[PATCH] usb-serial:cp210x: add support to software flow control

[PATCH] usb-serial:cp210x: add support to software flow control

[Sheng Long Wang]

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

Re: [PATCH] usb-serial:cp210x: add support to software flow control

[Greg KH]

On Thu, Jul 30, 2020 at 03:59:22PM +0800, Sheng Long Wang wrote:
> 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(-)

What changed from the previous version of this patch?  That should be
described below the --- line and this is a v2, right?

thanks,

greg k-h

Re: Re: [PATCH] usb-serial:cp210x: add support to software flow control

[Greg KH]

On Thu, Jul 30, 2020 at 04:32:37PM +0800, china_shenglong wrote:
> Hi, Greg
> 
> 
> Yeah, It mainly adjusts the code style according to the kernel specification,
> and then modifies it according to your previous review comments.

Always include that below the --- line, and version your patches so we
have a chance to know what is going on.

please fix up and resend.

thanks,

greg k-h-

Re: [PATCH] usb-serial:cp210x: add support to software flow control

[Jan Kiszka]

On 30.07.20 10:32, china_shenglong wrote:
> Hi, Greg
> 
> Yeah, It mainly adjusts the code style according to the kernel
> specification,
> and then modifies it according to your previous review comments.
> 
> Thanks,
> 
> BR/ Wang ShengLong
> 
> 
> At 2020-07-30 16:06:39, "Greg KH" <gregkh@linuxfoundation.org> wrote:
>>On Thu, Jul 30, 2020 at 03:59:22PM +0800, Sheng Long Wang wrote:
>>> 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(-)
>>
>>What changed from the previous version of this patch?  That should be
>>described below the --- line and this is a v2, right?
>>
>>thanks,
>>
>>greg k-h

This no longer applies. Shenglong, could you send a rebased version as v3?
Please also include a changelog after the "---" separator this time.

Thanks,
Jan

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