[PATCH v3 2/4] net: emac: implement TCP segmentation offload (TSO)

[Christian Lamparter <chunkeey@gmail.com>]

This patch enables TSO(v4) hw feature for emac driver.
As atleast the APM82181's TCP/IP acceleration hardware
controller (TAH) provides TCP segmentation support in
the transmit path.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
---
 drivers/net/ethernet/ibm/emac/core.c | 112 ++++++++++++++++++++++++++-
 drivers/net/ethernet/ibm/emac/core.h |   7 ++
 drivers/net/ethernet/ibm/emac/emac.h |   7 ++
 drivers/net/ethernet/ibm/emac/tah.c  |  22 +++++-
 drivers/net/ethernet/ibm/emac/tah.h  |   2 +
 5 files changed, 148 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
index be560f9031f4..80aafd7552aa 100644
--- a/drivers/net/ethernet/ibm/emac/core.c
+++ b/drivers/net/ethernet/ibm/emac/core.c
@@ -38,6 +38,9 @@
 #include <linux/mii.h>
 #include <linux/bitops.h>
 #include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
 #include <linux/workqueue.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
@@ -1118,6 +1121,32 @@ static int emac_resize_rx_ring(struct emac_instance *dev, int new_mtu)
 	return ret;
 }
 
+/* Restriction applied for the segmentation size
+ * to use HW segmentation offload feature. the size
+ * of the segment must not be less than 168 bytes for
+ * DIX formatted segments, or 176 bytes for
+ * IEEE formatted segments. However based on actual
+ * tests any MTU less than 416 causes excessive retries
+ * due to TX FIFO underruns.
+ */
+const u32 tah_ss[TAH_NO_SSR] = { 1500, 1344, 1152, 960, 768, 416 };
+
+/* look-up matching segment size for the given mtu */
+static void emac_find_tso_ss_for_mtu(struct emac_instance *dev)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(tah_ss); i++) {
+		if (tah_ss[i] <= dev->ndev->mtu)
+			break;
+	}
+	/* if no matching segment size is found, set the tso_ss_mtu_start
+	 * variable anyway. This will cause the emac_tx_tso to skip straight
+	 * to the software fallback.
+	 */
+	dev->tso_ss_mtu_start = i;
+}
+
 /* Process ctx, rtnl_lock semaphore */
 static int emac_change_mtu(struct net_device *ndev, int new_mtu)
 {
@@ -1134,6 +1163,7 @@ static int emac_change_mtu(struct net_device *ndev, int new_mtu)
 
 	if (!ret) {
 		ndev->mtu = new_mtu;
+		emac_find_tso_ss_for_mtu(dev);
 		dev->rx_skb_size = emac_rx_skb_size(new_mtu);
 		dev->rx_sync_size = emac_rx_sync_size(new_mtu);
 	}
@@ -1410,6 +1440,33 @@ static inline u16 emac_tx_csum(struct emac_instance *dev,
 	return 0;
 }
 
+static int emac_tx_tso(struct emac_instance *dev, struct sk_buff *skb,
+		       u16 *ctrl)
+{
+	if (emac_has_feature(dev, EMAC_FTR_TAH_HAS_TSO) && skb_is_gso(skb) &&
+	    !!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))) {
+		u32 seg_size = 0, i;
+
+		/* Get the MTU */
+		seg_size = skb_shinfo(skb)->gso_size + tcp_hdrlen(skb) +
+			   skb_network_header_len(skb);
+
+		for (i = dev->tso_ss_mtu_start; i < ARRAY_SIZE(tah_ss); i++) {
+			if (tah_ss[i] > seg_size)
+				continue;
+
+			*ctrl |= EMAC_TX_CTRL_TAH_SSR(i);
+			return 0;
+		}
+
+		/* none found fall back to software */
+		return -EINVAL;
+	}
+
+	*ctrl |= emac_tx_csum(dev, skb);
+	return 0;
+}
+
 static inline netdev_tx_t emac_xmit_finish(struct emac_instance *dev, int len)
 {
 	struct emac_regs __iomem *p = dev->emacp;
@@ -1452,6 +1509,46 @@ static inline u16 emac_tx_vlan(struct emac_instance *dev, struct sk_buff *skb)
 	return 0;
 }
 
