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>

2 files changed, 66 insertions, 0 deletions

diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
index 29004382f462..1320a433b8ed 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
+++ b/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 */
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
index 4e15903b2b6d..c950a038237c 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
+++ b/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