Kernel Bug Tracker – Bug 14567
Ath5k: Txpower 0 dBm does not work correctly
Last modified: 2009-11-24 07:45:25 UTC
Created attachment 23711 [details]
left 0dBm set, right 1dBm set
I did some testing with ath5k after the txpower of ath5k has become settable in the 2.6.31 kernel. I tested with a Rohde&Schwarz spectrum analyser, and did a channel power measurement. I used a R52H minipci card with Atheros AR5414 chipset in it, using the ath5k driver. The antenna output is connected with a coax cable to the spectrum analyser input (closed system). I used channel 11 (2462MHz) in Ad-Hoc mode. Txpower is set to 0dBm (1mW).
A multicast with a duty cycle of 80% is used.
I did the following setting:
$ iwconfig wlan1 txpower 0
$ iwlist wlan1 txpower
wlan1 unknown transmit-power information
Current Tx-Power=0 dBm (1 mW)
As on the screenshot (left) is seen, the channel output is not 0dBm, but 13dBm.
The second screenshot (right) shows the same test but with txpower 1dBm, which works correcly
Well, this code certainly looks suspect:
ath5k_hw_txpower(struct ath5k_hw *ah, struct ieee80211_channel *channel,
u8 ee_mode, u8 txpower)
if (txpower == 0)
txpower = AR5K_TUNE_DEFAULT_TXPOWER;
Guess what, it's 12.5 dBm... heh.
#define AR5K_TUNE_DEFAULT_TXPOWER 25
Created attachment 23783 [details]
allow txpower = 0
Thank you for the excellent bug report, please let me know if this patch works.
Also if it succeeds, let me know if I can add your 'Reported-by' and 'Tested-by' to the patch.
Created attachment 23797 [details]
txpower 0dBm works (2,10 and 20dBm also included)
You can add my "Reported-By" and "Tested-By" to the patch.
Do you expect this patch will be included in the next kernel-rc?
It's up to John, but my guess is -rc7 is a little too late for 2.6.32, but I marked it for stable so as soon as it hits Linus' tree it will get picked up there -- so likely 18.104.22.168 or .2.