[PATCH v4] USB: serial: xr: Add TIOCGRS485 and TIOCSRS485 ioctls

Jarkko Sonninen
2023-04-23T19:00:11Z

Exar devices like XR21B1411 can control an RS485 transceiver by
automatically asserting the RTS#/RS485 pin before sending data
and deasserting it when the last stop bit has been transmitted.
The polarity of the RST#/RS485 signal is configurable and the
hardware also supports half-duplex turn-around delay and
address matching mode.

Add support for enabling and disabling RS-485 mode and
configuring the RST#/RS485 signal polarity using the TIOCGRS485
and TIOCSRS485 ioctls. Support for half-duplex turn-around delay
and address matching mode are left unimplemented for now.

User enables RS-485 mode by setting SER_RS485_ENABLED flag in
struct serial_rs485 flags. User should also set either
SER_RS485_RTS_ON_SEND or SER_RS485_RTS_AFTER_SEND to select the
behaviour of the RTS#/RS485 pin. Setting SER_RS485_RTS_ON_SEND
will drive RTS#/RS485 high during transmission. As this is the
typical application described by Exar, it is selected when
user sets neither or both flags.

Signed-off-by: Jarkko Sonninen <kasper@iki.fi>
---
Changes in v3:
- In this version only rs485.flags are stored to state.
- There is no locking as only one bit of the flags is used.
- ioctl returns -ENOIOCTLCMD as the actual error handling is in tty code.
Changes in v4:
- Store struct rs485 to data
- Add mutex to protect data->rs485.
- Implement SER_RS485_RTS_ON_SEND or SER_RS485_RTS_AFTER_SEND flags
- SER_RS485_RTS_ON_SEND is the default like in serial_core.c

drivers/usb/serial/xr_serial.c | 93 +++++++++++++++++++++++++++++++++-
1 file changed, 92 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
index fdb0aae546c3..a2157619b63c 100644
--- a/drivers/usb/serial/xr_serial.c
+++ b/drivers/usb/serial/xr_serial.c
@@ -19,6 +19,7 @@
#include <linux/usb.h>
#include <linux/usb/cdc.h>
#include <linux/usb/serial.h>
+#include <linux/mutex.h>

struct xr_txrx_clk_mask {
u16 tx;
@@ -93,6 +94,7 @@ struct xr_txrx_clk_mask {
#define XR_GPIO_MODE_SEL_DTR_DSR 0x2
#define XR_GPIO_MODE_SEL_RS485 0x3
#define XR_GPIO_MODE_SEL_RS485_ADDR 0x4
+#define XR_GPIO_MODE_RS485_TX_H 0x8
#define XR_GPIO_MODE_TX_TOGGLE 0x100
#define XR_GPIO_MODE_RX_TOGGLE 0x200

@@ -237,6 +239,8 @@ static const struct xr_type xr_types[] = {
struct xr_data {
const struct xr_type *type;
u8 channel; /* zero-based index or interface number */
+ struct serial_rs485 rs485;
+ struct mutex lock;
};

static int xr_set_reg(struct usb_serial_port *port, u8 channel, u16 reg, u16 val)
@@ -630,6 +634,7 @@ static void xr_set_flow_mode(struct tty_struct *tty,
const struct xr_type *type = data->type;
u16 flow, gpio_mode;
int ret;
+ bool rs485_enabled;

ret = xr_get_reg_uart(port, type->gpio_mode, &gpio_mode);
if (ret)
@@ -645,7 +650,17 @@ static void xr_set_flow_mode(struct tty_struct *tty,
/* Set GPIO mode for controlling the pins manually by default. */
gpio_mode &= ~XR_GPIO_MODE_SEL_MASK;

