Re: bcmdhd: Strange Power Save messages

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

On 12-10-16 16:26, Gucea Doru wrote:
> On Tue, Oct 11, 2016 at 10:12 PM, Arend van Spriel
> <arend.vanspriel@broadcom.com> wrote:
>> On 07-10-16 16:33, Gucea Doru wrote:
>>> On Thu, Oct 6, 2016 at 10:25 AM, Arend Van Spriel
>>> <arend.vanspriel@broadcom.com> wrote:
>>>> 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.
>>>>
>>>
>>> Platform: Nexus 5 running CM13 (Android 6.0.1)
>>> Broadcom chipset: BCM4339 Wi-Fi Chipset
>>> bcmdhd version:Dongle Host Driver, version 1.88.45 (r)
>>>
>>> Do you need more information?
>>
>> So can you indicate the mac addresses of the two nexus devices and which
>> one is P2P-GO. I entered the wpa key you mentioned in your initial
>> email, but my wireshark does not seem to be able to decrypt the packets,
>> which makes it a bit harder to analyze.
> 
> Do you have a wpa-pwd entry "JYdrhZp3:DIRECT-35-Android_Intel" inside
> Edit->Preferences->Protocols->IEEE 802.11->Decryption Keys? I use
> Wireshark 2.0.4.

I see. I only entered the password but not the SSID. The examples showed
SSID was optional. Changed it, but still no luck using 2.2.0.

> P2P-GO MAC: 66:89:9a:81:0d:95
> P2P Client MAC: 66:89:9a:81:0f:20

Actually this was redundant question as it is clear which one sends the
beacon frames. Thanks anyway :-)

Regards,
Arend

> Thanks,
> Doru
>