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Re: bcmdhd: Strange Power Save messages

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On Wed, Oct 5, 2016 at 11:12 AM, Arend Van Spriel
<arend.vanspriel@xxxxxxxxxxxx> wrote:
> On 4-10-2016 13:39, Gucea Doru wrote:
>> On Sat, Oct 1, 2016 at 2:52 PM, Arend van Spriel
>>> <arend.vanspriel@xxxxxxxxxxxx> wrote:
>>>>
>>>>
>>>> On 29-09-16 13:32, Gucea Doru wrote:
>>>>> On Tue, Sep 27, 2016 at 12:03 PM, Gucea Doru <gucea.doru@xxxxxxxxx> 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?

Thank you,
Doru



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