Commit 55fa15b5 authored by Johan Hovold's avatar Johan Hovold
Browse files

USB: serial: ch341: fix baud rate and line-control handling 



Revert to using direct register writes to set the divisor and
line-control registers.

A recent change switched to using the init vendor command to update
these registers, something which also enabled support for CH341A
devices. It turns out that simply setting bit 7 in the divisor register
is sufficient to support CH341A and specifically prevent data from being
buffered until a full endpoint-size packet (32 bytes) has been received.

Using the init command also had the side-effect of temporarily
deasserting the DTR/RTS signals on every termios change (including
initialisation on open) something which for example could cause problems
in setups where DTR is used to trigger a reset.

Fixes: 4e46c410 ("USB: serial: ch341: reinitialize chip on
reconfiguration")
Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
parent 3cca8624

drivers/usb/serial/ch341.c

+17 −7
Original line number Diff line number Diff line
@@ -133,8 +133,8 @@ static int ch341_control_in(struct usb_device *dev, 
	return r;

}



static int ch341_init_set_baudrate(struct usb_device *dev,

				   struct ch341_private *priv, unsigned ctrl)

static int ch341_set_baudrate_lcr(struct usb_device *dev,

				  struct ch341_private *priv, u8 lcr)

{

	short a;

	int r;
@@ -157,9 +157,19 @@ static int ch341_init_set_baudrate(struct usb_device *dev, 
	factor = 0x10000 - factor;

	a = (factor & 0xff00) | divisor;



	/* 0x9c is "enable SFR_UART Control register and timer" */

	r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT,

			      0x9c | (ctrl << 8), a | 0x80);

	/*

	 * CH341A buffers data until a full endpoint-size packet (32 bytes)

	 * has been received unless bit 7 is set.

	 */

	a |= BIT(7);



	r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x1312, a);

	if (r)

		return r;



	r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x2518, lcr);

	if (r)

		return r;



	return r;

}
@@ -233,7 +243,7 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv) 
	if (r < 0)

		goto out;



	r = ch341_init_set_baudrate(dev, priv, priv->lcr);

	r = ch341_set_baudrate_lcr(dev, priv, priv->lcr);

	if (r < 0)

		goto out;
@@ -394,7 +404,7 @@ static void ch341_set_termios(struct tty_struct *tty, 
	if (baud_rate) {

		priv->baud_rate = baud_rate;



		r = ch341_init_set_baudrate(port->serial->dev, priv, ctrl);

		r = ch341_set_baudrate_lcr(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);

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