[PATCH] Add support for USB Keyboard attached to UHCI

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Aaron Young wrote:
>> On Mon, 26 Nov 2007 13:39:41 -0800 (PST)
>> Aaron Young <ayoung at cthulhu.engr.sgi.com> wrote:
>>>  Konstantin, some comments:
>>> 3. Why can't you use the HID URB? Locking? Using the HID URB seems
>>>    to work fine for OHCI and EHCI. This is the reason that
>>>    seems to cause so much complication in your code. Back
>>>    in the 2.4 timeframe, Intel did a UHCI KDB implementation
>>>    that used the HID URB. Perhaps it would be  useful to dig up that
>>>    old code and compare it? I can possibly pass that code on to you
>>>    if you want...
>>>    Also, does enqueing two URBs for the same device cause any
>>> problems (is it "legal")? 
>>>  -Aaron
>>   I explained it earlier:
>>   http://oss.sgi.com/archives/kdb/2007-11/msg00003.html
>>   KDB Poll driver should not depend on USB kernel code because (in case
>> when KDB driver uses the same code with kernel USB driver) if CPU0
>> executes kernel USB driver and, in the same time, CPU1 hits breakpoint,
>> CPU0 would be frozen in kernel USB driver. USB spinlocks would be
>> locked by CPU0, so KDB USB code couldn't get lock and deadlock would
>> occur. Or, if we don't use lock, kernel USB driver data can't be
>> corrupted.
>   Yes - you're right - it's *possible* to get into kdb while locks are
>   held which, if timed just perfectly, could result in kdb crashing trying
>   to walk lists, etc. This is also true of EHCI and OHCI (I think).
>   I've never seen it happen, but it could in theory...
>   I'm not sure it's worth it to rewrite all this code to cover this possibility,
>   so what I might consider doing is just to check for the critical locks being 
>   held out of the poll functions and if so, give an error and punt 
>   (return -1) - i.e. the keyboard(s) for
>   that HC will not be useable in this case. Much easier
>   and probably sufficient for a debugger IMO. 
>   Jay, prepare for another patch for this! ;-)
>   -Aaron
  Aaron, I'm little bit confused . Are you going to integrate my UHCI 
code to KDB?

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