Re: [PATCH 1/3] ath9k: use consistent value for REDUCE_SCALED_POWER_BY_THREE_CHAIN

[Gabor Juhos <juhosg@openwrt.org>]

Hi Dan,

Thank you for the comments.

> (Failed to reply-all originally, sorry:)
> 
> Erm...
> 
> On Sat, Apr 14, 2012 at 1:01 PM, Gabor Juhos <juhosg@openwrt.org> wrote:
>>
>> In eeprom_def.c and in ar9003_eeprom.c the value
>> of the symbol is 9, however the comments in these
>> files indicates the value should be 10*log10(3)*2
>> which is 9.54242509439325. Replace the the value
>> to 10 in these files.
> 
> So the truncated constant is off by a quarter-dB for 9 or for 10. Do
> the chips care one way or the other? (For comparison, Intel uses 4.5
> dB, i.e. 9 in this notation, to mean "divide-by-3". That's what ath9k
> has now).

In my understanding the value is not related to the chip. It is used for
per-chain tx power reduction, in order to ensure regulatory compliance. Using 10
instead of 9 means that the overall tx power will be lower.

> Are you making it consistent with some other file that's not mentioned
> here? If not, why?

I'm tyring to make it consistent between ar9003_eeprom.c, eeprom_def.c and
eeprom_9287.c. The first two files uses 9, whereas eeprom_9287 uses 10.

Considering Felix's comment, I will update the patch and will use 9 instead of
10. Although that will replace the value in eeprom_9287.c, but that should not
cause problems, because the AR9287 does not supports 3x3.

>>  #define REDUCE_SCALED_POWER_BY_TWO_CHAIN     6  /* 10*log10(2)*2 */
>> -#define REDUCE_SCALED_POWER_BY_THREE_CHAIN   9  /* 10*log10(3)*2 */
>> +#define REDUCE_SCALED_POWER_BY_THREE_CHAIN   10 /* 10*log10(3)*2 */
>>  #define PWRINCR_3_TO_1_CHAIN      9             /* 10*log(3)*2 */
> 
> Why only change one of two 9s to a 10? Why not also PWRINCR_3_TO_1_CHAIN?

The PWRINCR_* symbols are not used anywhere and should be removed.

-Gabor