Re: [PATCH 4/4] nl80211: add VHT support for set_bitrate_mask

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2013-12-03 at 17:21 +0100, Janusz Dziedzic wrote:

> We need this for test purpose. Need to test different MCS/NSS
> configurations using our HW (mainly for VHT).
> Our HW supports setting TX fixed_rate for legacy/HT/VHT.
> So, we decided to use set_tx_bitrate_mask() as the best interface for
> that in nl80211.
> And after that we realize VHT implementation/change will be needed in
> nl80211/iw also.
> Because of that I send this VHT patch.
> So, we need this :)

Fair enough - please add a line or two to the commit log.

> >> +#define NL80211_MAX_SUPP_VHT_RATES           80
> >
> > Where does 80 come from? That seems odd?
> >
> NSS_MAX (8) * MCS_MAX (10)
> 
> Eg.
> 9 - NSS=1, MCS=9
> 10 - NSS=2, MCS=0
> 11 - NSS=2, MCS=1
> ...

Can we please find a better way to encode this?

> >> + * @NL80211_TXRATE_VHT_MCS: VHT (MCS) rates allowed for TX rate selection
> >> + *   in an array of MCS numbers.
> >
> > VHT has no "MCS numbers", so this doesn't make much sense?
> >
> You mean description only or mcs mask for vht (like above)?

Well, for VHT, there's no single "MCS" identifier for a rate, rates are
identified using MCS (0-9) and NSS (1-8). In mac80211, we do some bit
tricks to fit them into a single byte, but I see no reason to do this in
the nl80211 API and would rather have an API that makes this obvious.
The easiest would be using a struct, but then you don't need 80 bytes,
only 8 bitmaps (one for each NSS), for example.

johannes