@fsoft.com.vn" Subject: [PATCH v3 2/2] USB: serial: cp210x: Proper RTS control when buffers fill Thread-Topic: [PATCH v3 2/2] USB: serial: cp210x: Proper RTS control when buffers fill Thread-Index: AQHWS3Gpakt8lWkQAEeJtxJ+vFX8Lg== Date: Fri, 26 Jun 2020 04:24:20 +0000 Message-ID: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: kernel.org; dkim=none (message not signed) header.d=none;kernel.org; dmarc=none action=none header.from=silabs.com; x-originating-ip: [59.153.237.173] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 03ca8aa3-63a4-4581-b8ae-08d81988cbfe x-ms-traffictypediagnostic: DM6PR11MB3290: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:1186; 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charset="windows-1258" Content-ID: <248726EE79415944BD0B7ED5144C1F9D@namprd11.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: silabs.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DM6PR11MB2857.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 03ca8aa3-63a4-4581-b8ae-08d81988cbfe X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Jun 2020 04:24:20.0800 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 54dbd822-5231-4b20-944d-6f4abcd541fb X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: RH4hRQQY0HYfB446Y6b00+vyyiGkMuXnzFD9vyPkF+tfRJMNp9gFi+4SbpLZzcxlpJzYJIIW1r+A75ZLelo0Dg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR11MB3290 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Brant Merryman CP210x hardware disables auto-RTS but leaves auto-CTS when in hardware flow control mode and UART on cp210x hardware is disabled. This allows data to flow out, but new data will not come into the port. When re-opening the port, if auto-CTS is enabled on the cp210x, then auto-RTS must be re-enabled in the driver. Signed-off-by: Phu Luu Signed-off-by: Brant Merryman --- 06/09/2020: Patch v3 2/2 Modified based on feedback from Johan Hovold 12/18/2019: Patch v2 Broken into two patches and modified based on feedback= from Johan Hovold 12/09/2019: Initial submission of patch "Proper RTS control when buffers fi= ll" drivers/usb/serial/cp210x.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c index bcceb4ad8be0..091441b1c5b9 100644 --- a/drivers/usb/serial/cp210x.c +++ b/drivers/usb/serial/cp210x.c @@ -917,6 +917,7 @@ static void cp210x_get_termios_port(struct usb_serial_p= ort *port, u32 baud; u16 bits; u32 ctl_hs; + u32 flow_repl; =20 cp210x_read_u32_reg(port, CP210X_GET_BAUDRATE, &baud); =20 @@ -1017,6 +1018,23 @@ static void cp210x_get_termios_port(struct usb_seria= l_port *port, ctl_hs =3D le32_to_cpu(flow_ctl.ulControlHandshake); if (ctl_hs & CP210X_SERIAL_CTS_HANDSHAKE) { dev_dbg(dev, "%s - flow control =3D CRTSCTS\n", __func__); + /* + * When the port is closed, the CP210x hardware disables + * auto-RTS and RTS is deasserted but it leaves auto-CTS when + * in hardware flow control mode. This prevents new data from + * being received by the port. When re-opening the port, if + * auto-CTS is enabled on the cp210x, then auto-RTS must be + * re-enabled in the driver. + */ + flow_repl =3D le32_to_cpu(flow_ctl.ulFlowReplace); + flow_repl &=3D ~CP210X_SERIAL_RTS_MASK; + flow_repl |=3D CP210X_SERIAL_RTS_SHIFT(CP210X_SERIAL_RTS_FLOW_CTL); + flow_ctl.ulFlowReplace =3D cpu_to_le32(flow_repl); + cp210x_write_reg_block(port, + CP210X_SET_FLOW, + &flow_ctl, + sizeof(flow_ctl)); + cflag |=3D CRTSCTS; } else { dev_dbg(dev, "%s - flow control =3D NONE\n", __func__); --=20 2.17.0