[PATCH v4 05/13] USB: ch341: reinitialize chip on reconfiguration

[Grigori Goronzy <greg@chown.ath.cx>]

Changing the LCR register after initialization does not seem to be
reliable on all chips (particularly not on CH341A).  Restructure
initialization and configuration to always reinit the chip on
configuration changes instead and pass the LCR register value directly
to the initialization command.

v2: get rid of unused variable, improve error handling.

Tested-by: Ryan Barber <rfb@skyscraper.nu>
Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
---
 drivers/usb/serial/ch341.c | 47 ++++++++++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 22 deletions(-)

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 95c8a40..6181616 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -61,6 +61,8 @@
  * the Net/FreeBSD uchcom.c driver by Takanori Watanabe.  Domo arigato.
  */
 
+#define CH341_SERIAL_INIT      0xA1
+#define CH341_VERSION          0x5F
 #define CH341_MODEM_CTRL       0xA4
 #define CH341_REQ_WRITE_REG    0x9A
 #define CH341_REQ_READ_REG     0x95
@@ -129,10 +131,10 @@ static int ch341_control_in(struct usb_device *dev,
 	return r;
 }
 
-static int ch341_set_baudrate(struct usb_device *dev,
-			      struct ch341_private *priv)
+static int ch341_init_set_baudrate(struct usb_device *dev,
+			      struct ch341_private *priv, unsigned ctrl)
 {
-	short a, b;
+	short a;
 	int r;
 	unsigned long factor;
 	short divisor;
@@ -152,11 +154,8 @@ static int ch341_set_baudrate(struct usb_device *dev,
 
 	factor = 0x10000 - factor;
 	a = (factor & 0xff00) | divisor;
-	b = factor & 0xff;
 
-	r = ch341_control_out(dev, 0x9a, 0x1312, a);
-	if (!r)
-		r = ch341_control_out(dev, 0x9a, 0x0f2c, b);
+	r = ch341_control_out(dev, CH341_SERIAL_INIT, 0x9c | (ctrl << 8), a | 0x80);
 
 	return r;
 }
@@ -177,7 +176,7 @@ static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
 	if (!buffer)
 		return -ENOMEM;
 
-	r = ch341_control_in(dev, 0x95, 0x0706, 0, buffer, size);
+	r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x0706, 0, buffer, size);
 	if (r < 0)
 		goto out;
 
@@ -207,24 +206,20 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
 		return -ENOMEM;
 
 	/* expect two bytes 0x27 0x00 */
-	r = ch341_control_in(dev, 0x5f, 0, 0, buffer, size);
+	r = ch341_control_in(dev, CH341_VERSION, 0, 0, buffer, size);
 	if (r < 0)
 		goto out;
 
-	r = ch341_control_out(dev, 0xa1, 0, 0);
-	if (r < 0)
-		goto out;
-
-	r = ch341_set_baudrate(dev, priv);
+	r = ch341_control_out(dev, CH341_SERIAL_INIT, 0, 0);
 	if (r < 0)
 		goto out;
 
 	/* expect two bytes 0x56 0x00 */
-	r = ch341_control_in(dev, 0x95, 0x2518, 0, buffer, size);
+	r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x2518, 0, buffer, size);
 	if (r < 0)
 		goto out;
 
-	r = ch341_control_out(dev, 0x9a, 0x2518, 0x0050);
+	r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x2518, 0x00c3);
 	if (r < 0)
 		goto out;
 
@@ -233,11 +228,7 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
 	if (r < 0)
 		goto out;
 
-	r = ch341_control_out(dev, 0xa1, 0x501f, 0xd90a);
-	if (r < 0)
-		goto out;
-
-	r = ch341_set_baudrate(dev, priv);
+	r = ch341_init_set_baudrate(dev, priv, 0);
 	if (r < 0)
 		goto out;
 
@@ -352,16 +343,28 @@ static void ch341_set_termios(struct tty_struct *tty,
 	struct ch341_private *priv = usb_get_serial_port_data(port);
 	unsigned baud_rate;
 	unsigned long flags;
+	unsigned char ctrl;
+	int r;
+
+	/* redundant changes may cause the chip to lose bytes */
+	if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
+		return;
 
 	baud_rate = tty_get_baud_rate(tty);
 
 	priv->baud_rate = baud_rate;
 
+	ctrl = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8;
+
 	if (baud_rate) {
 		spin_lock_irqsave(&priv->lock, flags);
 		priv->line_control |= (CH341_BIT_DTR | CH341_BIT_RTS);
 		spin_unlock_irqrestore(&priv->lock, flags);
-		ch341_set_baudrate(port->serial->dev, priv);
+		r = ch341_init_set_baudrate(port->serial->dev, priv, ctrl);
+		if (r < 0 && old_termios) {
+			priv->baud_rate = tty_termios_baud_rate(old_termios);
+			tty_termios_copy_hw(&tty->termios, old_termios);
+		}
 	} else {
 		spin_lock_irqsave(&priv->lock, flags);
 		priv->line_control &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
-- 
1.9.1