Re: [PATCH v6 2/2] mac80211: support DTPC IE (from Cisco Client eXtensions)

["Steinar H. Gunderson" <sgunderson@bigfoot.com>]

On Mon, Sep 08, 2014 at 10:53:20AM +0200, Johannes Berg wrote:
>> Linux already supports 802.11h, where the access point can tell the
>> client to reduce its transmission power. However, 802.11h is only
>> defined for 5 GHz, where the need for this is much smaller than on
>> 2.4 GHz.
>> 
>> Cisco has their own solution, called DTPC (Dynamic Transmit Power
>> Control). Cisco APs on a controller sometimes but not always send
>> 802.11h; they always send DTPC, even on 2.4 GHz. This patch adds support
>> for parsing and honoring the DTPC IE in addition to the 802.11h
>> element (they do not always contain the same limits, so both must
>> be honored); the format is not documented, but very simple.
>> 
>> Tested (on top of wireless.git and on 3.16.1) against a Cisco Aironet
>> 1142 joined to a Cisco 2504 WLC, by setting various transmit power
>> levels for the given access points and observing the results.
>> The Wireshark 802.11 dissector agrees with the interpretation of the
>> element, except for negative numbers, which seem to never happen
>> anyway.
> Applied both.

I found what I believe is an edge case: What happens if the element suddenly
goes away from one beacon to another? Shouldn't there be a reset of the power
level and then a new call to __ieee80211_recalc_txpower()?

(If so, I believe this bug was already present in the code before my first
patch, as I understand the existing logic.)

/* Steinar */
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