Message-ID: <1340868682.4491.1.camel@jlt3.sipsolutions.net> (sfid-20120628_093140_263118_E4020FAD)
Subject: Re: [RFC v3] initial channel context implementation
From: Johannes Berg <johannes@sipsolutions.net>
To: Michal Kazior <michal.kazior@tieto.com>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
Date: Thu, 28 Jun 2012 09:31:22 +0200
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On Thu, 2012-06-28 at 08:04 +0200, Michal Kazior wrote:

> > In any case, I think you're turning it upside down. I think we should
> > get rid of local->oper_channel(_type) completely, and instead use the
> > channel contexts in mac80211 everywhere. If the driver doesn't implement
> > channel contexts it can only support a single channel. Thus, we can have
> > at most one channel context, so whenever a new context is added (there
> > could be zero) or any context is modified (the only one) we can set
> > hw.conf.channel and call hw_config() with the CHANNEL_CHANGE flag.
> >
> > IOW, nothing in mac80211 would ever call hw_config() for the channel or
> > channel type change, it would all do channel contexts, but the channel
> > context code would see that if the driver doesn't support channel
> > contexts
> >   1) there will be at most one context in mac80211
> >   2) this context is programmed into the device by using hw_config()
> >      instead of the context callbacks
> 
> Yes, this is more or less what I also had in mind. I was just thinking 
> about solving the issue of channel context and hw.conf.channel 
> consistency. If we switch a channel we either modify channel in channel 
> context directly (violating the immutability of channel contexts) or we 
> iterate and re-set the new channel on each interface (because 
> single-channel drivers may still have multiple interfaces and we 
> probably want to use sdata->vif.chanctx_conf->channel instead of 
> hw.conf.channel inside mac80211).
> 
> Now that I think about it I guess violating the immutability for the 
> single-channel case is okay. It would greatly simplify the code and we'd 
> just put a comment down in hw_config where the only violation would occur.

I'm not sure why we would violate it? The way I see it, you'd never
change the channel context channel since internally in mac80211 you'd
never want to see a different channel, just like today we use
local->oper_channel everywhere we'd then use sdata->vif.chanctx->channel
throughout, right?

I think the only thing we need to do is put something like this into
hw_config:

 if (local->tmp_channel) {
    local->hw.conf.channel = local->tmp_channel;
    ...
 } else {
    local->hw.conf.channel = chanctx->channel;
 }

No?

johannes