i.MX kernel hangup caused by chipidea USB gadget driver

[Shawn Guo]

Hi John,

On Mon, Jun 09, 2025 at 02:17:30PM +0000, John Ernberg wrote:

<snip>

> We probably ran into the same problem trying to bring onboard 6.12, going
> from 6.1, on iMX8QXP. I managed to trace the hang to EP priming through a
> combination of debug tracing and BUG_ON experiments. See if it starts
> splatin with the below change.
> 
> ----------------->8------------------
> 
> From 092599ab6f9e20412a7ca1eb118dd2be80cd18ff Mon Sep 17 00:00:00 2001
> From: John Ernberg <john.ernberg at actia.se>
> Date: Mon, 5 May 2025 09:09:01 +0200
> Subject: [PATCH] USB: ci: gadget: Panic if priming when gadget off
> 
> ---
>  drivers/usb/chipidea/udc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/chipidea/udc.c b/drivers/usb/chipidea/udc.c
> index 2fea263a5e30..544aa4fa2d1d 100644
> --- a/drivers/usb/chipidea/udc.c
> +++ b/drivers/usb/chipidea/udc.c
> @@ -203,8 +203,10 @@ static int hw_ep_prime(struct ci_hdrc *ci, int num, int dir, int is_ctrl)
>  
>     hw_write(ci, OP_ENDPTPRIME, ~0, BIT(n));
>  
> -   while (hw_read(ci, OP_ENDPTPRIME, BIT(n)))
> +   while (hw_read(ci, OP_ENDPTPRIME, BIT(n))) {
>         cpu_relax();
> +       BUG_ON(dir == TX && !hw_read(ci, OP_ENDPTCTRL + num, ENDPTCTRL_TXE));
> +   }
>     if (is_ctrl && dir == RX && hw_read(ci, OP_ENDPTSETUPSTAT, BIT(num)))
>         return -EAGAIN;
>  
> ----------------->8------------------

Hmm, I just tested the change on i.MX8MM but didn't see the splatting.
Maybe we are running into a slightly different problems?

Shawn