Re: rt2800, minstrel_ht & mac80211

[Helmut Schaa <helmut.schaa@googlemail.com>]

Am Freitag 04 Juni 2010 schrieb Johannes Berg:
> On Fri, 2010-06-04 at 12:22 +0200, Helmut Schaa wrote:
> 
> > This meant that minstrel most of the time selected MCS15 as tx rate which
> > resulted in a huge number of retries and thus a very slow throughput.
> > 
> > status.c:
> > 
> > 178                 /* the HW cannot have attempted that rate */
> > 179                 if (i >= hw->max_rates) {
> > 180                         info->status.rates[i].idx = -1;
> > 181                         info->status.rates[i].count = 0;
> > 
> > Johannes, is there a valid reason for this check in status.c. Can we remove
> > it without breaking anything else?
> 
> IIRC there were/are some drivers that were not terminating the rates[]
> array correctly with a -1, thus this code.

Understood, so it's a driver workaround ;)

Maybe we should check which driver doesn't set it and fix these?

> > What other options would we have to fix this issue? Just use max_rates = 4 
> > in rt2800 even if we will only use the first rate provided by minstrel and
> > then fall back to the global fallback setup (I tried that already and it
> > works just fine but seems not correct to me)?
> 
> p54 kinda does some trickery in this area too, not really sure what to
> do though.

Thanks for the pointer, p54 just sets max_rates=4 even if it cannot support
it.

So, if you would like to keep the check I'll just use max_rates=4 in rt2800.

Helmut