From 3cb0272c8ee00baeea38c8342784b3ad9ac6433e Mon Sep 17 00:00:00 2001
From: hselasky <hselasky@ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f>
Date: Wed, 19 Nov 2014 09:07:49 +0000
Subject: [PATCH] MFC r274376: Fix some minor TSO issues: - Improve description
 of TSO limits. - Remove a not needed KASSERT() - Remove some not needed
 variable casts.

Sponsored by:	Mellanox Technologies


git-svn-id: svn://svn.freebsd.org/base/stable/9@274705 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
---
 sys/net/if.c             |  7 -------
 sys/net/if_var.h         | 23 ++++++++++++++++++-----
 sys/netinet/tcp_output.c | 16 ++++++++--------
 3 files changed, 26 insertions(+), 20 deletions(-)

diff --git a/sys/net/if.c b/sys/net/if.c
index 8711a8d9b..84346c698 100644
--- a/sys/net/if.c
+++ b/sys/net/if.c
@@ -747,13 +747,6 @@ if_attach_internal(struct ifnet *ifp, int vmove)
 				    ifp->if_hw_tsomaxsegsize);
 			}
 		}
-		/*
-		 * If the "if_hw_tsomax" limit is set, check if it is
-		 * too small:
-		 */
-		KASSERT(ifp->if_hw_tsomax == 0 ||
-		    ifp->if_hw_tsomax >= (IP_MAXPACKET / 8),
-		    ("%s: if_hw_tsomax is outside of range", __func__));
 #endif
 	}
 #ifdef VIMAGE
diff --git a/sys/net/if_var.h b/sys/net/if_var.h
index e40dae0a3..4119a007e 100644
--- a/sys/net/if_var.h
+++ b/sys/net/if_var.h
@@ -211,11 +211,24 @@ struct ifnet {
 	 * be used with care where binary compatibility is required.
 	 */
 	char	if_cspare[3];
-	u_int	if_hw_tsomax;		/* TSO total burst length
-					 * limit in bytes. A value of
-					 * zero means no limit. Have
-					 * to find a better place for
-					 * it eventually. */
+
+	/*
+	 * Network adapter TSO limits:
+	 * ===========================
+	 *
+	 * If the "if_hw_tsomax" field is zero the maximum segment
+	 * length limit does not apply. If the "if_hw_tsomaxsegcount"
+	 * or the "if_hw_tsomaxsegsize" field is zero the TSO segment
+	 * count limit does not apply. If all three fields are zero,
+	 * there is no TSO limit.
+	 *
+	 * NOTE: The TSO limits only apply to the data payload part of
+	 * a TCP/IP packet. That means there is no need to subtract
+	 * space for ethernet-, vlan-, IP- or TCP- headers from the
+	 * TSO limits unless the hardware driver in question requires
+	 * so.
+	 */
+	u_int	if_hw_tsomax;
 	int	if_ispare[1];
 	/*
 	 * TSO fields for segment limits. If a field is zero below,
diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index 98ea9c943..01253d3ab 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -794,9 +794,9 @@ send:
 				max_len = (if_hw_tsomax - hdrlen);
 				if (max_len <= 0) {
 					len = 0;
-				} else if (len > (u_int)max_len) {
+				} else if (len > max_len) {
 					sendalot = 1;
-					len = (u_int)max_len;
+					len = max_len;
 				}
 			}
 
@@ -809,7 +809,7 @@ send:
 				max_len = 0;
 				mb = sbsndmbuf(&so->so_snd, off, &moff);
 
-				while (mb != NULL && (u_int)max_len < len) {
+				while (mb != NULL && max_len < len) {
 					u_int mlen;
 					u_int frags;
 
@@ -843,9 +843,9 @@ send:
 				}
 				if (max_len <= 0) {
 					len = 0;
-				} else if (len > (u_int)max_len) {
+				} else if (len > max_len) {
 					sendalot = 1;
-					len = (u_int)max_len;
+					len = max_len;
 				}
 			}
 
@@ -856,7 +856,7 @@ send:
 			 */
 			max_len = (tp->t_maxopd - optlen);
 			if ((off + len) < so->so_snd.sb_cc) {
-				moff = len % (u_int)max_len;
+				moff = len % max_len;
 				if (moff != 0) {
 					len -= moff;
 					sendalot = 1;
@@ -867,8 +867,8 @@ send:
 			 * In case there are too many small fragments
 			 * don't use TSO:
 			 */
-			if (len <= (u_int)max_len) {
-				len = (u_int)max_len;
+			if (len <= max_len) {
+				len = max_len;
 				sendalot = 1;
 				tso = 0;
 			}
-- 
2.45.0