Re: i.MX kernel hangup caused by chipidea USB gadget driver

John Ernberg
2025-06-10T15:03:32Z

Hi Shawn,

On 6/10/25 5:04 AM, Shawn Guo wrote:
> 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@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
>

Perhaps the hanging point is different in i.MX8MM, I unfortunately do
not have any boards with that SoC on them. When I tracked down the
problem on QXP I threw similar BUG_ON statements in most while loops.

But since a fix is very likely identified already by you I'm not sure in
the value of finding the exact spot.

Best regards // John Ernberg