On Tue, 2020-03-17 at 18:54 +0200, Kalle Valo wrote:

For me either solutions are good enough, I'm not familiar enough with
all the different SAR user space interfaces to make a good decision.

Brian probably has most insight into this :-)

I really didn't want to have to be the referee here, I was hoping you'd
figure this all out between yourselves... oh well.

But as somebody has said on one of these threads, there seem to
basically be two kinds of APIs:

 1) some kind of platform-dependent index into a table that the
    driver/device has, or perhaps the BIOS; and

 2) some kind of per-band (FSVO band) power restriction like here.


The first is like iwlwifi, and I think Marvell was mentioned? But
they're basically out - there's no information, and there's no clue as
to which indices might even be valid, I think, nor what they mean. So
there isn't really much value in a common API for that since you can't
use it in a common fashion - arguably a common API would be worse...


However, the case of 2, arguably the proposals are very similar?

Qualcomm: optional nl80211_band, 1/2 dBm units
Realtek: 2.4, four 5 GHz subbands, 1/4 dBm units

Both have some strange namespace thing where the same namespace contains
both the outer and inner attributes. Probably should think about the
policy with NLA_POLICY_NESTED and see how that works.


But it any case, these two don't seem like an insurmountable issue to
combine? Say, something like defining a list of affected frequency
ranges in the wiphy properties, and then giving a list of TX powers that
matches the list of frequency ranges? We can go to 1/4 dBm or so, that's
not such a big deal, I'd think?


On the other hand, what does that actually buy us? If you cannot have
common userspace that knows how a given platform must behave, then it's
not very worthwhile to have common API for it?

Brian, what do you think from a platform/userspace perspective - how do
you actually determine the SAR limits? I'm guessing you just have a
table of sorts, but how do you get the table? Would you actually have
common userspace and benefit from having common API?

johannes