A subset of all CH341 devices don't support a real break condition. This
fact is already used in the "ch341_detect_quirks" function. With this
change a quirk is implemented to simulate a break condition by
temporarily lowering the baud rate and sending a NUL byte.
The primary drawback of this approach is that the duration of the break
can't be controlled by userland.
The "TTY_DRIVER_HARDWARE_BREAK" serial driver flag was investigated as
an alternative. It's a driver-wide flag and would've required
significant changes to the serial and USB-serial driver frameworks to
expose it for individual USB-serial adapters.
Tested by sending a break condition and watching the TX pin using an
oscilloscope.
Signed-off-by: Michael Hanselmann <public@xxxxxxxxx>
---
drivers/usb/serial/ch341.c | 95 ++++++++++++++++++++++++++++++++++----
1 file changed, 85 insertions(+), 10 deletions(-)
diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index c820772e6a07..fc8ef816d143 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -25,6 +25,7 @@
#define DEFAULT_TIMEOUT 1000
#define CH341_QUIRK_LIMITED_PRESCALER 0x01
+#define CH341_QUIRK_SIMULATE_BREAK 0x02
/* flags for IO-Bits */
#define CH341_BIT_RTS (1 << 6)
@@ -94,6 +95,7 @@ struct ch341_private {
u8 msr;
u8 lcr;
u8 quirks;
+ unsigned long break_end;
};
static void ch341_set_termios(struct tty_struct *tty,
@@ -203,14 +205,11 @@ static int ch341_calc_divisor(speed_t speed, unsigned int ps,
* 2 <= div <= 256 if fact = 0, or
* 9 <= div <= 256 if fact = 1
*/
-static int ch341_get_divisor(struct ch341_private *priv)
+static int ch341_get_divisor(struct ch341_private *priv, speed_t speed)
{
- speed_t speed;
unsigned int fact, div, clk_div;
int ps;
- speed = priv->baud_rate;
-
/*
* Clamp to supported range, making the later range sanity checks
* redundant.
@@ -282,15 +281,16 @@ static int ch341_get_divisor(struct ch341_private *priv)
}
static int ch341_set_baudrate_lcr(struct usb_device *dev,
- struct ch341_private *priv, u8 lcr)
+ struct ch341_private *priv,
+ unsigned baud_rate, u8 lcr)
{
int val;
int r;
- if (!priv->baud_rate)
+ if (!baud_rate)
return -EINVAL;
- val = ch341_get_divisor(priv);
+ val = ch341_get_divisor(priv, baud_rate);
if (val < 0)
return -EINVAL;
@@ -369,7 +369,7 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
if (r < 0)
goto out;
- r = ch341_set_baudrate_lcr(dev, priv, priv->lcr);
+ r = ch341_set_baudrate_lcr(dev, priv, priv->baud_rate, priv->lcr);
if (r < 0)
goto out;
@@ -401,7 +401,7 @@ static int ch341_detect_quirks(struct usb_device *dev)
if (r == -EPIPE) {
dev_dbg(&dev->dev, "%s - reading break condition register"
" failed (%d)\n", __func__, r);
- r = CH341_QUIRK_LIMITED_PRESCALER;
+ r = CH341_QUIRK_LIMITED_PRESCALER | CH341_QUIRK_SIMULATE_BREAK;
goto out;
}
@@ -579,7 +579,8 @@ static void ch341_set_termios(struct tty_struct *tty,
if (baud_rate) {
priv->baud_rate = baud_rate;
- r = ch341_set_baudrate_lcr(port->serial->dev, priv, lcr);
+ r = ch341_set_baudrate_lcr(port->serial->dev, priv,
+ priv->baud_rate, lcr);
if (r < 0 && old_termios) {
priv->baud_rate = tty_termios_baud_rate(old_termios);
tty_termios_copy_hw(&tty->termios, old_termios);
@@ -598,15 +599,89 @@ static void ch341_set_termios(struct tty_struct *tty,
ch341_set_handshake(port->serial->dev, priv->mcr);
}
+/*
+ * A subset of all CH34x devices don't support a real break condition and
+ * reading CH341_REG_BREAK fails (see also ch341_detect_quirks). This function
+ * simulates a break condition by lowering the baud rate to the minimum
+ * supported by the hardware upon enabling the break condition and sending
+ * a NUL byte.
+ *
+ * Normally the duration of the break condition can be controlled individually
+ * by userspace using TIOCSBRK and TIOCCBRK or by passing an argument to
+ * TCSBRKP. Due to how the simulation is implemented the duration can't be
+ * controlled. The duration is always 1s / 46bd * 10bit = 217ms.
+ */
+static void ch341_simulate_break(struct tty_struct *tty, int break_state)
+{
+ struct usb_serial_port *port = tty->driver_data;
+ struct ch341_private *priv = usb_get_serial_port_data(port);
+ unsigned long delay;
+ int r;
+
+ if (break_state != 0) {
+ dev_dbg(&port->dev, "%s - Enter break state requested\n",
+ __func__);
+
+ r = ch341_set_baudrate_lcr(port->serial->dev, priv,
+ CH341_MIN_BPS,
+ CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX |
+ CH341_LCR_CS8);
+ if (r < 0) {
+ dev_err(&port->dev, "%s - baud rate status %d\n",
+ __func__, r);
+ goto restore;
+ }
+
+ r = tty_put_char(tty, '\0');
+ if (r < 0) {
+ dev_err(&port->dev, "%s - write status %d\n",
+ __func__, r);
+ goto restore;
+ }
+
+ priv->break_end = jiffies + (10 * HZ / CH341_MIN_BPS);
+
+ return;
+ }
+
+ dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__);
+
+ if (time_before(jiffies, priv->break_end)) {
+ /* Wait until NUL byte is written */
+ delay = min_t(unsigned long, HZ, priv->break_end - jiffies);
+
+ dev_dbg(&port->dev, "%s - sleep for %d ms\n", __func__,
+ jiffies_to_msecs(delay));
+ schedule_timeout_interruptible(delay);
+ }
+
+restore:
+ /* Restore original baud rate */
+ r = ch341_set_baudrate_lcr(port->serial->dev, priv, priv->baud_rate,
+ priv->lcr);
+ if (r < 0)
+ dev_err(&port->dev, "%s - baud rate status %d\n", __func__, r);
+}
+
static void ch341_break_ctl(struct tty_struct *tty, int break_state)
{
const uint16_t ch341_break_reg =
((uint16_t) CH341_REG_LCR << 8) | CH341_REG_BREAK;
struct usb_serial_port *port = tty->driver_data;
+ struct ch341_private *priv = usb_get_serial_port_data(port);
int r;
uint16_t reg_contents;
uint8_t *break_reg;
+ if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) {
+ dev_warn_once(&port->dev,
+ "%s - hardware doesn't support real break"
+ " condition, simulating instead\n",
+ __func__);
+ ch341_simulate_break(tty, break_state);
+ return;
+ }
+
break_reg = kmalloc(2, GFP_KERNEL);
if (!break_reg)
return;
--
2.20.1
