Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Sheng Long Wang <china_shenglong@163.com>
To:     johan@kernel.org, gregkh@linuxfoundation.org
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        jan.kiszka@siemens.com,
        Wang Sheng Long <shenglong.wang.ext@siemens.com>
Subject: [PATCH] usb-serial:cp210x: add support to software flow control
Date:   Thu, 30 Jul 2020 15:59:22 +0800
Message-Id: <20200730075922.28041-1-china_shenglong@163.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Wang Sheng Long <shenglong.wang.ext@siemens.com>

When data is transmitted between two serial ports,
the phenomenon of data loss often occurs. The two kinds
of flow control commonly used in serial communication
are hardware flow control and software flow control.

In serial communication, If you only use RX/TX/GND Pins, you
can't do hardware flow. So we often used software flow control
and prevent data loss. The user sets the software flow control
through the application program, and the application program
sets the software flow control mode for the serial port
chip through the driver.

For the cp210 serial port chip, its driver lacks the
software flow control setting code, so the user cannot set
the software flow control function through the application
program. This adds the missing software flow control.

Signed-off-by: Wang Sheng Long <shenglong.wang.ext@siemens.com>
---
 drivers/usb/serial/cp210x.c | 118 ++++++++++++++++++++++++++++++++++--
 1 file changed, 113 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index e732949f65..c66a0e0fb9 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -380,6 +380,9 @@ static struct usb_serial_driver * const serial_drivers[] = {
 #define CP210X_PARTNUM_CP2102N_QFN20	0x22
 #define CP210X_PARTNUM_UNKNOWN	0xFF
 
+#define CP210X_VSTART	0x11
+#define CP210X_VSTOP	0x13
+
 /* CP210X_GET_COMM_STATUS returns these 0x13 bytes */
 struct cp210x_comm_status {
 	__le32   ulErrors;
@@ -391,6 +394,15 @@ struct cp210x_comm_status {
 	u8       bReserved;
 } __packed;
 
+struct cp210x_chars_response {
+	u8	eofchar;
+	u8	errochar;
+	u8	breakchar;
+	u8	eventchar;
+	u8	xonchar;
+	u8	xoffchar;
+} __packed;
+
 /*
  * CP210X_PURGE - 16 bits passed in wValue of USB request.
  * SiLabs app note AN571 gives a strange description of the 4 bits:
@@ -624,6 +636,45 @@ static int cp210x_read_vendor_block(struct usb_serial *serial, u8 type, u16 val,
 	return result;
 }
 
+/*
+ * Read and Write Character Responses operate
+ * Register SET_CHARS/GET_CHATS
+ */
+static int cp210x_operate_chars_block(struct usb_serial_port *port,
+				u8 req, u8 type, void *buf, int bufsize)
+{
+	struct usb_serial *serial = port->serial;
+	struct cp210x_port_private *port_priv = usb_get_serial_port_data(port);
+	void *dmabuf;
+	int result;
+
+	dmabuf = kmemdup(buf, bufsize, GFP_KERNEL);
+	if (!dmabuf)
+		return -ENOMEM;
+
+	result = usb_control_msg(serial->dev,
+				usb_rcvctrlpipe(serial->dev, 0),
+				req, type, 0, port_priv->bInterfaceNumber,
+				dmabuf, bufsize, USB_CTRL_SET_TIMEOUT);
+
+	if (result == bufsize) {
+		if (type == REQTYPE_DEVICE_TO_HOST)
+			memcpy(buf, dmabuf, bufsize);
+
+		result = 0;
+	} else {
+		dev_err(&port->dev, "failed get req 0x%x size %d status: %d\n",
+			req, bufsize, result);
+		if (result >= 0)
+			result = -EIO;
+
+	}
+
+	kfree(dmabuf);
+
+	return result;
+}
+
 /*
  * Writes any 16-bit CP210X_ register (req) whose value is passed
  * entirely in the wValue field of the USB request.
@@ -1134,11 +1185,17 @@ static void cp210x_set_termios(struct tty_struct *tty,
 		struct usb_serial_port *port, struct ktermios *old_termios)
 {
 	struct device *dev = &port->dev;
-	unsigned int cflag, old_cflag;
+	struct cp210x_chars_response charsres;
+	struct cp210x_flow_ctl flow_ctl;
+	unsigned int cflag, old_cflag, iflag;
 	u16 bits;
+	int result;
+	u32 ctl_hs;
+	u32 flow_repl;
 
 	cflag = tty->termios.c_cflag;
 	old_cflag = old_termios->c_cflag;
+	iflag = tty->termios.c_iflag;
 
 	if (tty->termios.c_ospeed != old_termios->c_ospeed)
 		cp210x_change_speed(tty, port, old_termios);
@@ -1212,10 +1269,6 @@ static void cp210x_set_termios(struct tty_struct *tty,
 	}
 
 	if ((cflag & CRTSCTS) != (old_cflag & CRTSCTS)) {
-		struct cp210x_flow_ctl flow_ctl;
-		u32 ctl_hs;
-		u32 flow_repl;
-
 		cp210x_read_reg_block(port, CP210X_GET_FLOW, &flow_ctl,
 				sizeof(flow_ctl));
 		ctl_hs = le32_to_cpu(flow_ctl.ulControlHandshake);
@@ -1252,6 +1305,61 @@ static void cp210x_set_termios(struct tty_struct *tty,
 				sizeof(flow_ctl));
 	}
 
+	/*
+	 * Set Software  Flow  Control
+	 * Check the IXOFF/IXON status in the iflag component of the
+	 * termios structure.
+	 *
+	 */
+	if ((iflag & IXOFF) || (iflag & IXON)) {
+
+		result = cp210x_operate_chars_block(port,
+						CP210X_GET_CHARS,
+						REQTYPE_DEVICE_TO_HOST,
+						&charsres,
+						sizeof(charsres));
+
+		if (result < 0) {
+			dev_err(dev, "Read Characrter Responses failed\n");
+			return;
+		}
+		charsres.xonchar  = CP210X_VSTART;
+		charsres.xoffchar = CP210X_VSTOP;
+		result = cp210x_operate_chars_block(port,
+						CP210X_SET_CHARS,
+						REQTYPE_HOST_TO_INTERFACE,
+						&charsres,
+						sizeof(charsres));
+		if (result < 0) {
+			memset(&charsres, 0, sizeof(charsres));
+			dev_err(dev, "Write Characrter Responses failed\n");
+			return;
+		}
+
+		/* Set  Rx/Tx Flow Control Flag in ulFlowReplace */
+		cp210x_read_reg_block(port,
+					CP210X_GET_FLOW,
+					&flow_ctl,
+					sizeof(flow_ctl));
+
+		flow_repl = le32_to_cpu(flow_ctl.ulFlowReplace);
+
+		if (iflag & IXOFF)
+			flow_repl |= CP210X_SERIAL_AUTO_RECEIVE;
+		else
+			flow_repl &= ~CP210X_SERIAL_AUTO_RECEIVE;
+
+		if (iflag & IXON)
+			flow_repl |= CP210X_SERIAL_AUTO_TRANSMIT;
+		else
+			flow_repl &= ~CP210X_SERIAL_AUTO_TRANSMIT;
+
+		flow_ctl.ulFlowReplace = cpu_to_le32(flow_repl);
+		cp210x_write_reg_block(port,
+					CP210X_SET_FLOW,
+					&flow_ctl,
+					sizeof(flow_ctl));
+	}
 }
 
 static int cp210x_tiocmset(struct tty_struct *tty,
-- 
2.17.1