[PATCH rtw-next v7 3/3] wifi: rtw88: time the countdown downloads from the TBTT

[Mehmet Fide <mehmet.fide@gmail.com>]

From: Mehmet Fide <mehmet.fide@screeningeagle.com>

The countdown downloads are queued one beacon interval apart, with no
relation to the TBTT. A download that runs late past the next TBTT
leaves a count out of the air.

Queue each download 10 ms after the next TBTT, read from the TSF, so it
may run late by almost a beacon interval; a later one is followed by
the next at once. A TSF jump, an IBSS merge or a reset, restarts the
schedule from the next TBTT.

A TBTT just before the start may already have sent the first count; it
is taken as the one that did, so no count is sent twice.

The USB chips raise no TBTT interrupt, so the TSF register is read. The
beaconing interface is always on port 0: rtw_core_port_switch() moves
an AP there, an IBSS runs alone.

Signed-off-by: Mehmet Fide <mehmet.fide@screeningeagle.com>
---

Notes:
    Changes in v7:
    - new patch, from Ping-Ke's review of the countdown pacing in v6

 drivers/net/wireless/realtek/rtw88/fw.c   | 40 ++++++++++++++++++++---
 drivers/net/wireless/realtek/rtw88/main.h |  2 +-
 drivers/net/wireless/realtek/rtw88/reg.h  |  1 +
 3 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/fw.c b/drivers/net/wireless/realtek/rtw88/fw.c
index 2d81aaeed0d7..c5a106a59540 100644
--- a/drivers/net/wireless/realtek/rtw88/fw.c
+++ b/drivers/net/wireless/realtek/rtw88/fw.c
@@ -3,6 +3,7 @@
  */
 
 #include <linux/iopoll.h>
+#include <linux/math64.h>
 
 #include "main.h"
 #include "coex.h"
@@ -1809,27 +1810,58 @@ bool rtw_fw_csa_active(struct rtw_dev *rtwdev)
 	return !!rtwdev->csa_vif;
 }
 
-/* paced from the first download: a late one does not delay the next */
+#define RTW_CSA_TBTT_MARGIN_US	10000
+
+/* the beaconing interface is always on port 0 */
+static u64 rtw_fw_read_tsf(struct rtw_dev *rtwdev)
+{
+	u32 hi, lo;
+
+	do {
+		hi = rtw_read32(rtwdev, REG_TSFTR + 4);
+		lo = rtw_read32(rtwdev, REG_TSFTR);
+	} while (hi != rtw_read32(rtwdev, REG_TSFTR + 4));
+
+	return ((u64)hi << 32) | lo;
+}
+
 static void rtw_fw_csa_queue(struct rtw_dev *rtwdev, struct ieee80211_vif *vif)
 {
 	u32 interval = ieee80211_tu_to_usec(vif->bss_conf.beacon_int);
+	u64 tsf = rtw_fw_read_tsf(rtwdev);
 	s64 delay;
+	u32 rem;
 
-	rtwdev->csa_due = ktime_add_us(rtwdev->csa_due, interval);
-	delay = ktime_us_delta(rtwdev->csa_due, ktime_get());
+	rtwdev->csa_tbtt += interval;
+	delay = rtwdev->csa_tbtt + RTW_CSA_TBTT_MARGIN_US - tsf;
+	if (delay > interval + RTW_CSA_TBTT_MARGIN_US ||
+	    delay < -(s64)interval) {
+		/* the TSF jumped: restart from the next TBTT */
+		div_u64_rem(tsf, interval, &rem);
+		rtwdev->csa_tbtt = tsf - rem + interval;
+		delay = rtwdev->csa_tbtt + RTW_CSA_TBTT_MARGIN_US - tsf;
+	}
 	ieee80211_queue_delayed_work(rtwdev->hw, &rtwdev->csa_beacon_work,
 				     usecs_to_jiffies(max(delay, 0)));
 }
 
 void rtw_fw_csa_start(struct rtw_dev *rtwdev, struct ieee80211_vif *vif)
 {
+	u32 interval = ieee80211_tu_to_usec(vif->bss_conf.beacon_int);
+	u32 rem;
+
 	lockdep_assert_held(&rtwdev->mutex);
 
 	if (rtwdev->csa_vif == vif)
 		return;
 
 	rtwdev->csa_vif = vif;
-	rtwdev->csa_due = ktime_get();
+	rtwdev->csa_tbtt = rtw_fw_read_tsf(rtwdev);
+	div_u64_rem(rtwdev->csa_tbtt, interval, &rem);
+	rtwdev->csa_tbtt -= rem;
+	/* a TBTT that just passed may have sent the first count already */
+	if (rem < RTW_CSA_TBTT_MARGIN_US)
+		rtwdev->csa_tbtt -= interval;
 	rtw_fw_csa_queue(rtwdev, vif);
 }
 
diff --git a/drivers/net/wireless/realtek/rtw88/main.h b/drivers/net/wireless/realtek/rtw88/main.h
index bc3ebfec11ae..3be0a96d1186 100644
--- a/drivers/net/wireless/realtek/rtw88/main.h
+++ b/drivers/net/wireless/realtek/rtw88/main.h
@@ -2096,7 +2096,7 @@ struct rtw_dev {
 	struct work_struct update_beacon_work;
 	struct delayed_work csa_beacon_work;
 	struct ieee80211_vif *csa_vif;
-	ktime_t csa_due;
+	u64 csa_tbtt;
 
 	/* used to protect txqs list */
 	spinlock_t txq_lock;
diff --git a/drivers/net/wireless/realtek/rtw88/reg.h b/drivers/net/wireless/realtek/rtw88/reg.h
index afcdb66fdb9a..3ff4ae0885ef 100644
--- a/drivers/net/wireless/realtek/rtw88/reg.h
+++ b/drivers/net/wireless/realtek/rtw88/reg.h
@@ -506,6 +506,7 @@
 #define REG_USTIME_TSF		0x055C
 #define REG_BCN_MAX_ERR		0x055D
 #define REG_RXTSF_OFFSET_CCK	0x055E
+#define REG_TSFTR		0x0560
 #define REG_MISC_CTRL		0x0577
 #define BIT_EN_FREE_CNT		BIT(3)
 #define BIT_DIS_SECOND_CCA	(BIT(0) | BIT(1))
-- 
2.55.0