Subject: Re: Wi-Fi Disconnection on Suspend for no wowlan triggers
To: Steve deRosier <derosier@gmail.com>,
        Sunil Dutt Undekari <usdutt@qti.qualcomm.com>
References: <0663e93cc5ca45e6b7191760414b1189@aphydexm01f.ap.qualcomm.com>
 <CALLGbRJgAtOdZ1puzfgpWxc_ZrDVmWXtmFrBu=-gA0C++WrLoA@mail.gmail.com>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
        "johannes@sipsolutions.net" <johannes@sipsolutions.net>,
        Jouni Malinen <jouni@qca.qualcomm.com>,
        Amarnath Hullur Subramanyam <amarnath@qti.qualcomm.com>,
        Rajesh Chauhan <rajeshc@qti.qualcomm.com>
From: Arend van Spriel <arend.vanspriel@broadcom.com>
Message-ID: <5AC5D33F.4090100@broadcom.com> (sfid-20180405_094200_504747_90E0C585)
Date: Thu, 5 Apr 2018 09:41:51 +0200
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On 4/3/2018 6:55 PM, Steve deRosier wrote:
> Hi Sunil,
>
> On Tue, Apr 3, 2018 at 5:39 AM, Sunil Dutt Undekari
> <usdutt@qti.qualcomm.com> wrote:
>> Hi All ,
>>
>> I would like to discuss on the commit 8125696991194aacb1173b6e8196d19098b44e17 (cfg80211/mac80211: disconnect on suspend) which triggers the STA disconnection on suspend if no wowlan triggers are registered.
>
> This commit went in over five years ago. Sometime around v3.9
>
>> I guess the intention here is to disconnect from the AP if the device cannot wake up on a packet / not configured with wowlan triggers .
>
> It being a long time and not feeling like digging too deep into the
> patch, what I can guess from a quick look is basically this:
>
> * Before the patch, waking up from suspend would throw warnings into
> the log. This patch fixes this.
> * As you can't wake the processor, and you're a thin-mac chip who
> depends on mac80211, you _can't_ do anything without wowlan.
> * If your chip is not configured for wowlan, on a suspend, it might as
> well go to sleep, as there's no sense in wasting power as you can't do
> anything anyway.
> * If you're going to sleep and can't respond to the AP, it's polite to
> disconnect. And the AP is going to forcibly do so to you anyway after
> some time of not hearing from you.
>
> Hence the above in general concept seems perfectly correct and I don't
> see any point in doing anything else with a mac80211 device.
>
>> Can this behavior get enhanced to only do so on driver's preference -  do a disconnect for only the host drivers that would want to do so (through an additional feature capability) ?
>>
>
> Can? Perhaps. Send a patch. And maybe you could explain in detail what
> the actual problem is you're trying to solve. Patches that are "maybe,
> someday, someone might want to..." don't have a terribly high chance
> of getting merged.  But solutions to real-life actual problems do. And
> it's really difficult for us to speak on vague hypothetical musings.

So for a full-mac device or a mac80211 device with certain offloads 
(that we may already have, eg. 4way-hs offloads) you could keep up the 
connection for a while, but if it is receiving data it probably wants to 
wake-up the host at some point. So if such a device has means to do a 
host wake-up you could keep the connection upon suspend. You could 
consider such behavior a wowlan trigger as well and extend that.

Regards,
Arend