Re: [PATCH 3/3] rt2x00: rt2800: use correct txop value in tx descriptor

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

Am Donnerstag 06 Mai 2010 schrieb Helmut Schaa:
> Am Donnerstag 06 Mai 2010 schrieb Gertjan van Wingerde:
> > On 05/06/10 12:29, Helmut Schaa wrote:
> 
> [...]
> 
> > > diff --git a/drivers/net/wireless/rt2x00/rt2x00ht.c b/drivers/net/wireless/rt2x00/rt2x00ht.c
> > > index 1056c92..5483fec 100644
> > > --- a/drivers/net/wireless/rt2x00/rt2x00ht.c
> > > +++ b/drivers/net/wireless/rt2x00/rt2x00ht.c
> > > @@ -66,4 +66,6 @@ void rt2x00ht_create_tx_descriptor(struct queue_entry *entry,
> > >  		__set_bit(ENTRY_TXD_HT_BW_40, &txdesc->flags);
> > >  	if (txrate->flags & IEEE80211_TX_RC_SHORT_GI)
> > >  		__set_bit(ENTRY_TXD_HT_SHORT_GI, &txdesc->flags);
> > > +
> > > +	txdesc->txop = TXOP_HTTXOP;
> > >  }
> > 
> > I am not too sure about this part. If I look at the Ralink vendor driver, they are most of the time
> > using IFS_BACKOFF (value 3). Why did you put this on TXOP_HTTXOP?
> 
> From what I saw in the ralink driver IFS_BACKOFF is only used for management frames, IFS_SIFS only
> for subsequent frames in a fragment burst and IFS_HTTXOPS for "normal" data frames. But that's
> just the result of a _quick_ review. So I might be wrong here as well :)
> 
> To be honest I don't really know what the device does in case IFS_HTTXOPS is set but that was
> the value we've passed to the driver before ;) (==IFS_BACKOFF on all other ralink chips) and it 
> works quite well. I also tried IFS_BACKOFF and I wasn't able to see a difference when using
> legacy (11b & 11g) rates (neither on the device itself nor with a second machine monitoring
> the traffic).

Ok, after further examination it turns out to be:

- Management frames are sent with IFS_BACKOFF
- Special case for PsPoll frames also with IFS_BACKOFF
- Data frames are sent with IFS_HTTXOP
- Data frame subsequent fragments are send with IFS_SIFS
- CTS frames (in AP mode) use IFS_SIFS

So, I guess I resend this patch after some testing with IFS_BACKOFF for
management frames and IFS_HTTXOP for data frames and SIFS for subsequent
fragments.

John, please don't merge this patch yet. Thanks.

Helmut