Re: [PATCH net-next 1/2] net: enetc: declare NETIF_F_IP_CSUM and do it in software

[Ioana Ciornei <ioana.ciornei@nxp.com>]

On Wed, Oct 06, 2021 at 05:24:18PM -0700, Jakub Kicinski wrote:
> On Wed,  6 Oct 2021 23:13:07 +0300 Ioana Ciornei wrote:
> > This is just a preparation patch for software TSO in the enetc driver.
> > Unfortunately, ENETC does not support Tx checksum offload which would
> > normally render TSO, even software, impossible.
> > 
> > Declare NETIF_F_IP_CSUM as part of the feature set and do it at driver
> > level using skb_csum_hwoffload_help() so that we can move forward and
> > also add support for TSO in the next patch.
> > 
> > Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
> 
> Did you choose NETIF_F_IP_CSUM intentionally?
> It'll only support IPv4, and since you always fall back to SW
> I'd think NETIF_F_HW_CSUM makes more sense.

Somewhat intentionally, yes.

If I would use NETIF_F_HW_CSUM, as I understand it, the GSO path, added
in the next patch, would have to compute the checksum not only for IPv6
but also for any other protocols other than UDP and TCP (which currently
it supports).
I just didn't look into that at the moment.

> 
> > diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
> > index 3cbfa8b4e265..a92bfd660f22 100644
> > --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> > +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> > @@ -319,7 +319,7 @@ static netdev_tx_t enetc_start_xmit(struct sk_buff *skb,
> >  {
> >  	struct enetc_ndev_priv *priv = netdev_priv(ndev);
> >  	struct enetc_bdr *tx_ring;
> > -	int count;
> > +	int count, err;
> >  
> >  	/* Queue one-step Sync packet if already locked */
> >  	if (skb->cb[0] & ENETC_F_TX_ONESTEP_SYNC_TSTAMP) {
> > @@ -342,6 +342,12 @@ static netdev_tx_t enetc_start_xmit(struct sk_buff *skb,
> >  		return NETDEV_TX_BUSY;
> >  	}
> >  
> > +	if (skb->ip_summed == CHECKSUM_PARTIAL) {
> > +		err = skb_csum_hwoffload_help(skb, 0);
> > +		if (err)
> > +			goto drop_packet_err;
> > +	}
> 
> Any reason no to call skb_checksum_help() directly?

No, no reason. Will change.

Ioana