net: Introduce NETIF_F_GRO_HW.

Introduce NETIF_F_GRO_HW feature flag for NICs that support hardware
GRO.  With this flag, we can now independently turn on or off hardware
GRO when GRO is on.  Previously, drivers were using NETIF_F_GRO to
control hardware GRO and so it cannot be independently turned on or
off without affecting GRO.

Hardware GRO (just like GRO) guarantees that packets can be re-segmented
by TSO/GSO to reconstruct the original packet stream.  Logically,
GRO_HW should depend on GRO since it a subset, but we will let
individual drivers enforce this dependency as they see fit.

Since NETIF_F_GRO is not propagated between upper and lower devices,
NETIF_F_GRO_HW should follow suit since it is a subset of GRO.  In other
words, a lower device can independent have GRO/GRO_HW enabled or disabled
and no feature propagation is required.  This will preserve the current
GRO behavior.  This can be changed later if we decide to propagate GRO/
GRO_HW/RXCSUM from upper to lower devices.

Cc: Ariel Elior <Ariel.Elior@cavium.com>
Cc: everest-linux-l2@cavium.com
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/netdev-features.txt

@@ -163,3 +163,12 @@ This requests that the NIC receive all possible frames, including errored
 frames (such as bad FCS, etc).  This can be helpful when sniffing a link with
 bad packets on it.  Some NICs may receive more packets if also put into normal
 PROMISC mode.
+
+*  rx-gro-hw
+
+This requests that the NIC enables Hardware GRO (generic receive offload).
+Hardware GRO is basically the exact reverse of TSO, and is generally
+stricter than Hardware LRO.  A packet stream merged by Hardware GRO must
+be re-segmentable by GSO or TSO back to the exact original packet stream.
+Hardware GRO is dependent on RXCSUM since every packet successfully merged
+by hardware must also have the checksum verified by hardware.

include/linux/netdev_features.h

@@ -78,6 +78,8 @@ enum {
 	NETIF_F_HW_ESP_TX_CSUM_BIT,	/* ESP with TX checksum offload */
 	NETIF_F_RX_UDP_TUNNEL_PORT_BIT, /* Offload of RX port for UDP tunnels */
 
+	NETIF_F_GRO_HW_BIT,		/* Hardware Generic receive offload */
+
 	/*
 	 * Add your fresh new feature above and remember to update
 	 * netdev_features_strings[] in net/core/ethtool.c and maybe
@@ -97,6 +99,7 @@ enum {
 #define NETIF_F_FRAGLIST	__NETIF_F(FRAGLIST)
 #define NETIF_F_FSO		__NETIF_F(FSO)
 #define NETIF_F_GRO		__NETIF_F(GRO)
+#define NETIF_F_GRO_HW		__NETIF_F(GRO_HW)
 #define NETIF_F_GSO		__NETIF_F(GSO)
 #define NETIF_F_GSO_ROBUST	__NETIF_F(GSO_ROBUST)
 #define NETIF_F_HIGHDMA		__NETIF_F(HIGHDMA)

net/core/dev.c

@@ -7424,6 +7424,18 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
 		features &= ~dev->gso_partial_features;
 	}
 
+	if (!(features & NETIF_F_RXCSUM)) {
+		/* NETIF_F_GRO_HW implies doing RXCSUM since every packet
+		 * successfully merged by hardware must also have the
+		 * checksum verified by hardware.  If the user does not
+		 * want to enable RXCSUM, logically, we should disable GRO_HW.
+		 */
+		if (features & NETIF_F_GRO_HW) {
+			netdev_dbg(dev, "Dropping NETIF_F_GRO_HW since no RXCSUM feature.\n");
+			features &= ~NETIF_F_GRO_HW;
+		}
+	}
+
 	return features;
 }
 

net/core/ethtool.c

@@ -73,6 +73,7 @@ static const char netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN]
 	[NETIF_F_LLTX_BIT] =             "tx-lockless",
 	[NETIF_F_NETNS_LOCAL_BIT] =      "netns-local",
 	[NETIF_F_GRO_BIT] =              "rx-gro",
+	[NETIF_F_GRO_HW_BIT] =           "rx-gro-hw",
 	[NETIF_F_LRO_BIT] =              "rx-lro",
 
 	[NETIF_F_TSO_BIT] =              "tx-tcp-segmentation",