wcn36xx: ensure pairing of init_scan/finish_scan and start_scan/end_scan

An SMD capture from the downstream prima driver on WCN3680B shows the
following command sequence for connected scans:

- init_scan_req
    - start_scan_req, channel 1
    - end_scan_req, channel 1
    - start_scan_req, channel 2
    - ...
    - end_scan_req, channel 3
- finish_scan_req
- init_scan_req
    - start_scan_req, channel 4
    - ...
    - end_scan_req, channel 6
- finish_scan_req
- ...
    - end_scan_req, channel 165
- finish_scan_req

Upstream currently never calls wcn36xx_smd_end_scan, and in some cases[1]
still sends finish_scan_req twice in a row or before init_scan_req. A
typical connected scan looks like this:

- init_scan_req
    - start_scan_req, channel 1
- finish_scan_req
- init_scan_req
    - start_scan_req, channel 2
- ...
    - start_scan_req, channel 165
- finish_scan_req
- finish_scan_req

This patch cleans up scanning so that init/finish and start/end are always
paired together and correctly nested.

- init_scan_req
    - start_scan_req, channel 1
    - end_scan_req, channel 1
- finish_scan_req
- init_scan_req
    - start_scan_req, channel 2
    - end_scan_req, channel 2
- ...
    - start_scan_req, channel 165
    - end_scan_req, channel 165
- finish_scan_req

Note that upstream will not do batching of 3 active-probe scans before
returning to the operating channel, and this patch does not change that.
To match downstream in this aspect, adjust IEEE80211_PROBE_DELAY and/or
the 125ms max off-channel time in ieee80211_scan_state_decision.

[1]: commit d195d7aa ("wcn36xx: Ensure finish scan is not requested
before start scan") addressed one case of finish_scan_req being sent
without a preceding init_scan_req (the case of the operating channel
coinciding with the first scan channel); two other cases are:
1) if SW scan is started and aborted immediately, without scanning any
   channels, we send a finish_scan_req without ever sending init_scan_req,
   and
2) as SW scan logic always returns us to the operating channel before
   calling wcn36xx_sw_scan_complete, finish_scan_req is always sent twice
   at the end of a SW scan

Fixes: 8e84c258 ("wcn36xx: mac80211 driver for Qualcomm WCN3660/WCN3680 hardware")
Signed-off-by: Benjamin Li <benl@squareup.com>
Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211027170306.555535-4-benl@squareup.com

drivers/net/wireless/ath/wcn36xx/main.c

@@ -402,6 +402,7 @@ static void wcn36xx_change_opchannel(struct wcn36xx *wcn, int ch)
 static int wcn36xx_config(struct ieee80211_hw *hw, u32 changed)
 {
 	struct wcn36xx *wcn = hw->priv;
+	int ret;
 
 	wcn36xx_dbg(WCN36XX_DBG_MAC, "mac config changed 0x%08x\n", changed);
 
@@ -417,17 +418,31 @@ static int wcn36xx_config(struct ieee80211_hw *hw, u32 changed)
 			 * want to receive/transmit regular data packets, then
 			 * simply stop the scan session and exit PS mode.
 			 */
+			if (wcn->sw_scan_channel)
+				wcn36xx_smd_end_scan(wcn, wcn->sw_scan_channel);
+			if (wcn->sw_scan_init) {
 				wcn36xx_smd_finish_scan(wcn, HAL_SYS_MODE_SCAN,
 							wcn->sw_scan_vif);
-			wcn->sw_scan_channel = 0;
+			}
 		} else if (wcn->sw_scan) {
 			/* A scan is ongoing, do not change the operating
 			 * channel, but start a scan session on the channel.
 			 */
-			wcn36xx_smd_init_scan(wcn, HAL_SYS_MODE_SCAN,
+			if (wcn->sw_scan_channel)
+				wcn36xx_smd_end_scan(wcn, wcn->sw_scan_channel);
+			if (!wcn->sw_scan_init) {
+				/* This can fail if we are unable to notify the
+				 * operating channel.
+				 */
+				ret = wcn36xx_smd_init_scan(wcn,
+							    HAL_SYS_MODE_SCAN,
 							    wcn->sw_scan_vif);
+				if (ret) {
+					mutex_unlock(&wcn->conf_mutex);
+					return -EIO;
+				}
+			}
 			wcn36xx_smd_start_scan(wcn, ch);
-			wcn->sw_scan_channel = ch;
 		} else {
 			wcn36xx_change_opchannel(wcn, ch);
 		}
@@ -726,7 +741,12 @@ static void wcn36xx_sw_scan_complete(struct ieee80211_hw *hw,
 	wcn36xx_dbg(WCN36XX_DBG_MAC, "sw_scan_complete");
 
 	/* ensure that any scan session is finished */
-	wcn36xx_smd_finish_scan(wcn, HAL_SYS_MODE_SCAN, wcn->sw_scan_vif);
+	if (wcn->sw_scan_channel)
+		wcn36xx_smd_end_scan(wcn, wcn->sw_scan_channel);
+	if (wcn->sw_scan_init) {
+		wcn36xx_smd_finish_scan(wcn, HAL_SYS_MODE_SCAN,
+					wcn->sw_scan_vif);
+	}
 	wcn->sw_scan = false;
 	wcn->sw_scan_opchannel = 0;
 }

drivers/net/wireless/ath/wcn36xx/smd.c

@@ -722,6 +722,7 @@ int wcn36xx_smd_init_scan(struct wcn36xx *wcn, enum wcn36xx_hal_sys_mode mode,
 		wcn36xx_err("hal_init_scan response failed err=%d\n", ret);
 		goto out;
 	}
+	wcn->sw_scan_init = true;
 out:
 	mutex_unlock(&wcn->hal_mutex);
 	return ret;
@@ -752,6 +753,7 @@ int wcn36xx_smd_start_scan(struct wcn36xx *wcn, u8 scan_channel)
 		wcn36xx_err("hal_start_scan response failed err=%d\n", ret);
 		goto out;
 	}
+	wcn->sw_scan_channel = scan_channel;
 out:
 	mutex_unlock(&wcn->hal_mutex);
 	return ret;
@@ -782,6 +784,7 @@ int wcn36xx_smd_end_scan(struct wcn36xx *wcn, u8 scan_channel)
 		wcn36xx_err("hal_end_scan response failed err=%d\n", ret);
 		goto out;
 	}
+	wcn->sw_scan_channel = 0;
 out:
 	mutex_unlock(&wcn->hal_mutex);
 	return ret;
@@ -823,6 +826,7 @@ int wcn36xx_smd_finish_scan(struct wcn36xx *wcn,
 		wcn36xx_err("hal_finish_scan response failed err=%d\n", ret);
 		goto out;
 	}
+	wcn->sw_scan_init = false;
 out:
 	mutex_unlock(&wcn->hal_mutex);
 	return ret;

drivers/net/wireless/ath/wcn36xx/wcn36xx.h

@@ -248,6 +248,7 @@ struct wcn36xx {
 	struct cfg80211_scan_request *scan_req;
 	bool			sw_scan;
 	u8			sw_scan_opchannel;
+	bool			sw_scan_init;
 	u8			sw_scan_channel;
 	struct ieee80211_vif	*sw_scan_vif;
 	struct mutex		scan_lock;