This adds support for enabling and disabling RTS/CTS hardware flow control. Tested using a CH340E in combination with a CP2102. Fixes part of the following bug report: Link: https://bugzilla.kernel.org/show_bug.cgi?id=197109 CC: linux-usb@xxxxxxxxxxxxxxx Signed-off-by: Lode Willems <me@xxxxxxxxxxxxxxx> --- drivers/usb/serial/ch341.c | 41 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c index 0870c6533f80..c3b3cae33a41 100644 --- a/drivers/usb/serial/ch341.c +++ b/drivers/usb/serial/ch341.c @@ -63,6 +63,7 @@ #define CH341_REG_DIVISOR 0x13 #define CH341_REG_LCR 0x18 #define CH341_REG_LCR2 0x25 +#define CH341_REG_FLOW_CTL 0x27 #define CH341_NBREAK_BITS 0x01 @@ -77,6 +78,9 @@ #define CH341_LCR_CS6 0x01 #define CH341_LCR_CS5 0x00 +#define CH341_FLOW_CTL_NONE 0x000 +#define CH341_FLOW_CTL_RTSCTS 0x101 + #define CH341_QUIRK_LIMITED_PRESCALER BIT(0) #define CH341_QUIRK_SIMULATE_BREAK BIT(1) @@ -478,6 +482,41 @@ static int ch341_open(struct tty_struct *tty, struct usb_serial_port *port) return r; } +static void ch341_set_flow_control(struct tty_struct *tty, + struct usb_serial_port *port, + const struct ktermios *old_termios) +{ + int r; + + if (old_termios && + C_CRTSCTS(tty) == (old_termios->c_cflag & CRTSCTS)) + return; + + if (C_CRTSCTS(tty)) { + r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG, + CH341_REG_FLOW_CTL | + ((u16)CH341_REG_FLOW_CTL << 8), + CH341_FLOW_CTL_RTSCTS); + if (r < 0) { + dev_err(&port->dev, + "%s - failed to enable flow control: %d\n", + __func__, r); + tty->termios.c_cflag &= ~CRTSCTS; + } + } else { + r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG, + CH341_REG_FLOW_CTL | + ((u16)CH341_REG_FLOW_CTL << 8), + CH341_FLOW_CTL_NONE); + if (r < 0) { + dev_err(&port->dev, + "%s - failed to disable flow control: %d\n", + __func__, r); + tty->termios.c_cflag |= CRTSCTS; + } + } +} + /* Old_termios contains the original termios settings and * tty->termios contains the new setting to be used. */ @@ -546,6 +585,8 @@ static void ch341_set_termios(struct tty_struct *tty, spin_unlock_irqrestore(&priv->lock, flags); ch341_set_handshake(port->serial->dev, priv->mcr); + + ch341_set_flow_control(tty, port, old_termios); } /* -- 2.46.0
