ath10k: make hw roc more reliable

With P2P concurrency requested hw roc duration
time can be very small. Some firmware revisions
refuse scan requests with too small channel dwell
time.

This prevents messages like, e.g. with connected
STA vif and performing P2P Find:

 ath10k_pci 0000:00:05.0: failed to switch to channel for roc scan
 ieee80211 phy3: failed to start next HW ROC (-110)
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath10k/mac.c

@@ -3848,6 +3848,8 @@ static int ath10k_remain_on_channel(struct ieee80211_hw *hw,
 	if (ret)
 		goto exit;
 
+	duration = max(duration, WMI_SCAN_CHAN_MIN_TIME_MSEC);
+
 	memset(&arg, 0, sizeof(arg));
 	ath10k_wmi_start_scan_init(ar, &arg);
 	arg.vdev_id = arvif->vdev_id;

drivers/net/wireless/ath/ath10k/wmi.h

@@ -1952,6 +1952,11 @@ struct wmi_ssid_list {
 #define WLAN_SCAN_PARAMS_MAX_BSSID   4
 #define WLAN_SCAN_PARAMS_MAX_IE_LEN  256
 
+/* Values lower than this may be refused by some firmware revisions with a scan
+ * completion with a timedout reason.
+ */
+#define WMI_SCAN_CHAN_MIN_TIME_MSEC 40
+
 /* Scan priority numbers must be sequential, starting with 0 */
 enum wmi_scan_priority {
 	WMI_SCAN_PRIORITY_VERY_LOW = 0,