Re: [PATCH v2] usb: dwc3: gadget: check that event count does not exceed event buffer length

[Frode Isaksen <fisaksen@baylibre.com>]

On 4/2/25 6:42 AM, Krishna Kurapati wrote:
>> I still wonder what's current behavior of the HW to properly respond
>> here. If the device is dead, register read often returns all Fs, which
>> may be the case you're seeing here. If so, we should properly prevent
>> the driver from accessing the device and properly teardown the driver.
>>
>> If this is a momentary bleep/lost of power in the device, perhaps your
>> change here is sufficient and the driver can continue to access the
>> device.
>>
>> With the difficulty of reproducing this issue, can you confirm that the
>> device still operates properly after this change?
>
> Unfortunately, I did not test this particular change of returning when 
> ev count is invalid. I stress tested the change of copying only 4K 
> [1], but didn't see any issue. I suspect we didn't hit the issue later 
> again in the course of 14 day testing.
>
> [1]: 
> https://lore.kernel.org/all/20230521100330.22478-1-quic_kriskura@quicinc.com/ 
>
>
> Regards,
> Krishna,
>
I have been running my fix for over a year with millions of Quest 3 
devices, and no strange bugs caused by this has been seen. Without the 
fix, there were 1 to 2 crashes per week.

So I think it's safe to just return with IRQ_NONE when the count exceeds 
the event length.

Thanks,

Frode