Hi Johannes, This change is originated from a problem caused by OBSS scan and ACS feature in the driver. When SAP is started, hostapd will do an OBSS scan based on the channel setting in hostapd.conf, if the wlan driver has the ACS capability, it may choose a different channel. Even it notifies hostapd about the channel selection, the OBSS scan result may become invalid if a different channel is selected and SAP may end up operating in not desired mode. This change will allow the wlan driver do the ACS and decide a channel, once hostapd is notified, it can then do OBSS scan using that channel. ACS operation is done during SAP starting up, beacon is sent after channel is selected by driver. Thanks, Peng -----Original Message----- From: Johannes Berg [mailto:johannes@xxxxxxxxxxxxxxxx] Sent: Thursday, October 09, 2014 2:46 AM To: Park, Kyeyoon Cc: Xu, Peng; cfg80211mac80211; linux-wireless@xxxxxxxxxxxxxxx Subject: Re: [PATCH] cfg80211: Add support for ACS offloading On Fri, 2014-10-03 at 14:58 -0700, Kyeyoon Park wrote: > From: Peng Xu <pxu@xxxxxxxxxxxxxxxx> > > Add support for offloading ACS functionality to the driver. A new > feature flag NL80211_FEATURE_AP_ACS_OFFLOAD was added to support ACS > (Automatic Channel Selection) offload functionality. This flag allows > the driver to advertise its ACS capability. > > When hostapd starts with the "channel" configuration set to 0, it will > check whether the driver has the capability of doing the ACS on its own. > If the driver has such capability, then the channel selection will be > done in the driver. The kernel will skip the channel information > validation since it would initially be NULL when this feature is > enabled. After the channel is selected by the driver, a channel change > event will be sent from the driver to the kernel which updates the > channel information it maintains. This event is in turn sent to > hostapd and the channel information in hostapd will get updated as well. Is this design required? That seems a bit strange because you'd start the AP with ... invalid beacon information? Invalid probe response, and all that? Even an invalid channel reported to other userspace. I'd much prefer offloading this as a separate operation, with the device reporting back the best channel (configuration) to use, and hostapd then using that to start up its operation. johannes ��.n��������+%������w��{.n�����{���zW����ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f
