wifi: ath11k: Optimize 6 GHz scan time

Currently, time taken to scan all supported channels on WCN6750
is ~8 seconds and connection time is almost 10 seconds. WCN6750
supports three Wi-Fi bands (i.e., 2.4/5/6 GHz) and the numbers of
channels for scan come around ~100 channels (default case).
Since the chip doesn't have support for DBS (Dual Band Simultaneous),
scans cannot be parallelized resulting in longer scan times.

Among the 100 odd channels, ~60 channels are in 6 GHz band. Therefore,
optimizing the scan for 6 GHz channels will bring down the overall
scan time.

WCN6750 firmware has support to scan a 6 GHz channel based on co-located
AP information i.e., RNR IE which is found in the legacy 2.4/5 GHz scan
results. When a scan request with all supported channel list is enqueued
to the firmware, then based on WMI_SCAN_CHAN_FLAG_SCAN_ONLY_IF_RNR_FOUND
scan channel flag, firmware will scan only those 6 GHz channels for which
RNR IEs are found in the legacy scan results.

In the proposed design, based on NL80211_SCAN_FLAG_COLOCATED_6GHZ scan
flag, driver will set the WMI_SCAN_CHAN_FLAG_SCAN_ONLY_IF_RNR_FOUND flag
for non-PSC channels. Since there is high probability to find 6 GHz APs
on PSC channels, these channels are always scanned. Only non-PSC channels
are selectively scanned based on cached RNR information from the legacy
scan results.

If NL80211_SCAN_FLAG_COLOCATED_6GHZ is not set in the scan flags,
then scan will happen on all supported channels (default behavior).

With these optimizations, scan time is improved by 1.5-1.8 seconds on
WCN6750. Similar savings have been observed on WCN6855.

Tested-on: WCN6750 hw1.0 AHB WLAN.MSL.1.0.1-00887-QCAMSLSWPLZ-1
Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.16
Signed-off-by: Manikanta Pubbisetty <quic_mpubbise@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230323060913.10097-1-quic_mpubbise@quicinc.com

drivers/net/wireless/ath/ath11k/mac.c

@@ -3819,8 +3819,29 @@ static int ath11k_mac_op_hw_scan(struct ieee80211_hw *hw,
 			goto exit;
 		}
 
-		for (i = 0; i < arg->num_chan; i++)
-			arg->chan_list[i] = req->channels[i]->center_freq;
+		for (i = 0; i < arg->num_chan; i++) {
+			if (test_bit(WMI_TLV_SERVICE_SCAN_CONFIG_PER_CHANNEL,
+				     ar->ab->wmi_ab.svc_map)) {
+				arg->chan_list[i] =
+					u32_encode_bits(req->channels[i]->center_freq,
+							WMI_SCAN_CONFIG_PER_CHANNEL_MASK);
+
+				/* If NL80211_SCAN_FLAG_COLOCATED_6GHZ is set in scan
+				 * flags, then scan all PSC channels in 6 GHz band and
+				 * those non-PSC channels where RNR IE is found during
+				 * the legacy 2.4/5 GHz scan.
+				 * If NL80211_SCAN_FLAG_COLOCATED_6GHZ is not set,
+				 * then all channels in 6 GHz will be scanned.
+				 */
+				if (req->channels[i]->band == NL80211_BAND_6GHZ &&
+				    req->flags & NL80211_SCAN_FLAG_COLOCATED_6GHZ &&
+				    !cfg80211_channel_is_psc(req->channels[i]))
+					arg->chan_list[i] |=
+						WMI_SCAN_CH_FLAG_SCAN_ONLY_IF_RNR_FOUND;
+			} else {
+				arg->chan_list[i] = req->channels[i]->center_freq;
+			}
+		}
 	}
 
 	if (req->flags & NL80211_SCAN_FLAG_RANDOM_ADDR) {

drivers/net/wireless/ath/ath11k/wmi.h

@@ -2100,6 +2100,7 @@ enum wmi_tlv_service {
 
 	/* The second 128 bits */
 	WMI_MAX_EXT_SERVICE = 256,
+	WMI_TLV_SERVICE_SCAN_CONFIG_PER_CHANNEL = 265,
 	WMI_TLV_SERVICE_REG_CC_EXT_EVENT_SUPPORT = 281,
 	WMI_TLV_SERVICE_BIOS_SAR_SUPPORT = 326,
 
@@ -3249,6 +3250,9 @@ struct  wmi_start_scan_cmd {
 #define WMI_SCAN_DWELL_MODE_SHIFT        21
 #define WMI_SCAN_FLAG_EXT_PASSIVE_SCAN_START_TIME_ENHANCE   0x00000800
 
+#define WMI_SCAN_CONFIG_PER_CHANNEL_MASK	GENMASK(19, 0)
+#define WMI_SCAN_CH_FLAG_SCAN_ONLY_IF_RNR_FOUND	BIT(20)
+
 enum {
 	WMI_SCAN_DWELL_MODE_DEFAULT      = 0,
 	WMI_SCAN_DWELL_MODE_CONSERVATIVE = 1,