[PATCH rtw-next v2 2/3] wifi: rtw88: usb: only let the frames a dozing station needs use the after-DTIM queue

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

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

With the budget in place the high queue can no longer take the chip
down, but ordinary chatter still competes with the frames a sleeping
station actually needs. mac80211 marks every broadcast and multicast
frame with IEEE80211_TX_CTL_SEND_AFTER_DTIM while a station dozes,
mDNS and SSDP included, so under normal traffic the budget is spent on
frames nobody waits for.

Do what the vendor driver does with its default "allow special" high
queue filter: admit only ARP, EAPOL and DHCP to the after-DTIM path,
the frames a station coming out of power save has to see; everything
else goes out on its access category queue at line rate. The frames
are classified the way rtw89_core_tx_btc_spec_pkt_notify() does it,
from skb->protocol and the network and transport header offsets that
mac80211 keeps from the netdev path; EAPOL is the control port flag.
Frames the AP relays between its own stations arrive as ETH_P_802_3
and are not inspected, they leave on the access category queue.

With the filter in place the page pool stays at 1803 through the same
180 second storm, a DHCP flood still takes the after-DTIM path (and is
then held by the budget), and join/ping cycling without power save is
unchanged (10/10).

Signed-off-by: Mehmet Fide <mehmet.fide@screeningeagle.com>
---
v2:
- classify from skb->protocol, ip_hdr() and udp_hdr() like
  rtw89_core_tx_btc_spec_pkt_notify(), EAPOL from the control port flag;
  the SNAP/IV parser and linux/unaligned.h are gone (Ping-Ke)
- <linux/*> includes in alphabetical order (Ping-Ke)
- relayed (ETH_P_802_3) frames documented as not inspected

 drivers/net/wireless/realtek/rtw88/usb.c | 26 ++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
index 5482e44f4a88..473b63d16658 100644
--- a/drivers/net/wireless/realtek/rtw88/usb.c
+++ b/drivers/net/wireless/realtek/rtw88/usb.c
@@ -2,9 +2,11 @@
 /* Copyright(c) 2018-2019  Realtek Corporation
  */
 
+#include <linux/ip.h>
 #include <linux/module.h>
-#include <linux/usb.h>
 #include <linux/mutex.h>
+#include <linux/udp.h>
+#include <linux/usb.h>
 #include "main.h"
 #include "debug.h"
 #include "mac.h"
@@ -562,6 +564,26 @@ static int rtw_usb_write_data_h2c(struct rtw_dev *rtwdev, u8 *buf, u32 size)
 	return rtw_usb_write_data(rtwdev, &pkt_info, buf);
 }
 
+static bool rtw_usb_bmc_needs_dtim(struct sk_buff *skb)
+{
+	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
+	struct udphdr *udphdr;
+
+	if (info->control.flags & IEEE80211_TX_CTRL_PORT_CTRL_PROTO)
+		return true;
+
+	if (skb->protocol == htons(ETH_P_ARP))
+		return true;
+
+	if (skb->protocol != htons(ETH_P_IP) ||
+	    ip_hdr(skb)->protocol != IPPROTO_UDP)
+		return false;
+
+	udphdr = udp_hdr(skb);
+
+	return udphdr->dest == htons(67) || udphdr->dest == htons(68);
+}
+
 #define RTW_USB_HIQ_REFILL_INTERVAL	(HZ / 10)	/* jiffies per unit of budget */
 #define RTW_USB_HIQ_BUDGET_MAX		16
 
@@ -604,7 +626,7 @@ static u8 rtw_usb_tx_queue_mapping_to_qsel(struct rtw_usb *rtwusb,
 	else if (is_broadcast_ether_addr(hdr->addr1) ||
 		 is_multicast_ether_addr(hdr->addr1))
 		qsel = (info->flags & IEEE80211_TX_CTL_SEND_AFTER_DTIM) &&
-		       rtw_usb_hiq_take_budget(rtwusb) ?
+		       rtw_usb_bmc_needs_dtim(skb) && rtw_usb_hiq_take_budget(rtwusb) ?
 		       TX_DESC_QSEL_HIGH : skb->priority;
 	else if (skb_get_queue_mapping(skb) <= IEEE80211_AC_BK)
 		qsel = skb->priority;
-- 
2.55.0