Fix error 32 returned by CP210X_SET_MHS when hardware flow control is enabled.
The root cause of error 32 is that user application (CoolTerm, linux-serial-test)
opened cp210x device with hardware flow control then attempt to control RTS/DTR pins.
In hardware flow control, RTS/DTR pins will be controlled by hardware only,
any attempt to control those pins will cause error 32 from the device.
This fix will block MHS command(command to control RTS/DTR pins) to the device
if hardware flow control is being used.
Signed-off-by: Pho Tran <pho.tran@xxxxxxxxxx>
---
01/21/2021: Patch v3 modified based on comment from Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
01/19/2021: Patch v2 Modified based on comment from Johan Hovold <johan@xxxxxxxxxx>
and Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/serial/cp210x.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index fbb10dfc56e3..814dff5fee98 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -1204,7 +1204,12 @@ static int cp210x_tiocmset(struct tty_struct *tty,
unsigned int set, unsigned int clear)
{
struct usb_serial_port *port = tty->driver_data;
- return cp210x_tiocmset_port(port, set, clear);
+
+ /* Don't send SET_MHS command if device in hardware flow control mode. */
+ if (C_CRTSCTS(tty))
+ return 0;
+ else
+ return cp210x_tiocmset_port(port, set, clear);
}
static int cp210x_tiocmset_port(struct usb_serial_port *port,
--
2.17.1
