Message-ID: <4F8B03A3.6030804@openwrt.org> (sfid-20120415_192214_760913_9D38ED18)
Date: Sun, 15 Apr 2012 19:21:39 +0200
From: Gabor Juhos <juhosg@openwrt.org>
MIME-Version: 1.0
To: Felix Fietkau <nbd@openwrt.org>
CC: "John W. Linville" <linville@tuxdriver.com>,
	linux-wireless@vger.kernel.org,
	"ath9k-devel@lists.ath9k.org" <ath9k-devel@venema.h4ckr.net>
Subject: Re: [PATCH 1/3] ath9k: use consistent value for REDUCE_SCALED_POWER_BY_THREE_CHAIN
References: <1334433719-1144-1-git-send-email-juhosg@openwrt.org> <4F8AA38E.1040702@openwrt.org>
In-Reply-To: <4F8AA38E.1040702@openwrt.org>
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Sender: linux-wireless-owner@vger.kernel.org

Hi Felix,

Thank you for the comments.

> On 2012-04-14 10:01 PM, Gabor Juhos wrote:
>> The REDUCE_SCALED_POWER_BY_THREE_CHAIN symbol is
>> defined in different eeprom files, and the value
>> varies between the different files.
>>
>> 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.
>>
>> Also add comments to eeprom_9287.c.
>>
>> Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
> I think we should keep the value 9.
> If I understand the logic behind the power increase through chain
> combining properly, this value only describes the worst-case (wrt.
> regulatory compliance) upper limit of tx power, whereas in practice the
> measured combined power output will be much lower than that due to
> signal/phase differences.
> Regulatory compliance is already properly tested on all devices with the
> truncated value 9, so I don't think that we need to be even more
> conservative and round up here.

Ok, I will rework the patch.

Apart from the inconsistency between the REDUCE_SCALED_POWER_BY_THREE_CHAIN
values, there is another thing which confuses me.

In the 'ath9k_hw_set_*_power_cal_table' functions the driver uses the
REDUCE_SCALED_POWER_BY_THREE_CHAIN constant to reduce the power values.
In the 'ath9k_hw_update_regulatory_maxpower' function it uses the
INCREASE_MAXPOW_BY_THREE_CHAIN constant to compensate the reduction. However the
two constants are different. I might be wrong, but in my opinion the driver
should use the same constant in both functions.

-Gabor