From 70fbcd451b68b7f6038d8a602cd8d5e1bb890f1d Mon Sep 17 00:00:00 2001
From: Damien Broka <git@damien.sh>
Date: Wed, 13 Sep 2023 09:23:47 +0100
Subject: [PATCH] axge: Skip dummy packet headers

Newer versions of the AX88179 interweave dummies alongside valid
packet headers in bulk IN transfer data. This was probably done for
backward compatibility with existing drivers.

However current driver records these dummy headers as dropped frames,
leading to stats misreporting one Ierr per Ipkt.

This skips those dummy headers silently, thereby not generating Ierrs
for them.

Reviewed by:	emaste
Pull Request:	https://github.com/freebsd/freebsd-src/pull/842
---
 sys/dev/usb/net/if_axge.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/sys/dev/usb/net/if_axge.c b/sys/dev/usb/net/if_axge.c
index a3b459a553e0..385a982afd9d 100644
--- a/sys/dev/usb/net/if_axge.c
+++ b/sys/dev/usb/net/if_axge.c
@@ -959,8 +959,16 @@ axge_rx_frame(struct usb_ether *ue, struct usb_page_cache *pc, int actlen)
 	hdr_off = pkt_end = (rxhdr >> 16) & 0xFFFF;
 
 	/*
+	 * On older firmware:
 	 * <----------------------- actlen ------------------------>
 	 * [frame #0]...[frame #N][pkt_hdr #0]...[pkt_hdr #N][rxhdr]
+	 *
+	 * On newer firmware:
+	 * <----------------------- actlen -----------------
+	 * [frame #0]...[frame #N][pkt_hdr #0][dummy_hdr]...
+	 *                         -------------------------------->
+	 *                         ...[pkt_hdr #N][dummy_hdr][rxhdr]
+	 *
 	 * Each RX frame would be aligned on 8 bytes boundary. If
 	 * RCR_IPE bit is set in AXGE_RCR register, there would be 2
 	 * padding bytes and 6 dummy bytes(as the padding also should
@@ -968,6 +976,10 @@ axge_rx_frame(struct usb_ether *ue, struct usb_page_cache *pc, int actlen)
 	 * IP header on 32bits boundary.  Driver don't set RCR_IPE bit
 	 * of AXGE_RCR register, so there should be no padding bytes
 	 * which simplifies RX logic a lot.
+	 *
+	 * Further, newer firmware interweaves dummy headers that have
+	 * pktlen == 0 and should be skipped without being seen as
+	 * dropped frames.
 	 */
 	while (pkt_cnt--) {
 		/* verify the header offset */
@@ -978,6 +990,12 @@ axge_rx_frame(struct usb_ether *ue, struct usb_page_cache *pc, int actlen)
 		usbd_copy_out(pc, hdr_off, &pkt_hdr, sizeof(pkt_hdr));
 		pkt_hdr.status = le32toh(pkt_hdr.status);
 		pktlen = AXGE_RXBYTES(pkt_hdr.status);
+		hdr_off += sizeof(pkt_hdr);
+
+		/* Skip dummy packet header. */
+		if (pktlen == 0)
+			continue;
+
 		if (pos + pktlen > pkt_end) {
 			DPRINTF("Data position reached end\n");
 			break;
@@ -989,7 +1007,6 @@ axge_rx_frame(struct usb_ether *ue, struct usb_page_cache *pc, int actlen)
 		} else
 			axge_rxeof(ue, pc, pos, pktlen, pkt_hdr.status);
 		pos += (pktlen + 7) & ~7;
-		hdr_off += sizeof(pkt_hdr);
 	}
 }