[PATCH] Proper RTS control when buffers fill

Brant Merryman
2019-12-09T19:17:31Z

Enables usb generic functions for throttle/unthrottle to prevent USB data
loss. CP210x hardware disables RTS but leaves CTS when in hardware flow
control mode and port is closed. When re-opening the serial port, if CTS
is enabled, then RTS must be re-enabled inside the driver.

Signed-off-by: Brant Merryman <brant.merryman@silabs.com>
---
drivers/usb/serial/cp210x.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index f5143eedbc48..fd54181e741b 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -272,6 +272,8 @@ static struct usb_serial_driver cp210x_device = {
.break_ctl = cp210x_break_ctl,
.set_termios = cp210x_set_termios,
.tx_empty = cp210x_tx_empty,
+ .throttle = usb_serial_generic_throttle,
+ .unthrottle = usb_serial_generic_unthrottle,
.tiocmget = cp210x_tiocmget,
.tiocmset = cp210x_tiocmset,
.attach = cp210x_attach,
@@ -915,6 +917,7 @@ static void cp210x_get_termios_port(struct usb_serial_port *port,
u32 baud;
u16 bits;
u32 ctl_hs;
+ u32 flow_repl;

cp210x_read_u32_reg(port, CP210X_GET_BAUDRATE, &baud);

@@ -1013,8 +1016,24 @@ static void cp210x_get_termios_port(struct usb_serial_port *port,
cp210x_read_reg_block(port, CP210X_GET_FLOW, &flow_ctl,
sizeof(flow_ctl));
ctl_hs = le32_to_cpu(flow_ctl.ulControlHandshake);
+ flow_repl = le32_to_cpu(flow_ctl.ulFlowReplace);
+ /* CP210x hardware disables RTS but leaves CTS when in hardware
+ * flow control mode and port is closed.
+ * This allows data to flow out, but new data will not come into
+ * the port. When re-opening the port, if CTS is enabled, then RTS
+ * must be re-enabled. in the driver
+ */
if (ctl_hs & CP210X_SERIAL_CTS_HANDSHAKE) {
dev_dbg(dev, "%s - flow control = CRTSCTS\n", __func__);
+ flow_repl &= ~CP210X_SERIAL_RTS_MASK;
+ flow_repl |= CP210X_SERIAL_RTS_SHIFT(
+ CP210X_SERIAL_RTS_FLOW_CTL);
+
+ flow_ctl.ulControlHandshake = cpu_to_le32(ctl_hs);
+ flow_ctl.ulFlowReplace = cpu_to_le32(flow_repl);
+ cp210x_write_reg_block(port, CP210X_SET_FLOW,
+ &flow_ctl, sizeof(flow_ctl));
+
cflag |= CRTSCTS;
} else {
dev_dbg(dev, "%s - flow control = NONE\n", __func__);
--