Re: [PATCH] nl80211: Introduce scan flags to emphasize requested scan behavior

[Dan Williams <dcbw@redhat.com>]

On Wed, 2017-12-13 at 19:52 +0200, Jouni Malinen wrote:
> From: Sunil Dutt <usdutt@qti.qualcomm.com>
> 
> This commit defines new scan flags (LOW_SPAN, LOW_POWER,
> HIGH_LATENCY)
> to emphasize the requested scan behavior for the driver. These flags
> are
> optional and are mutually exclusive. Driver shall resort to default
> behavior if a respective flag is not supported. The implementation of
> the respective functionality can be driver/hardware specific.

Can't we have some kind of capability indication that the driver
supports each of these flags or not?  Otherwise we get into a situation
where you just have to try the flag and hope it works, since it doesn't
look like drivers are required to error out if they don't support the
flag.

Dan

> These flags can be used to control the compromise between how long a
> scan takes, how much power it uses, and high accurate/complete the
> scan
> is in finding the BSSs.
> 
> Signed-off-by: Sunil Dutt <usdutt@qti.qualcomm.com>
> Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
> ---
>  include/uapi/linux/nl80211.h | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/nl80211.h
> b/include/uapi/linux/nl80211.h
> index 6dd6939..68fdb95 100644
> --- a/include/uapi/linux/nl80211.h
> +++ b/include/uapi/linux/nl80211.h
> @@ -5059,6 +5059,11 @@ enum nl80211_timeout_reason {
>   * of NL80211_CMD_TRIGGER_SCAN and NL80211_CMD_START_SCHED_SCAN
>   * requests.
>   *
> + * NL80211_SCAN_FLAG_LOW_SPAN, NL80211_SCAN_FLAG_LOW_POWER, and
> + * NL80211_SCAN_FLAG_HIGH_ACCURACY flags are exclusive of each
> other, i.e., only
> + * one of them can be used in the request. If the driver does not
> support the
> + * requested behavior, default scan behavior will be used instead.
> + *
>   * @NL80211_SCAN_FLAG_LOW_PRIORITY: scan request has low priority
>   * @NL80211_SCAN_FLAG_FLUSH: flush cache before scanning
>   * @NL80211_SCAN_FLAG_AP: force a scan even if the interface is
> configured
> @@ -5086,7 +5091,20 @@ enum nl80211_timeout_reason {
>   *	and suppression (if it has received a broadcast Probe
> Response frame,
>   *	Beacon frame or FILS Discovery frame from an AP that the
> STA considers
>   *	a suitable candidate for (re-)association - suitable in
> terms of
> - *	SSID and/or RSSI
> + *	SSID and/or RSSI.
> + * @NL80211_SCAN_FLAG_LOW_SPAN: Span corresponds to the total time
> taken to
> + *	accomplish the scan. Thus, this flag intends the driver to
> perform the
> + *	scan request with lesser span/duration. It is specific to
> the driver
> + *	implementations on how this is accomplished. Scan accuracy
> may get
> + *	impacted with this flag. This flag cannot be used with
> + * @NL80211_SCAN_FLAG_LOW_POWER: This flag intends the scan attempts
> to consume
> + *	optimal possible power. Drivers can resort to their
> specific means to
> + *	optimize the power. Scan accuracy may get impacted with
> this flag.
> + * @NL80211_SCAN_FLAG_HIGH_ACCURACY: Accuracy here intends to the
> extent of scan
> + *	results obtained. Thus HIGH_ACCURACY scan flag aims to get
> maximum
> + *	possible scan results. This flag hints the driver to use
> the best
> + *	possible scan configuration to improve the accuracy in
> scanning.
> + *	Latency and power use may get impacted with this flag.
>   */
>  enum nl80211_scan_flags {
>  	NL80211_SCAN_FLAG_LOW_PRIORITY				
> = 1<<0,
> @@ -5097,6 +5115,9 @@ enum nl80211_scan_flags {
>  	NL80211_SCAN_FLAG_ACCEPT_BCAST_PROBE_RESP		=
> 1<<5,
>  	NL80211_SCAN_FLAG_OCE_PROBE_REQ_HIGH_TX_RATE		
> = 1<<6,
>  	NL80211_SCAN_FLAG_OCE_PROBE_REQ_DEFERRAL_SUPPRESSION	
> = 1<<7,
> +	NL80211_SCAN_FLAG_LOW_SPAN				=
> 1<<8,
> +	NL80211_SCAN_FLAG_LOW_POWER				=
> 1<<9,
> +	NL80211_SCAN_FLAG_HIGH_ACCURACY				
> = 1<<10,
>  };
>  
>  /**