Date:   Wed, 30 Jan 2019 09:37:47 +0100
From:   Stanislaw Gruszka <sgruszka@redhat.com>
To:     Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Cc:     Kalle Valo <kvalo@codeaurora.org>, Felix Fietkau <nbd@nbd.name>,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH v2 0/7] mt76x02: Beacon support for USB
Message-ID: <20190130083747.GB2720@redhat.com>
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On Tue, Jan 29, 2019 at 01:40:57PM +0100, Lorenzo Bianconi wrote:
> > Felix Fietkau <nbd@nbd.name> writes:
> > 
> > > On 2019-01-29 13:07, Kalle Valo wrote:
> > >> Felix Fietkau <nbd@nbd.name> writes:
> > >> 
> > >>> On 2019-01-29 12:47, Kalle Valo wrote:
> > >>>> Stanislaw Gruszka <sgruszka@redhat.com> writes:
> > >>>> 
> > >>>>> We can configure beaconing, but without TBTT interrupt we
> > >>>>> can not support PS buffering. This can be added later using
> > >>>>> kernel hrtimer, if we can keep it in sycn with device timer.
> > >>>>>
> > >>>>> I tested AP and IBSS modes.
> > >>>> 
> > >>>> So how does this work reliably so that there's no packet loss with
> > >>>> clients using power save?
> > >>>
> > >>> There will be multicast packet loss for clients using power save.
> > >> 
> > >> Isn't that a problem? At least as a normal user I would very frustrated
> > >> if sometimes my connection work and sometimes not, for example if I'm
> > >> trying discover devices from my network. Hopefully nobody won't use USB
> > >> devices for any real AP stuff, but still enabling something which we
> > >> know doesn't work realiably is concerning.
> > >
> > > I agree. Maybe we should leave out the flag for AP mode in this patch
> > > until we have PS buffering and leave the rest of the code intact.
> > 
> > At least for me that sounds good.
> 
> We can support ps buffering in AP as well using a hrtimer. In this way we
> can reuse most of the existing code

Yes, but there is issue to address, since kernel timer and device TBT
timer are independed, they possibly can get out of sync after some time,
for example few hours or days. So there is need to prevent/fix this
somehow.

Thanks
Stanislaw