Re: RFC Patch v2: Add signal strength to nl80211station info

[Henning Rogge <rogge@fgan.de>]

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Am Thursday 04 December 2008 22:20:35 schrieb Johannes Berg:
> On Thu, 2008-12-04 at 13:12 -0800, Luis R. Rodriguez wrote:
> > It seems that's the case for ath9k, at least Jouni had pointed out to me.
>
> They cannot, we don't even have that in the API.
Ath9k has it's ***_ratetable which contains a line of data for each 
transmission range. 20/40Mhz and guard interval is already contained in this 
table (encoded in "phy" variable). Just the MCS number is missing.

And I think the intel driver has the necessary data too. If I understand the 
iwl5000 driver, it pushes the rate index (even for 802.11n) through 
ieee80211_rx_status into mac80211.

> > > then we also don't need the values for the number of streams since
> > > those are perfect multiples (1x, 2x, 3x, 4x for up to 4 streams).
> >
> > Well if you have the MCS index and HT mode you get the # of streams. Not
> > sure I understood the perfect multiple stuff.
>
> Right, but you don't need to store a bitrate for MCS 0, 8, 16 and 24,
> the latter three can just use the first multiplied by 2, 3 and 4
> respectively.
When I looked at the table in the wiki I noticed it cannot be created just by 
a little bit arithmetric ? Maybe someone can look at the 802.11 draft if we 
don't need the tables at all but just use a formula ? If yes we could remove 
them from kernelspace and just add a macro for calculating the rate into a 
userspace-accessable header file.

> > > Just had another idea. Since we'll end up duplicating these for TX and
> > > RX (ultimately we'll need RX_BITRATE_40_MHZ/MCS/SGI etc too) we should
> > > actually do this differently:
> > >
> > >  1) define NL80211_STA_INFO_RATE,
> > >  2) define NL80211_RATE_INFO_BITRATE/40/MCS/SGI
> > >
> > > and then nest the bitrate information into the STA_INFO_RATE, just like
> > > station flags are nested etc. That way the RATE_INFO things could also
> > > be used elsewhere.
> >
> > So we'll have to add an enum then too to distinguish which rate this is
> > for.
>
> No, we know that based on what "container" attribute it's contained in,
> in netlink.
So it's possible to define a substructure in the station info in nl80211 ? 
Sounds like a nice way to construct the tx/rx rate.

I will see if I get a "v6" patch ready during the weekend.

Henning

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