mac80211: allow drivers to support S/G

If drivers want to support S/G (really just gather DMA on TX) then
we can now easily support this on the fast-xmit path since it just
needs to write to the ethernet header (and already has a check for
that being possible.)

However, disallow this on the regular TX path (which has to handle
fragmentation, software crypto, etc.) by calling skb_linearize().

Also allow the related HIGHDMA since that's not interesting to the
code in mac80211 at all anyway.

Change-Id: I22edad610596a34761e4f1ae519f5fd31e0c8898
Signed-off-by: Johannes Berg <>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 2772578..a68beb8 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1941,8 +1941,8 @@
  *	Use the %IEEE80211_RADIOTAP_VHT_KNOWN_* values.
  * @netdev_features: netdev features to be set in each netdev created
- *	from this HW. Note only HW checksum features are currently
- *	compatible with mac80211. Other feature bits will be rejected.
+ *	from this HW. Note that not all features are usable with mac80211,
+ *	other features will be rejected during HW registration.
  * @uapsd_queues: This bitmap is included in (re)association frame to indicate
  *	for each access category if it is uAPSD trigger-enabled and delivery-
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index dde23c2..adb7ee8 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -840,7 +840,7 @@
 	/* Only HW csum features are currently compatible with mac80211 */
 	feature_whitelist = NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
-			    NETIF_F_HW_CSUM;
 	if (WARN_ON(hw->netdev_features & ~feature_whitelist))
 		return -EINVAL;
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 4ad6124..b8d613d 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2864,6 +2864,12 @@
 			goto out;
+	/* we cannot process non-linear frames on this path */
+	if (skb_linearize(skb)) {
+		kfree_skb(skb);
+		goto out;
+	}
 	/* the frame could be fragmented, software-encrypted, and other things
 	 * so we cannot really handle checksum offload with it - fix it up in
 	 * software before we handle anything else.