Re: carl9170: How to control transmit power?

[Christian Lamparter <chunkeey@googlemail.com>]

On Thursday, January 12, 2012 12:07:54 AM Harshal Chhaya wrote:
> Does the carl9170 driver/firmware allow real-time updates to the tx
> power parameter?

No. not yet. 
 
> On my AR9170-based AP, I can't set the tx power using either 'iw' or 'iwconfig'.
> 
> 'iw' fails with an error message:
> 
> root@OpenWrt:/etc/hostapd# iw wlan0 set txpower fixed 10
> command failed: Operation not supported (-95)

iw uses mBm (millibels referenced to 1 milliwatt) rather than the more familiar dBm.
try: iw wlan0 set txpower fixed 1000
 
> 'iwconfig' seems to update the information that's displayed but it
> doesn't affect the actual tx power
> 
> root@OpenWrt:/# iwconfig wlan0
> wlan0     IEEE 802.11bgn  Mode:Master  Frequency:2.412 GHz  Tx-Power=7 dBm
>           RTS thr:off   Fragment thr:off
>           Power Management:off
> 
> root@OpenWrt:/# iwconfig wlan0 txpower 11
> 
> root@OpenWrt:/# iwconfig wlan0
> wlan0     IEEE 802.11bgn  Mode:Master  Frequency:2.412 GHz  Tx-Power=11 dBm
>           RTS thr:off   Fragment thr:off
>           Power Management:off
> 
> Is there another way to set the tx power? I want to reduce the range
> of my AP and am trying to lower the tx power.

see attached patch. But I have to add that it won't change the
txpower of frames which are generated by the MAC [like RTS/CTS and
(B)ACKS].

Best Regards and good night.
---
diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index d19a9ee..771e1a9 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -719,6 +719,8 @@ static void carl9170_tx_rate_tpc_chains(struct ar9170 *ar,
 		else
 			*chains = AR9170_TX_PHY_TXCHAIN_2;
 	}
+
+	*tpc = min_t(unsigned int, *tpc, ar->hw->conf.power_level * 2);
 }
 
 static __le32 carl9170_tx_physet(struct ar9170 *ar,