hostapd and 11h support

Arend van Spriel arend
Wed Dec 24 10:29:04 PST 2014

On 12/24/14 18:32, Jouni Malinen wrote:
> On Wed, Dec 24, 2014 at 10:32:23AM +0100, Arend van Spriel wrote:
>> I am looking at 11h support in hostapd. The supplicant uses
>> .start_dfs_cac() driver callback (resulting in
>> NL08211_CMD_RADAR_DETECT) and basically the CAC logic is done in the
>> supplicant. Now for our devices the entire radar detection and CAC
>> state machine is built in firmware. So hostapd would just need to
>> enable 11h in the driver/firmware.
>> I am considering a new offload feature flag, but not sure whether we
>> would need to introduce a new nl80211 command. I am thinking we
>> could just reuse .start_dfc_cac(). Because of the feature flag it
>> would have a different meaning in the driver. Wanted to know your
>> opinion on this approach before starting the work.
> There's already one vendor-specific mechanism for supporting such
> offloading.. Could you please check whether that would work for your
> driver as well? Search for WPA_DRIVER_FLAGS_DFS_OFFLOAD to see how the
> hostapd-based operations are skipped. This driver flag is currently set
> based on a QCA vendor specific driver capability indication.

Thanks for the info.

> I'm not sure I understood why we would use .start_dfs_cac() for a driver
> that takes care of CAC logic completely (i.e., I'd assume the driver
> would be capable of handling this automatically without additional input
> from user space). I don't really want to get N+1 different ways of doing
> DFS offloading, so if you can either use as-is or build on top of the
> existing design (without breaking it for other, obviously), that would
> be preferred.

The firmware on the device *can* have CAC logic built-in. When it *is* 
built-in it is however disabled by default. Based on your feedback I 
will just detect firmware support, enable dfs in firmware, and signal 
DFS offload to hostapd. I would suggest introducing a new common 
capability flag for this instead of using a QCA vendor specific one. 
That would be odd ;-)


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