Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability

From: Lu Baolu
Date: Thu Jan 26 2017 - 02:49:36 EST

Hi Ingo,

On 01/26/2017 03:19 PM, Ingo Molnar wrote:
> * Lu Baolu <> wrote:
>> Fair enough.
>> USB connection is stable enough, unless the user unplugs the
>> USB cable during debugging.
> What does the hardware do in this case? The XHCI registers are in the host
> hardware, so they won't disappear, right? Is there some cable connection status
> bit we can extract without interrupts?

Yes, there are register bits for us to know the cable status. I will go
through the spec again and give you more accurate answer later.

I'm sorry. I will be off during the next 7 days for Chinese New Year
holiday. My email access will be very limited during this time. I will
revisit this thread after I am back from holiday.

Sorry for the inconvenience.

Best regards,
Lu Baolu

> I.e. if there's any polling component then it would be reasonable to add an error
> component: poll the status and if it goes 'disconnected' then disable early-printk
> altogether in this case and trigger an emergency printk() so that there's chance
> that the user notices [if the system does not misbehave otherwise].
> I.e. try to be as robust and informative as lockdep - yet don't lock up the host
> kernel: lockdep too is called from very deep internals, there are various
> conditions where it sees corrupt data structures (i.e. a 'disconnect' - a system
> environment outside the normal bounds of operation), yet of the kernel and over
> the last 10+ years of lockdep's existence we had very, very few cases of lockdep
> itself locking up and behaving unpredictably.
> Thanks,
> Ingo