- if (C_CRTSCTS(tty) && C_BAUD(tty) != B0) {
+ rs485_enabled = !!(data->rs485.flags & SER_RS485_ENABLED);
+ if (rs485_enabled) {
+ dev_dbg(&port->dev, "Enabling RS-485\n");
+ gpio_mode |= XR_GPIO_MODE_SEL_RS485;
+ if (data->rs485.flags & SER_RS485_RTS_ON_SEND)
+ gpio_mode |= XR_GPIO_MODE_RS485_TX_H;
+ else
+ gpio_mode &= ~XR_GPIO_MODE_RS485_TX_H;
+ }
+
+ if (C_CRTSCTS(tty) && C_BAUD(tty) != B0 && !rs485_enabled) {
dev_dbg(&port->dev, "Enabling hardware flow ctrl\n");
gpio_mode |= XR_GPIO_MODE_SEL_RTS_CTS;
flow = XR_UART_FLOW_MODE_HW;
@@ -809,6 +824,80 @@ static void xr_cdc_set_line_coding(struct tty_struct *tty,
kfree(lc);
}

+static void xr_sanitize_serial_rs485(struct serial_rs485 *rs485)
+{
+ if (!(rs485->flags & SER_RS485_ENABLED)) {
+ memset(rs485, 0, sizeof(*rs485));
+ return;
+ }
+
+ /* Select RTS on send if the user hasn't selected the mode properly */
+ if (!!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
+ !!(rs485->flags & SER_RS485_RTS_AFTER_SEND)) {
+ rs485->flags |= SER_RS485_RTS_ON_SEND;
+ rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
+ }
+
+ /* Only the flags are implemented at the moment */
+ rs485->flags &= SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND |
+ SER_RS485_RTS_AFTER_SEND;
+ rs485->delay_rts_before_send = 0;
+ rs485->delay_rts_after_send = 0;
+ memset(rs485->padding, 0, sizeof(rs485->padding));
+}
+
+static int xr_get_rs485_config(struct tty_struct *tty,
+ struct serial_rs485 *argp)
+{
+ struct usb_serial_port *port = tty->driver_data;
+ struct xr_data *data = usb_get_serial_port_data(port);
+
+ mutex_lock(&data->lock);
+ if (copy_to_user(argp, &data->rs485, sizeof(data->rs485))) {
+ mutex_unlock(&data->lock);
+ return -EFAULT;
+ }
+ mutex_unlock(&data->lock);
+
+ return 0;
+}
+
+static int xr_set_rs485_config(struct tty_struct *tty,
+ struct serial_rs485 *argp)
+{
+ struct usb_serial_port *port = tty->driver_data;
+ struct xr_data *data = usb_get_serial_port_data(port);
+ struct serial_rs485 rs485;
+
+ if (copy_from_user(&rs485, argp, sizeof(rs485)))
+ return -EFAULT;
+ xr_sanitize_serial_rs485(&rs485);
+
+ mutex_lock(&data->lock);
+ data->rs485 = rs485;
+ xr_set_flow_mode(tty, port, NULL);
+ mutex_unlock(&data->lock);
+
+ if (copy_to_user(argp, &rs485, sizeof(rs485)))
+ return -EFAULT;
+
+ return 0;
+}
+
+static int xr_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
+{
+ void __user *argp = (void __user *)arg;
+
+ switch (cmd) {
+ case TIOCGRS485:
+ return xr_get_rs485_config(tty, argp);
+ case TIOCSRS485:
+ return xr_set_rs485_config(tty, argp);
+ }
+
+ return -ENOIOCTLCMD;
+}
+
static void xr_set_termios(struct tty_struct *tty,
struct usb_serial_port *port,
const struct ktermios *old_termios)
@@ -939,6 +1028,7 @@ static int xr_port_probe(struct usb_serial_port *port)
return -ENOMEM;

data->type = type;
+ mutex_init(&data->lock);

desc = &port->serial->interface->cur_altsetting->desc;
if (type_id == XR21V141X)
@@ -1010,6 +1100,7 @@ static struct usb_serial_driver xr_device = {
.set_termios = xr_set_termios,
.tiocmget = xr_tiocmget,
.tiocmset = xr_tiocmset,
+ .ioctl = xr_ioctl,
.dtr_rts = xr_dtr_rts
};

--
2.34.1