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USB: serial: ch341: add hardware flow control RTS/CTS

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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@lodewillems.com>
[ johan: prepare index argument once, drop casts ]
Signed-off-by: Johan Hovold <johan@kernel.org>
This commit is contained in:
Lode Willems
2024-12-18 18:25:05 +01:00
committed by Johan Hovold
parent 4bbf9020be
commit 35478bc369
1 changed files with 28 additions and 0 deletions
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drivers/usb/serial/ch341.c
+28
View File
@@ -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 @@ err_kill_interrupt_urb:
return r;
}
static void ch341_set_flow_control(struct tty_struct *tty,
struct usb_serial_port *port,
const struct ktermios *old_termios)
{
u16 flow_ctl;
int r;
if (C_CRTSCTS(tty))
flow_ctl = CH341_FLOW_CTL_RTSCTS;
else
flow_ctl = CH341_FLOW_CTL_NONE;
r = ch341_control_out(port->serial->dev,
CH341_REQ_WRITE_REG,
(CH341_REG_FLOW_CTL << 8) | CH341_REG_FLOW_CTL,
(flow_ctl << 8) | 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);
}
/*