"channel [21] (157) is disabled for use in AP mode"

[Zack Buhman]

On Sun, Apr 28, 2013 at 03:58:43PM +0300, Jouni Malinen wrote:
> The passive scanning part there indicates that no radiation can be
> initiated on the channel (i.e., need to see a master device operating on
> the channel before transmitting any frames).

I find this information extremely useful; thank you.

> It's not hostapd, but the regulatory code or driver that has marked the
> channel as not allowed for AP mode:
> 5785 MHz [157] (17.0 dBm) (passive scanning, no IBSS)

But the regulatory code did no such thing (so far as I can tell); that
iw list output doesn't at all match the iw reg get. Wireless-regdb [2]
doesn't define passive-scanning anywhere in the US regdom, and according
to iw list [1], there's in fact exactly zero 5GHz channels that I can
use in AP mode (all either disabled or passive scanning). Why?

[1] http://ix.io/5o
[2] https://git.kernel.org/cgit/linux/kernel/git/linville/wireless-regdb.git/tree/db.txt#n752