Re: [PATCH] mac80211: Add module parameter for setting initial rate in rc80211_simple

[James Ketrenos <jketreno@linux.intel.com>]

James Ketrenos wrote:
> Larry Finger wrote:
>> The initial rate for STA's using rc80211_simple is set to the last
>> rate in the rate table. This is too fast for the bcm43xx-mac80211
>> driver.
>> To correct this situation without affecting any other driver,
>> an initial_rate parameter is added to the rc80211_simple module. This
>> parameter is set to 10 times the desired initial rate. If the parameter
>> is zero or not set, the original behavior is kept. If the parameter
>> does not match a valid rate, the first rate in the table will be set.
> 
> Initial rate selection should be based on the RSSI of the last frame(s) 
> received from the target network.  One way to do that would be for the 
> driver to map a minimum RSSI value to each rate.  If the RSSI for the 
> target network is greater than the value listed, that rate could be used 
> for initial selection.  The ieee80211_rate with the highest 'rate', 
> which is in the supported rates mask and with a min_rssi <= the AP's 
> reported RSSI, is selected.
> 
> The mechanism by which the magic values for min_rssi are determined for 
> each rate is more observational than scientific--and is vendor 
> specific.  You can pick a set of values, but different hardware and 
> environments will yield different levels of success / failure.  Some 
> hardware can be very lenient if it has automatic hardware retry.  Other 
> hardware will need to be very conservative (since, as you point out, the 
> first few frames Tx/Rx'd are important)

I didn't state it above -- doing what is described requires adding one unsigned char (min_rssi) to ieee80211_rate in mac80211.h and then modifying rc80211_simple to take advantage of that information (so if you're grepping for min_rssi and can't find it, that's why...)

James

> 
> James
> 
>>
>> Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
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