[PATCH 6.18 147/198] USB: cdc-acm: Add quirks for Yoga Book 9 14IAH10 INGENIC touchscreen

Greg Kroah-Hartman
2026-04-20T16:04:55Z

From: Dave Carey <carvsdriver@gmail.com>

commit f58752ebcb35e156c85cd1a82d6579c7af3b9023 upstream.

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>
Cc: stable <stable@kernel.org>
Tested-by: Dave Carey <carvsdriver@gmail.com>
Acked-by: Oliver Neukum <oneukum@suse.com>
Link: https://patch.msgid.link/20260402182950.389016-1-carvsdriver@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/class/cdc-acm.c | 53 ++++++++++++++++++++++++++++++++++++++------
1 file changed, 46 insertions(+), 7 deletions(-)

--- 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 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_
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

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)
@@ -1328,6 +1340,9 @@ skip_normal_probe:
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;
}
@@ -1522,6 +1537,9 @@ skip_countries:
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)
@@ -1543,6 +1561,13 @@ skip_countries:

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:
@@ -1669,7 +1694,7 @@ static int acm_resume(struct usb_interfa

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 (;;) {
@@ -2016,6 +2041,20 @@ static const struct usb_device_id acm_id
/* 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) },