Re: [dpdk-dev] [PATCH v12 0/6] add Tx preparation

[Thomas Monjalon <thomas.monjalon@6wind.com>]

We need attention of every PMD developers on this thread.

Reminder of what Konstantin suggested:
"
- if the PMD supports TX offloads AND
- if to be able use any of these offloads the upper layer SW would have to:
    * modify the contents of the packet OR
    * obey HW specific restrictions
then it is a PMD developer responsibility to provide tx_prep() that would implement
expected modifications of the packet contents and restriction checks.
Otherwise, tx_prep() implementation is not required and can be safely set to NULL.      
"

I copy/paste also my previous conclusion:

Before txprep, there is only one API: the application must prepare the
packets checksum itself (get_psd_sum in testpmd).
With txprep, the application have 2 choices: keep doing the job itself
or call txprep which calls a PMD-specific function.
The question is: does non-Intel drivers need a checksum preparation for TSO?
Will it behave well if txprep does nothing in these drivers?

When looking at the code, most of drivers handle the TSO flags.
But it is hard to know whether they rely on the pseudo checksum or not.

git grep -l 'PKT_TX_UDP_CKSUM\|PKT_TX_TCP_CKSUM\|PKT_TX_TCP_SEG' drivers/net/

drivers/net/bnxt/bnxt_txr.c
drivers/net/cxgbe/sge.c
drivers/net/e1000/em_rxtx.c
drivers/net/e1000/igb_rxtx.c
drivers/net/ena/ena_ethdev.c
drivers/net/enic/enic_rxtx.c
drivers/net/fm10k/fm10k_rxtx.c
drivers/net/i40e/i40e_rxtx.c
drivers/net/ixgbe/ixgbe_rxtx.c
drivers/net/mlx4/mlx4.c
drivers/net/mlx5/mlx5_rxtx.c
drivers/net/nfp/nfp_net.c
drivers/net/qede/qede_rxtx.c
drivers/net/thunderx/nicvf_rxtx.c
drivers/net/virtio/virtio_rxtx.c
drivers/net/vmxnet3/vmxnet3_rxtx.c

Please, we need a comment for each driver saying
"it is OK, we do not need any checksum preparation for TSO"
or
"yes we have to implement tx_prepare or TSO will not work in this mode"