Re: [PATCH v5 2/2] mac80211: support DTPC IE (from Cisco Client eXtensions)

On Fri, 2014-08-29 at 19:38 +0200, Steinar H. Gunderson wrote:

Linux already supports 802.11h, where the access point can tell the
client to reduce its transmission power. However, 802.11h is only
defined for 5 GHz, where the need for this is much smaller than on
2.4 GHz.

Cisco has their own solution, called DTPC (Dynamic Transmit Power
Control). Cisco APs on a controller sometimes but not always send
802.11h; they always send DTPC, even on 2.4 GHz. This patch adds support
for parsing and honoring the DTPC IE in addition to the 802.11h
element (they do not always contain the same limits, so both must
be honored); the format is not documented, but very simple.

The format is documented for CCX partners, I suppose, but we don't have
access to that :)

I think for some vendors shipping our stack this might become
problematic. I think it would make sense to have a Kconfig option for
this, probably hidden away under "if EXPERT" and defaulting to yes, to
enable this code, it might be something that interferes with more CCX
implementations maybe?

+static bool ieee80211_find_cisco_dtpc(struct ieee80211_sub_if_data
*sdata,

The return value is useless here, so it could be void?

+                       if (pos[0] != 0x00 || pos[1] != 0x40 ||
+                           pos[2] != 0x96 || pos[3] != 0x00) {
+                               break;
+                       }

Please remove those useless braces - maybe run ./scripts/checkpatch.pl?

johannes