Re: [PATCH v2 0/7] mt76x02: Beacon support for USB

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Tue, Jan 29, 2019 at 01:10:08PM +0100, Felix Fietkau wrote:
> 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.

But how serious problem of dropping multicast frames for PS stations is?
I don't think from user perspective this is "sometimes my connection
work and sometimes not", but something much less annoying. 

Another thing is that this (D)TIM PS is not reliable by design,
that why UAPSD was introduced.

Moreover in the tree we have already bunch of drivers that do 
advertise AP mode support without HOST_BROADCAST_PS_BUFFERING 
like iwlwifi or brcm80211 .

So I don't think we should drop AP flag, AP mode works with
this patch set quite well.

Thanks
Stanislaw