Re: [PATCH] net: macb: Disable macb pad and fcs for fragmented packets

[Harini Katakam]

Hi Paolo,

On Tue, May 10, 2022 at 6:48 PM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>
> On Mon, 2022-05-09 at 17:45 +0530, Harini Katakam wrote:
> > data_len in skbuff represents bytes resident in fragment lists or
> > unmapped page buffers. For such packets, when data_len is non-zero,
> > skb_put cannot be used - this will throw a kernel bug. Hence do not
> > use macb_pad_and_fcs for such fragments.
> >
> > Signed-off-by: Harini Katakam <harini.katakam@xxxxxxxxxx>
> > Signed-off-by: Michal Simek <michal.simek@xxxxxxxxxx>
> > Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxxxxx>
>
> This looks like a fix suitable for the net tree. Please add a relevant
> 'Fixes' tag.
>
> > ---
> >  drivers/net/ethernet/cadence/macb_main.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> > index 6434e74c04f1..0b03305ad6a0 100644
> > --- a/drivers/net/ethernet/cadence/macb_main.c
> > +++ b/drivers/net/ethernet/cadence/macb_main.c
> > @@ -1995,7 +1995,8 @@ static unsigned int macb_tx_map(struct macb *bp,
> >                       ctrl |= MACB_BF(TX_LSO, lso_ctrl);
> >                       ctrl |= MACB_BF(TX_TCP_SEQ_SRC, seq_ctrl);
> >                       if ((bp->dev->features & NETIF_F_HW_CSUM) &&
> > -                         skb->ip_summed != CHECKSUM_PARTIAL && !lso_ctrl)
> > +                         skb->ip_summed != CHECKSUM_PARTIAL && !lso_ctrl &&
> > +                         (skb->data_len == 0))
> >                               ctrl |= MACB_BIT(TX_NOCRC);
> >               } else
> >                       /* Only set MSS/MFS on payload descriptors
>
> This chunk looks unrelated to the commit message ?!? only the next one
> looks relevant.

Thanks for the review. This code is related to the commit message.
macb_pad_and_fcs is performed on the same packets on which
TX_NOCRC is set (instruct HW not to perform CRC and perform
CRC in SW). This is the patch which added both:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/drivers/net/ethernet/cadence?id=653e92a9175ea7ed67efe209c725222051a3713d
I'll mention the same in Fixes tag and also add Claudiu's review tag.

Regards,
Harini