A subset of CH341 devices does not support all features, namely the
prescaler is limited to a reduced precision and there is no support for
sending a RS232 break condition.
These devices can usually be identified by an imprint of "340" on the
turquoise-colored plug. They're called "HL340" in this driver.
Signed-off-by: Michael Hanselmann <public@xxxxxxxxx>
---
drivers/usb/serial/ch341.c | 42 ++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 518209072c50..0523f46f53c7 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -89,6 +89,7 @@ struct ch341_private {
u8 mcr;
u8 msr;
u8 lcr;
+ u8 flags;
};
static void ch341_set_termios(struct tty_struct *tty,
@@ -315,6 +316,43 @@ out: kfree(buffer);
return r;
}
+/*
+ * A subset of CH341 devices, called "HL340" in this driver, does not support
+ * all features. The prescaler is limited and there is no support for sending
+ * a RS232 break condition. A read failure when trying to set up the latter is
+ * used to detect these devices.
+ */
+static int ch341_detect_hl340(struct usb_device *dev)
+{
+ const unsigned int size = 2;
+ char *buffer;
+ int r;
+
+ buffer = kmalloc(size, GFP_KERNEL);
+ if (!buffer)
+ return -ENOMEM;
+
+ r = ch341_control_in(dev, CH341_REQ_READ_REG,
+ CH341_REG_BREAK, 0, buffer, size);
+ if (r == -EPIPE) {
+ dev_dbg(&dev->dev, "%s - Chip is a HL340 variant\n",
+ __func__);
+ r = 1;
+ goto out;
+ }
+
+ if (r < 0) {
+ dev_err(&dev->dev, "%s - USB control read error (%d)\n",
+ __func__, r);
+ goto out;
+ }
+
+ r = 0;
+
+out: kfree(buffer);
+ return r;
+}
+
static int ch341_port_probe(struct usb_serial_port *port)
{
struct ch341_private *priv;
@@ -336,6 +374,10 @@ static int ch341_port_probe(struct usb_serial_port *port)
if (r < 0)
goto error;
+ r = ch341_detect_hl340(port->serial->dev);
+ if (r < 0)
+ goto error;
+
usb_set_serial_port_data(port, priv);
return 0;
--
2.20.1