+static netdev_tx_t
+emac_start_xmit_sg(struct sk_buff *skb, struct net_device *ndev);
+
+static int
+emac_sw_tso(struct sk_buff *skb, struct net_device *ndev)
+{
+	struct emac_instance *dev = netdev_priv(ndev);
+	struct sk_buff *segs, *curr;
+	unsigned int i, frag_slots;
+
+	/* make sure to not overflow the tx ring */
+	frag_slots = dev->tx_cnt;
+	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+		struct skb_frag_struct *frag = &skb_shinfo(skb)->frags[i];
+
+		frag_slots += mal_tx_chunks(skb_frag_size(frag));
+
+		if (frag_slots >= NUM_TX_BUFF)
+			return -ENOSPC;
+	};
+
+	segs = skb_gso_segment(skb, ndev->features &
+					~(NETIF_F_TSO | NETIF_F_TSO6));
+	if (IS_ERR_OR_NULL(segs)) {
+		++dev->estats.tx_dropped;
+		dev_kfree_skb_any(skb);
+	} else {
+		while (segs) {
+			curr = segs;
+			segs = curr->next;
+			curr->next = NULL;
+
+			emac_start_xmit_sg(curr, ndev);
+		}
+		dev_consume_skb_any(skb);
+	}
+
+	return 0;
+}
+
 /* Tx lock BH */
 static netdev_tx_t emac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 {
@@ -1535,7 +1632,12 @@ emac_start_xmit_sg(struct sk_buff *skb, struct net_device *ndev)
 		goto stop_queue;
 
 	ctrl = EMAC_TX_CTRL_GFCS | EMAC_TX_CTRL_GP | MAL_TX_CTRL_READY |
-	    emac_tx_csum(dev, skb) | emac_tx_vlan(dev, skb);
+	    emac_tx_vlan(dev, skb);
+	if (emac_tx_tso(dev, skb, &ctrl)) {
+		if (emac_sw_tso(skb, ndev))
+			goto stop_queue;
+	}
+
 	slot = dev->tx_slot;
 
 	/* skb data */
@@ -2946,6 +3048,9 @@ static int emac_init_config(struct emac_instance *dev)
 	if (dev->tah_ph != 0) {
 #ifdef CONFIG_IBM_EMAC_TAH
 		dev->features |= EMAC_FTR_HAS_TAH;
+
+		if (of_device_is_compatible(np, "ibm,emac-apm821xx"))
+			dev->features |= EMAC_FTR_TAH_HAS_TSO;
 #else
 		printk(KERN_ERR "%pOF: TAH support not enabled !\n", np);
 		return -ENXIO;
@@ -3113,6 +3218,8 @@ static int emac_probe(struct platform_device *ofdev)
 	}
 	dev->rx_skb_size = emac_rx_skb_size(ndev->mtu);
 	dev->rx_sync_size = emac_rx_sync_size(ndev->mtu);
+	ndev->gso_max_segs = NUM_TX_BUFF / 2;
+	emac_find_tso_ss_for_mtu(dev);
 
 	/* Get pointers to BD rings */
 	dev->tx_desc =
@@ -3167,6 +3274,9 @@ static int emac_probe(struct platform_device *ofdev)
 	if (dev->tah_dev) {
 		ndev->hw_features = NETIF_F_IP_CSUM | NETIF_F_SG;
 
+		if (emac_has_feature(dev, EMAC_FTR_TAH_HAS_TSO))
+			ndev->hw_features |= NETIF_F_TSO;
+
 		if (emac_has_feature(dev, EMAC_FTR_HAS_VLAN_CTAG_TX)) {
 			ndev->vlan_features |= ndev->hw_features;
 			ndev->hw_features |= NETIF_F_HW_VLAN_CTAG_TX;
diff --git a/drivers/net/ethernet/ibm/emac/core.h b/drivers/net/ethernet/ibm/emac/core.h
index 8d84d439168c..0bcfe952a3cf 100644
--- a/drivers/net/ethernet/ibm/emac/core.h
+++ b/drivers/net/ethernet/ibm/emac/core.h
@@ -245,6 +245,9 @@ struct emac_instance {
 	u32				xaht_slots_shift;
 	u32				xaht_width_shift;
 
+	/* TAH TSO start index */
+	int				tso_ss_mtu_start;
+
 	/* Descriptor management
 	 */
 	struct mal_descriptor		*tx_desc;
@@ -336,6 +339,8 @@ struct emac_instance {
 #define EMAC_FTR_APM821XX_NO_HALF_DUPLEX	0x00001000
 /* EMAC can insert 802.1Q tag */
 #define EMAC_FTR_HAS_VLAN_CTAG_TX		0x00002000
+/* TAH can do TCP segmentation offload */
+#define EMAC_FTR_TAH_HAS_TSO			0x00004000
 
