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. This patch adds a detection function
which will be extended to return quirk flags as they're implemented.
The author's affected device has an imprint of "340" on the
turquoise-colored plug, but not all such devices appear to be affected.
Signed-off-by: Michael Hanselmann <public@xxxxxxxxx>
---
drivers/usb/serial/ch341.c | 49 ++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)
diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 85e7125d0194..9c839f67c3d4 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -87,6 +87,7 @@ struct ch341_private {
u8 mcr;
u8 msr;
u8 lcr;
+ u8 quirks;
};
static void ch341_set_termios(struct tty_struct *tty,
@@ -330,6 +331,45 @@ out: kfree(buffer);
return r;
}
+static int ch341_detect_quirks(struct usb_device *dev)
+{
+ const unsigned int size = 2;
+ char *buffer;
+ int r;
+
+ buffer = kmalloc(size, GFP_KERNEL);
+ if (!buffer)
+ return -ENOMEM;
+
+ /*
+ * A subset of CH34x devices 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.
+ */
+ r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), CH341_REQ_READ_REG,
+ USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
+ CH341_REG_BREAK, 0, buffer, size, DEFAULT_TIMEOUT);
+ if (r == -EPIPE) {
+ dev_dbg(&dev->dev, "%s - reading break condition register"
+ " failed (%d)\n", __func__, r);
+ r = 0;
+ 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;
@@ -351,6 +391,15 @@ static int ch341_port_probe(struct usb_serial_port *port)
if (r < 0)
goto error;
+ r = ch341_detect_quirks(port->serial->dev);
+ if (r < 0)
+ goto error;
+ if (r != 0) {
+ dev_dbg(&port->serial->dev->dev,
+ "%s - enabling quirks flags %08x\n", __func__, r);
+ priv->quirks |= r;
+ }
+
usb_set_serial_port_data(port, priv);
return 0;
--
2.20.1
