[PATCH 5.7 04/24] USB: serial: ch341: add basis for quirk detection

Greg Kroah-Hartman
2020-06-09T17:56:39Z

From: Michael Hanselmann <public@hansmi.ch>

commit c404bf4aa9236cb4d1068e499ae42acf48a6ff97 upstream.

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 set 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@hansmi.ch>
Link: https://lore.kernel.org/r/1e1ae0da6082bb528a44ef323d4e1d3733d38858.1585697281.git.public@hansmi.ch
[ johan: use long type for quirks; rephrase and use port device for
messages; handle short reads; set quirk flags directly in
helper function ]
Cc: stable <stable@vger.kernel.org> # 5.5
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/serial/ch341.c | 53 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)

--- 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;
+ unsigned long quirks;
};

static void ch341_set_termios(struct tty_struct *tty,
@@ -308,6 +309,53 @@ out: kfree(buffer);
return r;
}

+static int ch341_detect_quirks(struct usb_serial_port *port)
+{
+ struct ch341_private *priv = usb_get_serial_port_data(port);
+ struct usb_device *udev = port->serial->dev;
+ const unsigned int size = 2;
+ unsigned long quirks = 0;
+ 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(udev, usb_rcvctrlpipe(udev, 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(&port->dev, "break control not supported\n");
+ r = 0;
+ goto out;
+ }
+
+ if (r != size) {
+ if (r >= 0)
+ r = -EIO;
+ dev_err(&port->dev, "failed to read break control: %d\n", r);
+ goto out;
+ }
+
+ r = 0;
+out:
+ kfree(buffer);
+
+ if (quirks) {
+ dev_dbg(&port->dev, "enabling quirk flags: 0x%02lx\n", quirks);
+ priv->quirks |= quirks;
+ }
+
+ return r;
+}
+
static int ch341_port_probe(struct usb_serial_port *port)
{
struct ch341_private *priv;
@@ -330,6 +378,11 @@ static int ch341_port_probe(struct usb_s
goto error;

usb_set_serial_port_data(port, priv);
+
+ r = ch341_detect_quirks(port);
+ if (r < 0)
+ goto error;
+
return 0;

error: kfree(priv);