Re: [PATCH v3 11/13] ath9k_hw: Disable Walsh spatial spreading for 2 chains

From: Adrian Chadd <adrian@freebsd.org>
To: Felix Fietkau <nbd@openwrt.org>
Cc: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>,
	linville@tuxdriver.com, linux-wireless@vger.kernel.org
Subject: Re: [PATCH v3 11/13] ath9k_hw: Disable Walsh spatial spreading for 2 chains
Date: Fri, 5 Aug 2011 19:50:44 +0800	[thread overview]
Message-ID: <CAJ-VmomE7UCaetEGQU8xK1ysUyOzr97Wn7TVXAD3CubZfNg8VA@mail.gmail.com> (raw)
In-Reply-To: <4E3BBC7F.9040902@openwrt.org>

.. question: are the regulatory limits programmed into the cards
taking this spreading into effect?

Adrian

On 5 August 2011 17:48, Felix Fietkau <nbd@openwrt.org> wrote:
> On 2011-08-05 10:36 AM, Rajkumar Manoharan wrote:
>>
>> On Fri, Aug 05, 2011 at 08:24:53AM +0530, Rajkumar Manoharan wrote:
>>>
>>>  On Thu, Aug 04, 2011 at 08:23:28PM +0200, Felix Fietkau wrote:
>>>  >  On 2011-08-04 7:54 PM, Rajkumar Manoharan wrote:
>>>  >  >The Walsh bit is disabled for regulatory consideration.
>>>  >  >
>>>  >  >As per the FCC rulings, only transmissions that are completely
>>>  >  >non-coherent, are allowed to waive the array gain contribution
>>>  >  >to EIRP for multi-transmit configurations. The use of 2-stream
>>>  >  >with 2 transmit and use of 3-steam with 3 transmit qualifies
>>>  >  >for this spatial multiplexing MIMO classification as long as
>>>  >  >the streams are directly mapped to each radio (not Walsh spread
>>>  >  >prior to splitting to multiple radios)
>>>  >  I think ath9k does not waive the array gain contribution. I haven't
>>>  >  checked AR9003, but on AR9002 and older, it explicitly includes the
>>>  >  array gain contribution in the tx power limit calculation. I'm not
>>>  >  sure that unconditionally disabling spatial spreading is the right
>>>  >  way to deal with this.
>>>  >
>>>  We might violate the FCC rule with 2x2 config(3dB higher at 2-stream)
>>>  if this bit is enabled. Based on chainmask we can disable Walsh bit.
>>
>> This change does not affect 3x3, since we don't use 2-chain for 2-stream.
>> And Walsh mode would follow INI setting for 2x2 or 3x3 config.
>
> The thing is, on many channels the the card is allowed to transmit at up to
> 27 dBm, and often the hardware does not even get close to that. Why limit tx
> power by disabling this bit in cases where it's not even close to going over
> the limit.
> How about disabling it only if the combined txpower is within x dBm of the
> regulatory limit, or simply adding the same kind of multi-chain limit
> calculation that is being used on AR9280?
>
> - Felix
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