[PATCH] wifi: mt76: mt7603: add debugfs attr for disabling frames buffering

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

MT7603EN and MT7628AN were reported by multiple users to be unstable
under high traffic. Transmission of packets could stop for seconds often
leading to disconnections.

Long research & debugging revelaed a close relation between MCU
interrupts of type PKT_TYPE_TXS and slowdowns / stalls. That led to
questioning frames buffering feature.

It turns out that disabling SKBs loopback code makes mt7603 devices much
more stable under load. There are still some traffic hiccups but those
happen like once every an hour and end up in recovery in most cases.

Add a debugfs option for disabling frames buffering so users can give it
a try. If this solution yields a success we can make this feature
disabled by default.

This change was successfully tested using 2 GHz AP interface on:
1. Netgear R6220 - MT7621ST (SoC) + MT7603EN (WiFi) + MT7612EN (WiFi)
2. Xiaomi Mi Router 4C - MT7628AN (Wi-Fi SoC)

Link: https://lore.kernel.org/linux-wireless/7c96d5ee-86c1-8068-1b58-40db6087a24f@gmail.com/
Closes: https://github.com/openwrt/mt76/issues/865
Fixes: c8846e101502 ("mt76: add driver for MT7603E and MT7628/7688")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
 drivers/net/wireless/mediatek/mt76/mt7603/debugfs.c | 2 ++
 drivers/net/wireless/mediatek/mt76/mt7603/dma.c     | 3 +++
 drivers/net/wireless/mediatek/mt76/mt7603/init.c    | 1 +
 drivers/net/wireless/mediatek/mt76/mt7603/mt7603.h  | 2 ++
 4 files changed, 8 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/mt7603/debugfs.c b/drivers/net/wireless/mediatek/mt76/mt7603/debugfs.c
index 3967f2f05774..c80baba7a402 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7603/debugfs.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7603/debugfs.c
@@ -115,4 +115,6 @@ void mt7603_init_debugfs(struct mt7603_dev *dev)
 			    &dev->sensitivity_limit);
 	debugfs_create_bool("dynamic_sensitivity", 0600, dir,
 			    &dev->dynamic_sensitivity);
+	debugfs_create_bool("frames_buffering", 0600, dir,
+			    &dev->frames_buffering);
 }
diff --git a/drivers/net/wireless/mediatek/mt76/mt7603/dma.c b/drivers/net/wireless/mediatek/mt76/mt7603/dma.c
index 7a2f5d38562b..f5ab729dec31 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7603/dma.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7603/dma.c
@@ -27,6 +27,9 @@ mt7603_rx_loopback_skb(struct mt7603_dev *dev, struct sk_buff *skb)
 	u32 val;
 	u8 tid = 0;
 
+	if (!dev->frames_buffering)
+		goto free;
+
 	if (skb->len < MT_TXD_SIZE + sizeof(struct ieee80211_hdr))
 		goto free;
 
diff --git a/drivers/net/wireless/mediatek/mt76/mt7603/init.c b/drivers/net/wireless/mediatek/mt76/mt7603/init.c
index 6c55c72f28a2..5abc2618ec8b 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7603/init.c
+++ b/drivers/net/wireless/mediatek/mt76/mt7603/init.c
@@ -515,6 +515,7 @@ int mt7603_register_device(struct mt7603_dev *dev)
 	dev->slottime = 9;
 	dev->sensitivity_limit = 28;
 	dev->dynamic_sensitivity = true;
+	dev->frames_buffering = true;
 
 	ret = mt7603_init_hardware(dev);
 	if (ret)
diff --git a/drivers/net/wireless/mediatek/mt76/mt7603/mt7603.h b/drivers/net/wireless/mediatek/mt76/mt7603/mt7603.h
index 9e58df7042ad..02c88334cdc0 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7603/mt7603.h
+++ b/drivers/net/wireless/mediatek/mt76/mt7603/mt7603.h
@@ -155,6 +155,8 @@ struct mt7603_dev {
 	u32 reset_test;
 
 	unsigned int reset_cause[__RESET_CAUSE_MAX];
+
+	bool frames_buffering;
 };
 
 extern const struct mt76_driver_ops mt7603_drv_ops;
-- 
2.35.3