Return-path: Received: from nbd.name ([46.4.11.11]:56802 "EHLO nbd.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753453Ab3FGRdV (ORCPT ); Fri, 7 Jun 2013 13:33:21 -0400 Message-ID: <51B2195C.1010303@openwrt.org> (sfid-20130607_193324_083096_0546FCDE) Date: Fri, 07 Jun 2013 19:33:16 +0200 From: Felix Fietkau MIME-Version: 1.0 To: Simon Wunderlich CC: linux-wireless@vger.kernel.org, Johannes Berg , Mathias Kretschmer , Simon Wunderlich Subject: Re: [PATCH 0/5] add master channel switch announcement support References: <1370624745-2267-1-git-send-email-siwu@hrz.tu-chemnitz.de> In-Reply-To: <1370624745-2267-1-git-send-email-siwu@hrz.tu-chemnitz.de> Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 2013-06-07 7:05 PM, Simon Wunderlich wrote: > This is the follow up from the RFC posted a month ago. This patchset adds generic > channel switch support for AP. This is required for DFS operation > (e.g. Wi-Fi Alliance requires this for 802.11h certification). This will also > be required for IBSS-DFS later. > > The rough design is: > * userspace asks kernel to switch a channel using the new NL80211_CMD_CHANNEL_SWITCH > command. It supplies IE information for the time while staying on the old channel and > announcing the switch, and IE information for after the switch to the new channel. > * IE information contains the beacon and optionally probe responses, which should > include (E)CSA IEs for the CSA case. Furthermore an offset is provided (for beacon > and probe response) to point to the counter field within the channel switch IEs. > * The driver gets the new beacons passed and must set them, and decrement the > counter field. When it reaches 0, the channel is changed and userspace notified. > > Discussion points: > * Assembling all these IE information is a little bit tedious but doable (I've > patched hostapd). > * Other future users like IBSS/MESH will not get the beacon/probe response IEs, as they > generate these beacons themselves. Therefore they need the COUNT attribute, which > is kind of duplicate right now. > * Userspace must generate/handle all IEs, which lifts the previous limitations of > the RFC (e.g. no change of band allowed, no operation mode change allowed). > * it currently works for me [TM] on my ath9k based machine I think this is a bit racy. Just because the driver gets a beacon from mac80211 doesn't mean that the beacon will be sent *immediately*. I'd recommend calling back from the driver into mac80211 on beacon tx completion. Also, it might make sense to skip CAB queue transmissions in this case. - Felix