Re: [PATCH v2 4/4] ath9k_hw: Fix tx power settings for AR9003

[Felix Fietkau <nbd@openwrt.org>]

On 2011-11-10 10:44 AM, Rajkumar Manoharan wrote:
> Retriving tx power for 2x2 and 3x3 chainmask is not handled
> properly. While calculating tx power for 2x2, 3 dBm was reduced
> and for 3x3, 5 dBm was reduced which should be added back when
> retriving.
>
> Cc: Paul Stewart<pstew@google.com>
> Signed-off-by: Rajkumar Manoharan<rmanohar@qca.qualcomm.com>
I think the tx power reduction for 2x2/3x3 needs to be revisited. In the 
discussion that led to Walsh spatial spreading being disabled you 
mentioned this:

> In 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)
So if I understand this issue correctly, Walsh spatial spreading was 
disabled so that the tx power for 2x2 or 3x3 would not have to be 
reduced by the array gain contribution - yet we're still doing that.

When Adrian pointed out that tx power is reduced based on the number of 
chains, you mentioned this:
> Those pwrdecrease fields are applicable for AR9280 chips not for AR9003.

According to this patch, this doesn't seem to match what the code does, 
though I didn't notice it back then.

So before we merge this patch, let's decide whether we actually need 
this tx power reduction or not.

- Felix