[Bugme-new] [Bug 14642] New: ath9k txpower configuration only takes effect after scan

[bugzilla-daemon at bugzilla.kernel.org]

http://bugzilla.kernel.org/show_bug.cgi?id=14642

           Summary: ath9k txpower configuration only takes effect after
                    scan
           Product: Drivers
           Version: 2.5
    Kernel Version: 2.6.32-rc7-wl
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: low
          Priority: P1
         Component: network-wireless
        AssignedTo: drivers_network-wireless at kernel-bugs.osdl.org
        ReportedBy: javier at cozybit.com
        Regression: No


Changing the transmission power while the interface is up and associated has no
effect.  The following sequence of commands will not affect the output power
(verified with a sniffer):

# iwconfig wlan0 txpower 20dbm
# iwconfig wlan0
wlan0     IEEE 802.11abgn  ESSID:"cozyguest"
         Mode:Managed  Frequency:2.462 GHz  Access Point: 00:13:10:XX:XX:XX
         Bit Rate=54 Mb/s   Tx-Power=20 dBm
         ...

# iwconfig wlan0 txpower 0dbm
# iwconfig wlan0
wlan0     IEEE 802.11abgn  ESSID:"cozyguest"
         Mode:Managed  Frequency:2.462 GHz  Access Point: 00:13:10:XX:XX:XX
         Bit Rate=54 Mb/s   Tx-Power=0 dBm
         ...

The changes will take effect if the interface is brought down and up or if a
scan is issued.  

Some notes that may be useful to fix this:

After mac80211 sets IEEE80211_CONF_CHANGE_POWER the driver updates
sc->config.txpowlimit.  The new value is sent to the card by
ath_update_txpow() which is only called by:

  1    364  drivers/net/wireless/ath/ath9k/main.c <<ath_set_channel>>
            ath_update_txpow(sc);
  2   1230  drivers/net/wireless/ath/ath9k/main.c <<ath_radio_enable>>
            ath_update_txpow(sc);
  3   2021  drivers/net/wireless/ath/ath9k/main.c <<ath_reset>>
            ath_update_txpow(sc);
  4   2330  drivers/net/wireless/ath/ath9k/main.c <<ath9k_start>>
            ath_update_txpow(sc);

The new power settings only take effect if one triggers one of these
functions, for instance by issuing a scan.

Don't have a fix at this time.  The obvious fix did not solve the problem:

diff --git a/drivers/net/wireless/ath/ath9k/main.c
b/drivers/net/wireless/ath/ath9k/main.c
index 16bdb1b..b62012e 100644
--- a/drivers/net/wireless/ath/ath9k/main.c
+++ b/drivers/net/wireless/ath/ath9k/main.c
@@ -2795,8 +2795,10 @@ static int ath9k_config(struct ieee80211_hw
*hw, u32 changed)
       }

 skip_chan_change:
-       if (changed & IEEE80211_CONF_CHANGE_POWER)
+       if (changed & IEEE80211_CONF_CHANGE_POWER) {
               sc->config.txpowlimit = 2 * conf->power_level;
+               ath_update_txpow(sc);
+       }

       spin_lock_bh(&sc->wiphy_lock);
       disable_radio = ath9k_all_wiphys_idle(sc);

But issuing a scan after changing the power did:

# iwconfig wlan0 txpower 10dbm; iw dev wlan0 scan

( Scanning seems to be the magic word that one must invoke to get
things done on ath9k: See also bug 14187 )

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