Re: [PATCH] mac80211: allow disabling 40MHz on 2.4GHz

[Pavel Roskin <proski@gnu.org>]

On Tue, 2009-12-01 at 11:18 -0800, Luis R. Rodriguez wrote:
> >> That looks like a hack to me.
> >>
> >> Maybe it should be treated like other CRDA flags?  In fact, you can find
> >> this in dbparse.py in the wireless-regdb sources:
> >>
> >>     # hole at bit 9. FIXME: Where is NO-HT40 defined?
> >>     'NO-HT40':          1<<10,
> >>
> >> However, there are no other references to NO-HT40 in the wireless-regdb
> >> or CRDA sources.  I assume it's not implemented.
> >
> > It's not a regulatory requirement, it's a coexistence requirement.
> 
> To extend this text a little more, me and Johannes had reviewed usage
> of a NO-HT40 flag for regulatory purposes a while back. It was used
> mainly on the old Atheros HAL regulatory code and upon a lot of review
> even with our own regulatory folks determined that in fact there was
> no specific rules about disallowing 40 MHz, but that when this was
> disallowed it can be implied by the frequency range not fitting a 40
> MHz channel. This is currently computed dynamically now on cfg80211
> and its results are outputed through the file:
> 
> /sys/kernel/debug/ieee80211/phy0/ht40allow_map

OK, good to know.

Anyway, I think that using module parameters for any configuration
creates a bad precedent.  Disabling HT40 in the 2.4GHz band is a "fine
tuning" compared to other settings.  But there may be many other such
"knobs" (e.g. ACK timeout), and if they all are controlled by mac80211
parameters, it would be a maintenance nightmare.

If module parameters are discourages for the drivers, mac80211 should be
held to the same standard.

-- 
Regards,
Pavel Roskin