Re: 2.6.23-rc3, freeze during gadget ether usage

David Brownell wrote:
>> I'm using 2.6.23-rc3 with AT91RM9200 and USB gadget ether. My device is 
>> essentially the same as an AT91RM9200DK.
>>
>> I'm doing a test where I continuously plug and unplug the device from
>> a Windows XP machine. The driver on the Windows side is the MCCI CDC-SAFE
>> driver.
>>
>> After a random number of dis/connections my Linux system freezes. There
>> are no errors or warning logs, and no "oops!". Eventually the watchdog
>> times out and it resets. If I disable the watchdog timer, it will never
>> leave this frozen state.
> 
> If it's like a DK, that means you have both a VBUS-sense irq and
> an external D+ pullup, right?
> 
> Try ignoring the VBUS sensing IRQ and see if that affects anything.

That appears to solve the problem.

I did:

static struct at91_udc_data __initdata srm2_udc_data = {
//  .vbus_pin   = AT91_PIN_PD4,
     .pullup_pin = AT91_PIN_PD5,
};

I tested it for 3 hours and I could not make the system lockup with this 
change. Windows required rebooting many times, the USB host controllers locked 
up, but my kernel kept going.


> Since the controller is dealing with two clock domains (the USB
> domain at 48 MHz, and the CPU bus clock normally at something else),
> there can be glitches with operations which cross clock domains.
> That's easy enough to goof up in hardware -- not enough synch to
> cope with all the little races -- and it's rarely clear how the
> software should try to defend itself..

Sounds painful. I'm still fairly impressed that the Linux kernel is running on 
these microcontrollers at all. So many new issues to worry about like multiple 
clock domains, fine-grained peripheral control, arbitrary GPIO lines, multiple 
power saving modes, etc.


Thank you very much.


regards,

Aras Vaichas

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