There's already code in the driver that subtracts 3 and 5 dB from the max TX power. Some NICs have value=0 for pwrdecrease2chain and pwrdecrease3chain; I have a feeling the EEPROMs in those have been programmed assuming 2 or 3 chain TX with the current setting (ie, AR_PHY_FC_WALSH in AR_PHY_TURBO). If they've calibrated the EEPROM settings based on that bit being set for 2 or 3 chain TX, you may find they're already doing the "right" thing. Flipping that bit off (and unconditionally subtracting TX power) may result in a lower TX power than regulatory? I do suggest that someone with the relevant test equipment do some investigation into what the behaviour is of a variety of NICs. I'd love to survey what's going on but I'd have to acquire access to a spectrum analyser. Adrian On 5 August 2011 10:54, Rajkumar Manoharan <rmanohar@xxxxxxxxxxxxxxxx> 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. > Any comments? > > -- > Rajkumar > -- > To unsubscribe from this list: send the line "unsubscribe linux-wireless" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
