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USB: serial: ch341: add basis for quirk detection

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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>
This commit is contained in:
Michael Hanselmann 2020-03-31 23:37:18 +00:00 committed by Johan Hovold
parent 986c1748c8
commit c404bf4aa9
1 changed files with 53 additions and 0 deletions
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53
drivers/usb/serial/ch341.c
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@ -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_serial_port *port)
goto error;
usb_set_serial_port_data(port, priv);
r = ch341_detect_quirks(port);
if (r < 0)
goto error;
return 0;
error: kfree(priv);