Re: ath9k max_power question

[Felix Fietkau <nbd@openwrt.org>]

On 2010-11-11 8:22 PM, Luis R. Rodriguez wrote:
> On Thu, Nov 11, 2010 at 11:15 AM, Mark Mentovai <mark@moxienet.com> wrote:
>> In drivers/net/wireless/ath/ath9k/init.c, both CHAN2G and CHAN5G set
>> .max_power to 20, represented in dBm. I’m wondering how this number
>> was chosen. Is it simply a safe generic value? I’m dealing with a
>> device on which the vendor’s madwifi-based binary driver would show
>> 23dBm for 2.4GHz and 18dBm for 5GHz (although only when I asked it for
>> 26dBm and 24dBm respectively, so I’m not sure which set of numbers to
>> believe.)
>>
>> I noticed that in ath9k, if these .max_power limits are raised, the
>> driver is happy to set a somewhat higher transmit power. In this case,
>> it will max out at 25dBm for 2.4GHz and 21dBm for 5GHz. These are
>> still below the relevant regulatory limits. These values seem to be
>> computed by routines in eeprom_*.c, so I’m wondering if they’re based
>> on the card’s own data and safe to use without fear of burning the
>> radios.
> 
> The values are just some safe value to use as defaults but will
> quickly be replaced by the max regulatory allowed and then upon
> further inspection also capped to the lower value of the regulatory
> limit, the max allowed device limit (where things start becoming
> unreliable), and the CTL indexed limit which is calibrated
> specifically for the card you use, so this will vary. You can read
> more about it here:
> 
> http://wireless.kernel.org/en/users/Drivers/ath
That should have already been taken care of by this commit (w-t):

commit 6cdd07721180145b7ef46bd63f1eee636983f0e6
Author: Felix Fietkau <nbd@openwrt.org>
Date:   Wed Oct 20 02:09:46 2010 +0200

ath9k: initialize per-channel tx power limits instead of hardcoding them


- Felix