This adds support for enabling and disabling RTS/CTS hardware flow control. Tested using CH341A and CH340E. Fixes part of the following bug report: Link: https://bugzilla.kernel.org/show_bug.cgi?id=197109 Signed-off-by: Lode Willems <me@xxxxxxxxxxxxxxx> --- Changes in v2: - Change the CH341_FLOW_CTL_* values to be 8 bits wide - Set flow control setting unconditionally - Prepare parameters and do one control request - Drop the error message drivers/usb/serial/ch341.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c index d10e4c4848a0..c255a8437e4a 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 0x00 +#define CH341_FLOW_CTL_RTSCTS 0x01 + #define CH341_QUIRK_LIMITED_PRESCALER BIT(0) #define CH341_QUIRK_SIMULATE_BREAK BIT(1) @@ -478,6 +482,28 @@ 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; + u16 flow_ctl; + + if (C_CRTSCTS(tty)) + flow_ctl = ((u16)CH341_FLOW_CTL_RTSCTS << 8) | CH341_FLOW_CTL_RTSCTS; + else + flow_ctl = ((u16)CH341_FLOW_CTL_NONE << 8) | CH341_FLOW_CTL_NONE; + + r = ch341_control_out(port->serial->dev, + CH341_REQ_WRITE_REG, + ((u16)CH341_REG_FLOW_CTL << 8) | CH341_REG_FLOW_CTL, + flow_ctl); + if (r < 0 && old_termios) { + tty->termios.c_cflag &= ~CRTSCTS; + tty->termios.c_cflag |= (old_termios->c_cflag & CRTSCTS); + } +} + /* Old_termios contains the original termios settings and * tty->termios contains the new setting to be used. */ @@ -546,6 +572,8 @@ 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); } /* -- 2.47.1
