i.MX kernel hangup caused by chipidea USB gadget driver

Shawn Guo
2025-06-09T05:31:49Z

Hi Xu, Peter,

I'm seeing a kernel hangup on imx8mm-evk board. It happens when:

- USB gadget is enabled as Ethernet
- There is data transfer over USB Ethernet
- Device is going in/out suspend

A simple way to reproduce the issue could be:

1. Copy a big file (like 500MB) from host PC to device with scp

2. While the file copy is ongoing, suspend & resume the device like:

$ echo +3 > /sys/class/rtc/rtc0/wakealarm; echo mem > /sys/power/state

3. The device will hang up there

I reproduced on the following kernels:

- Mainline kernel
- NXP kernel lf-6.6.y
- NXP kernel lf-6.12.y

But NXP kernel lf-6.1.y doesn't have this problem. I tracked it down to
Peter's commit [1] on lf-6.1.y, and found that the gadget disconnect &
connect calls got lost from suspend & resume hooks, when the commit were
split and pushed upstream. I confirm that adding the calls back fixes
the hangup.

---8<--------------------

diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
index 8a9b31fd5c89..72329a7eac4d 100644
--- a/drivers/usb/chipidea/udc.c
+++ b/drivers/usb/chipidea/udc.c
@@ -2374,6 +2374,9 @@ static void udc_suspend(struct ci_hdrc *ci)
*/
if (hw_read(ci, OP_ENDPTLISTADDR, ~0) == 0)
hw_write(ci, OP_ENDPTLISTADDR, ~0, ~0);
+
+ if (ci->driver && ci->vbus_active && (ci->gadget.state != USB_STATE_SUSPENDED))
+ usb_gadget_disconnect(&ci->gadget);
}

static void udc_resume(struct ci_hdrc *ci, bool power_lost)
@@ -2384,6 +2387,9 @@ static void udc_resume(struct ci_hdrc *ci, bool power_lost)
OTGSC_BSVIS | OTGSC_BSVIE);
if (ci->vbus_active)
usb_gadget_vbus_disconnect(&ci->gadget);
+ } else {
+ if (ci->driver && ci->vbus_active)
+ usb_gadget_connect(&ci->gadget);
}

/* Restore value 0 if it was set for power lost check */

---->8------------------

But it's unclear to me why the hangup happens and how the change above
fix the problem. Do you guys have any insight here?

Shawn

[1] https://github.com/reMarkable/linux-imx/commit/0791d25578cb0e46fd93ae7a3c36ff7a424f3547