[PATCH] USB: cdc-acm: Add quirks for Yoga Book 9 14IAH10 INGENIC touchscreen

[Dave Carey <carvsdriver@gmail.com>]

The Lenovo Yoga Book 9 14IAH10 (83KJ) has a composite USB device
(17EF:6161) that controls both touchscreens via a CDC ACM interface.
Interface 0 is a standard CDC ACM control interface, but interface 1
(the data interface) incorrectly declares vendor-specific class (0xFF)
instead of USB_CLASS_CDC_DATA. cdc-acm rejects the device at probe with
-EINVAL, leaving interface 0 unbound and EP 0x82 never polled.

With no consumer polling EP 0x82, the firmware's watchdog fires every
~20 seconds and resets the USB bus, producing a continuous disconnect/
reconnect loop that prevents the touchscreens from ever initialising.

Add two new quirk flags:

VENDOR_CLASS_DATA_IFACE: Bypasses the bInterfaceClass check in
acm_probe() that would otherwise reject the vendor-class data
interface with -EINVAL.

ALWAYS_POLL_CTRL: Submits the notification URB at probe() rather than
waiting for a TTY open. This keeps EP 0x82 polled at all times,
permanently suppressing the firmware watchdog. The URB is resubmitted
after port_shutdown() and on system resume. SET_CONTROL_LINE_STATE
(DTR|RTS) is sent at probe and after port_shutdown() to complete
firmware handshake.

Note: the firmware performs exactly 4 USB connect/disconnect cycles
(~19 s each) on every cold boot before stabilising. This is a fixed
firmware property; touch is available ~75-80 s after power-on.

Signed-off-by: Dave Carey <carvsdriver@gmail.com>
Tested-by: Dave Carey <carvsdriver@gmail.com>
---
 drivers/usb/class/cdc-acm.c | 53 ++++++++++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 7ede29d4c..568f0c479 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -114,6 +114,8 @@ static int acm_ctrl_msg(struct acm *acm, int request, int value,
 	int retval;
 
 	retval = usb_autopm_get_interface(acm->control);
+#define VENDOR_CLASS_DATA_IFACE		BIT(9)  /* data interface uses vendor-specific class */
+#define ALWAYS_POLL_CTRL		BIT(10) /* keep ctrl URB active even without an open TTY */
 	if (retval)
 		return retval;
 
@@ -710,12 +712,14 @@ static int acm_port_activate(struct tty_port *port, struct tty_struct *tty)
 	set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
 	acm->control->needs_remote_wakeup = 1;
 
-	acm->ctrlurb->dev = acm->dev;
-	retval = usb_submit_urb(acm->ctrlurb, GFP_KERNEL);
-	if (retval) {
-		dev_err(&acm->control->dev,
-			"%s - usb_submit_urb(ctrl irq) failed\n", __func__);
-		goto error_submit_urb;
+	if (!(acm->quirks & ALWAYS_POLL_CTRL)) {
+		acm->ctrlurb->dev = acm->dev;
+		retval = usb_submit_urb(acm->ctrlurb, GFP_KERNEL);
+		if (retval) {
+			dev_err(&acm->control->dev,
+				"%s - usb_submit_urb(ctrl irq) failed\n", __func__);
+			goto error_submit_urb;
+		}
 	}
 
 	acm_tty_set_termios(tty, NULL);
@@ -788,6 +792,14 @@ static void acm_port_shutdown(struct tty_port *port)
 
 	acm_unpoison_urbs(acm);
 
+	if (acm->quirks & ALWAYS_POLL_CTRL) {
+		acm->ctrlurb->dev = acm->dev;
+		if (usb_submit_urb(acm->ctrlurb, GFP_KERNEL))
+			dev_dbg(&acm->control->dev,
+				"ctrl polling restart failed after port close\n");
+		/* port_shutdown() cleared DTR/RTS; restore them */
+		acm_set_control(acm, USB_CDC_CTRL_DTR | USB_CDC_CTRL_RTS);
+	}
 }
 
 static void acm_tty_cleanup(struct tty_struct *tty)
@@ -1322,6 +1334,9 @@ static int acm_probe(struct usb_interface *intf,
 			dev_dbg(&intf->dev,
 				"Your device has switched interfaces.\n");
 			swap(control_interface, data_interface);
+		} else if (quirks & VENDOR_CLASS_DATA_IFACE) {
+			dev_dbg(&intf->dev,
+				"Vendor-specific data interface class, continuing.\n");
 		} else {
 			return -EINVAL;
 		}
@@ -1516,6 +1531,9 @@ static int acm_probe(struct usb_interface *intf,
 	acm->line.bDataBits = 8;
 	acm_set_line(acm, &acm->line);
 
+	if (quirks & ALWAYS_POLL_CTRL)
+		acm_set_control(acm, USB_CDC_CTRL_DTR | USB_CDC_CTRL_RTS);
+
 	if (!acm->combined_interfaces) {
 		rv = usb_driver_claim_interface(&acm_driver, data_interface, acm);
 		if (rv)
@@ -1537,6 +1555,13 @@ static int acm_probe(struct usb_interface *intf,
 
 	dev_info(&intf->dev, "ttyACM%d: USB ACM device\n", minor);
 
+	if (acm->quirks & ALWAYS_POLL_CTRL) {
+		acm->ctrlurb->dev = acm->dev;
+		if (usb_submit_urb(acm->ctrlurb, GFP_KERNEL))
+			dev_warn(&intf->dev,
+				 "failed to start persistent ctrl polling\n");
+	}
+
 	return 0;
 
 err_release_data_interface:
@@ -1663,7 +1688,7 @@ static int acm_resume(struct usb_interface *intf)
 
 	acm_unpoison_urbs(acm);
 
-	if (tty_port_initialized(&acm->port)) {
+	if (tty_port_initialized(&acm->port) || (acm->quirks & ALWAYS_POLL_CTRL)) {
 		rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);
 
 		for (;;) {
@@ -2007,6 +2032,20 @@ static const struct usb_device_id acm_ids[] = {
 	/* CH343 supports CAP_BRK, but doesn't advertise it */
 	{ USB_DEVICE(0x1a86, 0x55d3), .driver_info = MISSING_CAP_BRK, },
 
+	/*
+	 * Lenovo Yoga Book 9 14IAH10 (83KJ) — INGENIC 17EF:6161 touchscreen
+	 * composite device.  The CDC ACM control interface (0) uses a standard
+	 * Union descriptor, but the data interface (1) is declared as vendor-
+	 * specific class (0xff) with no CDC data descriptors, so cdc-acm would
+	 * normally reject it.  The firmware also requires continuous polling of
+	 * the notification endpoint (EP 0x82) to suppress a 20-second watchdog
+	 * reset; ALWAYS_POLL_CTRL keeps the ctrlurb active even when no TTY is
+	 * open.  Match only the control interface by class to avoid probing the
+	 * vendor-specific data interface.
+	 */
+	{ USB_DEVICE_INTERFACE_CLASS(0x17ef, 0x6161, USB_CLASS_COMM),
+	  .driver_info = VENDOR_CLASS_DATA_IFACE | ALWAYS_POLL_CTRL },
+
 	/* control interfaces without any protocol set */
 	{ USB_INTERFACE_INFO(USB_CLASS_COMM, USB_CDC_SUBCLASS_ACM,
 		USB_CDC_PROTO_NONE) },
-- 
2.53.0