 /* Right now, we don't quite handle the always/possible masks on the
  * most optimal way as we don't have a way to say something like
@@ -352,6 +357,8 @@ enum {
 #endif
 #ifdef CONFIG_IBM_EMAC_TAH
 	    EMAC_FTR_HAS_TAH	|
+	    EMAC_FTR_TAH_HAS_TSO	|
+
 #endif
 #ifdef CONFIG_IBM_EMAC_ZMII
 	    EMAC_FTR_HAS_ZMII	|
diff --git a/drivers/net/ethernet/ibm/emac/emac.h b/drivers/net/ethernet/ibm/emac/emac.h
index e2f80cca9bed..833967aceb2f 100644
--- a/drivers/net/ethernet/ibm/emac/emac.h
+++ b/drivers/net/ethernet/ibm/emac/emac.h
@@ -266,6 +266,13 @@ struct emac_regs {
 #define EMAC_TX_CTRL_IVT		0x0020
 #define EMAC_TX_CTRL_RVT		0x0010
 #define EMAC_TX_CTRL_TAH_CSUM		0x000e
+#define EMAC_TX_CTRL_TAH_SSR(idx)	(((idx) + 1) << 1)
+#define EMAC_TX_CTRL_TAH_SSR5		0x000c
+#define EMAC_TX_CTRL_TAH_SSR4		0x000a
+#define EMAC_TX_CTRL_TAH_SSR3		0x0008
+#define EMAC_TX_CTRL_TAH_SSR2		0x0006
+#define EMAC_TX_CTRL_TAH_SSR1		0x0004
+#define EMAC_TX_CTRL_TAH_SSR0		0x0002
 
 /* EMAC specific TX descriptor status fields (read access) */
 #define EMAC_TX_ST_BFCS			0x0200
diff --git a/drivers/net/ethernet/ibm/emac/tah.c b/drivers/net/ethernet/ibm/emac/tah.c
index 9912456dca48..619c08ee22f7 100644
--- a/drivers/net/ethernet/ibm/emac/tah.c
+++ b/drivers/net/ethernet/ibm/emac/tah.c
@@ -45,6 +45,24 @@ void tah_detach(struct platform_device *ofdev, int channel)
 	mutex_unlock(&dev->lock);
 }
 
+static void tah_set_ssr(struct platform_device *ofdev)
+{
+	struct tah_instance *dev = dev_get_drvdata(&ofdev->dev);
+	struct tah_regs __iomem *p = dev->base;
+	int i;
+
+	mutex_lock(&dev->lock);
+
+	for (i = 0; i < ARRAY_SIZE(tah_ss); i++) {
+		/* Segment size can be up to 16K, but needs
+		 * to be a multiple of 2 bytes
+		 */
+		out_be32(&p->ssr0 + i, (tah_ss[i] & 0x3ffc) << 16);
+	}
+
+	mutex_unlock(&dev->lock);
+}
+
 void tah_reset(struct platform_device *ofdev)
 {
 	struct tah_instance *dev = platform_get_drvdata(ofdev);
@@ -64,6 +82,8 @@ void tah_reset(struct platform_device *ofdev)
 	out_be32(&p->mr,
 		 TAH_MR_CVR | TAH_MR_ST_768 | TAH_MR_TFS_10KB | TAH_MR_DTFP |
 		 TAH_MR_DIG);
+
+	tah_set_ssr(ofdev);
 }
 
 int tah_get_regs_len(struct platform_device *ofdev)
@@ -118,7 +138,7 @@ static int tah_probe(struct platform_device *ofdev)
 
 	platform_set_drvdata(ofdev, dev);
 
-	/* Initialize TAH and enable IPv4 checksum verification, no TSO yet */
+	/* Initialize TAH and enable IPv4 checksum verification */
 	tah_reset(ofdev);
 
 	printk(KERN_INFO "TAH %pOF initialized\n", ofdev->dev.of_node);
diff --git a/drivers/net/ethernet/ibm/emac/tah.h b/drivers/net/ethernet/ibm/emac/tah.h
index 4d5f336f07b3..2cb0629f30e2 100644
--- a/drivers/net/ethernet/ibm/emac/tah.h
+++ b/drivers/net/ethernet/ibm/emac/tah.h
@@ -36,6 +36,8 @@ struct tah_regs {
 	u32 tsr;
 };
 
+#define TAH_NO_SSR	6
+extern const u32 tah_ss[TAH_NO_SSR];
 
 /* TAH device */
 struct tah_instance {
-- 
2.19.1