Re: [Bluez-users] error on connect

[Marco Trudel <mtrudel@gmx.ch>]

Hello Marcel

Do I get this right:
- The ACL packet that cause the problem is sent before the connection is 
etablished. This is ok and defined in the specification.
- The received dongle is responsible to keep this packet back until the 
connection is etablished and process them then.
- the csr dongles seem to handle this correct.
- the broadcom dongle seem to don't handle this correct. they probably 
suffer a race condition. so they may work or may not work.


regards
Marco


Marcel Holtmann wrote:
> Hi Marco,
> 
> 
>>>>>>It looks like this too early packet now causes the (sensefull) 
>>>>>>"hci_acldata_packet: hci1 ACL packet for unknown connection handle 6" 
>>>>>>kernel error message. The dongle then waits for this acl package and thinks 
>>>>>>this connection is in etablishing phase, so it is blocked.
>>>>>
>>>>>>>From a quick look at the kernel code, it seems that an ACL packet for an
>>>>>unknown connection handle may corrupt the HCI flow control.
>>>>
>>>>I think exactly this happens...
>>>
>>>However even if I fix the HCI flow control problem, the packet is still
>>>lost, because we don't know the connection handle at that time.
>>
>>yes, thats what seems strainge: why is this ACL packet sent that early?
>>that doesn't make sense for me (but I din't develop bluetooth)...
>>In my opinion, it should be sent after the connection is etablished.
> 
> 
> It is not only your opinion. The specification defines it this way. This
> is simply a race condition inside the link manager.



>>>>>>The question now is, who is responsible for holding this packed back? The 
>>>>>>kernel? The dongle itself?
>>>>>
>>>>>The dongle is responsible for that and actually it is only allowed to
>>>>>send data packets after the "Connect Complete" event. Otherwise we don't
>>>>>know its handle and thus can't correctly assign it to a connection.



>>>>but then it's strainge that these ACL packets are always sent before the 
>>>>"connection" successfull packet. or do I right now miss something?
>>>
>>>This must be a bug in the Broadcom link manager firmware. Seems like
>>>BlueZ is "too fast" for these chips.
>>>
>>>If you wanna workaround this problem you must put potential ACL data
>>>packets into a queue and then check this queue after you received the
>>>connection handle.
>>
>>that's pretty ugly. Maybe there's another solution for this. I think 
>>that the problem isnt yet fully understood.
> 
> 
> The problem is clear. The Broadcom link manager has a race condition
> here. It should queue the package until they send the connect complete
> event.
> 
> 
>> > You only saw that on the listing side, right?
>>
>>what do you mean with this?
>>on the sending side - if i remember right - the acl packet is alway sent 
>>before the connection is successfull etablished. I'll check again...
> 
> 
> Please do so, but there should be no problem. We only send any data to
> the chip after we received the connect complete. All previous packages
> are queued.
> 
> Regards
> 
> Marcel
> 
> 
> 
> 
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