To use the HW offloads capability (e.g. checksum and TSO) in the Tx
direction, the upper-layer users need to call rte_eth_dev_prepare to do
some adjustment to the packets before sending them (e.g. processing
pseudo headers when Tx checksum offoad enabled). But, the tx_prepare
callback of the bond driver is not implemented. Therefore, related
offloads can not be used unless the upper layer users process the packet
properly in their own application. But it is bad for the
transplantability.

However, it is difficult to design the tx_prepare callback for bonding
driver. Because when a bonded device sends packets, the bonded device
allocates the packets to different slave devices based on the real-time
link status and bonding mode. That is, it is very difficult for the
bonding device to determine which slave device's prepare function should
be invoked. In addition, if the link status changes after the packets are
prepared, the packets may fail to be sent because packets allocation may
change.

So, in this patch, the tx_prepare callback of bonding driver is not
implemented. Instead, the rte_eth_dev_tx_prepare() will be called for
all the fast path packet in mode 0, 1, 2, 4, 5, 6. In this way, all
tx_offloads can be processed correctly for all NIC devices in these modes.
If tx_prepare is not required in some cases, then slave PMDs tx_prepare
pointer should be NULL and rte_eth_tx_prepare() will be just a NOOP.
In these cases, the impact on performance will be very limited. It is
the responsibility of the slave PMDs to decide when the real tx_prepare
needs to be used. The information from dev_config/queue_setup is
sufficient for them to make these decisions.

Note:
The rte_eth_tx_prepare is not added to bond mode 3(Broadcast). This is
because in broadcast mode, a packet needs to be sent by all slave ports.
Different PMDs process the packets differently in tx_prepare. As a result,
the sent packet may be incorrect.

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
---
 drivers/net/bonding/rte_eth_bond.h     |  1 -
 drivers/net/bonding/rte_eth_bond_pmd.c | 28 ++++++++++++++++++++++++----
 2 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/drivers/net/bonding/rte_eth_bond.h b/drivers/net/bonding/rte_eth_bond.h
index 874aa91..1e6cc6d 100644
--- a/drivers/net/bonding/rte_eth_bond.h
+++ b/drivers/net/bonding/rte_eth_bond.h

@@ -343,7 +343,6 @@ rte_eth_bond_link_up_prop_delay_set(uint16_t bonded_port_id,
 int
 rte_eth_bond_link_up_prop_delay_get(uint16_t bonded_port_id);

-
 #ifdef __cplusplus
 }
 #endif

diff --git a/drivers/net/bonding/rte_eth_bond_pmd.c b/drivers/net/bonding/rte_eth_bond_pmd.c
index 2e9cea5..84af348 100644
--- a/drivers/net/bonding/rte_eth_bond_pmd.c
+++ b/drivers/net/bonding/rte_eth_bond_pmd.c

@@ -606,8 +606,14 @@ bond_ethdev_tx_burst_round_robin(void *queue, struct rte_mbuf **bufs,
 	/* Send packet burst on each slave device */
 	for (i = 0; i < num_of_slaves; i++) {
 		if (slave_nb_pkts[i] > 0) {
+			int nb_prep_pkts;
+
+			nb_prep_pkts = rte_eth_tx_prepare(slaves[i],
+					bd_tx_q->queue_id, slave_bufs[i],
+					slave_nb_pkts[i]);
+