Re: bcmdhd: Strange Power Save messages

[Arend Van Spriel <arend.vanspriel@broadcom.com>]

On 6-10-2016 10:07, Gucea Doru wrote:
> On Wed, Oct 5, 2016 at 11:12 AM, Arend Van Spriel
> <arend.vanspriel@broadcom.com> wrote:
>> On 4-10-2016 13:39, Gucea Doru wrote:
>>> On Sat, Oct 1, 2016 at 2:52 PM, Arend van Spriel
>>>> <arend.vanspriel@broadcom.com> wrote:
>>>>>
>>>>>
>>>>> On 29-09-16 13:32, Gucea Doru wrote:
>>>>>> On Tue, Sep 27, 2016 at 12:03 PM, Gucea Doru <gucea.doru@gmail.com> wrote:
>>>>>>> What is the decision triggering the exit from the PS mode immediately
>>>>>>> after the ping request? I am asking this because 802.11 PS legacy
>>>>>>> specifies that the client should wait for a beacon with TIM set in
>>>>>>> order to wake up: in my case, there is no beacon between the ping
>>>>>>> request message and the Null frame that announces the exit from the PS
>>>>>>> mode.
>>>>>>
>>>>>>
>>>>>> Any help would be highly appreciated :)
>>>>>
>>>>> Actually though I already sent you are reply, but alas here it is.
>>>>>
>>>>> bcmdhd is our aosp driver. I am maintaining the upstream brcm80211
>>>>> drivers. Regardless your question is more for firmware running on the
>>>>> device. So like the same behavior would be observed when using brcmfmac
>>>>> with same firmware.
>>>>>
>>>>>> IEEE Std 802.11-2012, section 10.2.1.8 specifies that "when the STA
>>>>>> detects that the bit corresponding to its AID is 1 i the TIM, the STA
>>>>>> shall issue a PS Poll". In my capture there are cases when the STA
>>>>>> exits the PS mode without waiting for a beacon.
>>>>>
>>>>> It is a bit tricky, but the standard does not explicitly say the STA
>>>>> should be in power-save at any other time. So it is difficult to say
>>>>> what event occurred on the STA side to exit PS mode. Also STA means
>>>>> P2P-Client as you say. That means that you have multiple interfaces:
>>>>> regular STA and P2P-Client. So is the STA connected to some other AP or
>>>>> just not connected. wpa_supplicant will do intermittent scan or initiate
>>>>> scheduled scan by which firmware will scan at a certain interval. That
>>>>> is just some things I can come up with and I am sure there are more.
>>>
>>> I agree that there may be some events belonging to the regular STA
>>> interface that could trigger the Null Frame (which includes the exit
>>> from PS Mode). However, I would expect to see some management frames
>>> in the air before/after the Null Packet (e.g.: a Probe request in case
>>> of a scheduled scan). But in my case the trigger for the Null frame
>>> seems to be the ping request packet, the scenario is the same every
>>> time: ping request -> Block ACK -> Null Frame (Wireshark trace
>>> confirms this behavior).
>>>
>>> I thought that you had a power save optimization algorithm that keeps
>>> the card on a few milliseconds just to see if we can have a fast reply
>>> from the peer. Does this ring a bell? :)
>>
>> It does not. That would be implemented in firmware. As said I am working
>> on brcmfmac/brcmsmac. So bcmdhd and firmware are not my expertise.
>>
> 
> Arend, could you please redirect me to a Broadcom firmware maintainer?

Can you please elaborate on your platform, broadcom chipset, and what
version of bcmdhd you are using.

Regards,
Arend