i40e: Fix TSO with more than 8 frags per segment issue

The hardware has some limitations the driver needs to adhere to,
that we found in extended testing.
  1) no more than 8 descriptors per packet on the wire
  2) no header can span more than 3 descriptors

If one of these events occurs, the hardware will generate an internal
error and freeze the Tx queue.

This patch linearizes the skb to avoid these situations.

Change-ID: I37dab7d3966e14895a9663ec4d0aaa8eb0d9e115
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Jim Young <james.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_txrx.c

@@ -2139,6 +2139,67 @@ static int i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size)
 	return __i40e_maybe_stop_tx(tx_ring, size);
 }
 
+/**
+ * i40e_chk_linearize - Check if there are more than 8 fragments per packet
+ * @skb:      send buffer
+ * @tx_flags: collected send information
+ * @hdr_len:  size of the packet header
+ *
+ * Note: Our HW can't scatter-gather more than 8 fragments to build
+ * a packet on the wire and so we need to figure out the cases where we
+ * need to linearize the skb.
+ **/
+static bool i40e_chk_linearize(struct sk_buff *skb, u32 tx_flags,
+			       const u8 hdr_len)
+{
+	struct skb_frag_struct *frag;
+	bool linearize = false;
+	unsigned int size = 0;
+	u16 num_frags;
+	u16 gso_segs;
+
+	num_frags = skb_shinfo(skb)->nr_frags;
+	gso_segs = skb_shinfo(skb)->gso_segs;
+
+	if (tx_flags & (I40E_TX_FLAGS_TSO | I40E_TX_FLAGS_FSO)) {
+		u16 j = 1;
+
+		if (num_frags < (I40E_MAX_BUFFER_TXD))
+			goto linearize_chk_done;
+		/* try the simple math, if we have too many frags per segment */
+		if (DIV_ROUND_UP((num_frags + gso_segs), gso_segs) >
+		    I40E_MAX_BUFFER_TXD) {
+			linearize = true;
+			goto linearize_chk_done;
+		}
+		frag = &skb_shinfo(skb)->frags[0];
+		size = hdr_len;
+		/* we might still have more fragments per segment */
+		do {
+			size += skb_frag_size(frag);
+			frag++; j++;
+			if (j == I40E_MAX_BUFFER_TXD) {
+				if (size < skb_shinfo(skb)->gso_size) {
+					linearize = true;
+					break;
+				}
+				j = 1;
+				size -= skb_shinfo(skb)->gso_size;
+				if (size)
+					j++;
+				size += hdr_len;
+			}
+			num_frags--;
+		} while (num_frags);
+	} else {
+		if (num_frags >= I40E_MAX_BUFFER_TXD)
+			linearize = true;
+	}
+
+linearize_chk_done:
+	return linearize;
+}
+
 /**
  * i40e_tx_map - Build the Tx descriptor
  * @tx_ring:  ring to send buffer on
@@ -2396,6 +2457,10 @@ static netdev_tx_t i40e_xmit_frame_ring(struct sk_buff *skb,
 	if (tsyn)
 		tx_flags |= I40E_TX_FLAGS_TSYN;
 
+	if (i40e_chk_linearize(skb, tx_flags, hdr_len))
+		if (skb_linearize(skb))
+			goto out_drop;
+
 	skb_tx_timestamp(skb);
 
 	/* always enable CRC insertion offload */

drivers/net/ethernet/intel/i40e/i40e_txrx.h

@@ -112,6 +112,7 @@ enum i40e_dyn_idx_t {
 
 #define i40e_rx_desc i40e_32byte_rx_desc
 
+#define I40E_MAX_BUFFER_TXD	8
 #define I40E_MIN_TX_LEN		17
 #define I40E_MAX_DATA_PER_TXD	8192
 

drivers/net/ethernet/intel/i40evf/i40e_txrx.c

@@ -1380,6 +1380,67 @@ static void i40e_create_tx_ctx(struct i40e_ring *tx_ring,
 	context_desc->type_cmd_tso_mss = cpu_to_le64(cd_type_cmd_tso_mss);
 }
 
+ /**
+ * i40e_chk_linearize - Check if there are more than 8 fragments per packet
+ * @skb:      send buffer
+ * @tx_flags: collected send information
+ * @hdr_len:  size of the packet header
+ *
+ * Note: Our HW can't scatter-gather more than 8 fragments to build
+ * a packet on the wire and so we need to figure out the cases where we
+ * need to linearize the skb.
+ **/
+static bool i40e_chk_linearize(struct sk_buff *skb, u32 tx_flags,
+			       const u8 hdr_len)
+{
+	struct skb_frag_struct *frag;
+	bool linearize = false;
+	unsigned int size = 0;
+	u16 num_frags;
+	u16 gso_segs;
+
+	num_frags = skb_shinfo(skb)->nr_frags;
+	gso_segs = skb_shinfo(skb)->gso_segs;
+
+	if (tx_flags & (I40E_TX_FLAGS_TSO | I40E_TX_FLAGS_FSO)) {
+		u16 j = 1;
+
+		if (num_frags < (I40E_MAX_BUFFER_TXD))
+			goto linearize_chk_done;
+		/* try the simple math, if we have too many frags per segment */
+		if (DIV_ROUND_UP((num_frags + gso_segs), gso_segs) >
+		    I40E_MAX_BUFFER_TXD) {
+			linearize = true;
+			goto linearize_chk_done;
+		}
+		frag = &skb_shinfo(skb)->frags[0];
+		size = hdr_len;
+		/* we might still have more fragments per segment */
+		do {
+			size += skb_frag_size(frag);
+			frag++; j++;
+			if (j == I40E_MAX_BUFFER_TXD) {
+				if (size < skb_shinfo(skb)->gso_size) {
+					linearize = true;
+					break;
+				}
+				j = 1;
+				size -= skb_shinfo(skb)->gso_size;
+				if (size)
+					j++;
+				size += hdr_len;
+			}
+			num_frags--;
+		} while (num_frags);
+	} else {
+		if (num_frags >= I40E_MAX_BUFFER_TXD)
+			linearize = true;
+	}
+
+linearize_chk_done:
+	return linearize;
+}
+
 /**
  * i40e_tx_map - Build the Tx descriptor
  * @tx_ring:  ring to send buffer on
@@ -1654,6 +1715,10 @@ static netdev_tx_t i40e_xmit_frame_ring(struct sk_buff *skb,
 	else if (tso)
 		tx_flags |= I40E_TX_FLAGS_TSO;
 
+	if (i40e_chk_linearize(skb, tx_flags, hdr_len))
+		if (skb_linearize(skb))
+			goto out_drop;
+
 	skb_tx_timestamp(skb);
 
 	/* always enable CRC insertion offload */

drivers/net/ethernet/intel/i40evf/i40e_txrx.h

@@ -112,6 +112,7 @@ enum i40e_dyn_idx_t {
 
 #define i40e_rx_desc i40e_32byte_rx_desc
 
+#define I40E_MAX_BUFFER_TXD	8
 #define I40E_MIN_TX_LEN		17
 #define I40E_MAX_DATA_PER_TXD	8192