linux-kernel - Re: [PATCH net-next] mvpp2: document HW checksum behaviour

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Date:   Fri, 26 Jul 2019 16:35:59 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] mvpp2: document HW checksum behaviour

On Fri, Jul 26, 2019 at 2:57 PM Antoine Tenart
<antoine.tenart@...tlin.com> wrote:
>
> Hi Matteo,
>
> On Fri, Jul 26, 2019 at 01:15:46AM +0200, Matteo Croce wrote:
> > The hardware can only offload checksum calculation on first port due to
> > the Tx FIFO size limitation. Document this in a comment.
> >
> > Fixes: 576193f2d579 ("net: mvpp2: jumbo frames support")
> > Signed-off-by: Matteo Croce <mcroce@...hat.com>
>
> Looks good. Please note there's a similar code path in the probe. You
> could also add a comment there (or move this check/comment in a common
> place).
>
> Thanks!
> Antoine
>
> > ---
> >  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> > index d8e5241097a9..2f7286bd203b 100644
> > --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> > +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> > @@ -843,7 +843,10 @@ static int mvpp2_bm_update_mtu(struct net_device *dev, int mtu)
> >               /* Add port to new short & long pool */
> >               mvpp2_swf_bm_pool_init(port);
> >
> > -             /* Update L4 checksum when jumbo enable/disable on port */
> > +             /* Update L4 checksum when jumbo enable/disable on port.
> > +              * Only port 0 supports hardware checksum offload due to
> > +              * the Tx FIFO size limitation.
> > +              */
> >               if (new_long_pool == MVPP2_BM_JUMBO && port->id != 0) {
> >                       dev->features &= ~(NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM);
> >                       dev->hw_features &= ~(NETIF_F_IP_CSUM |
> > --
> > 2.21.0
> >
>
> --
> Antoine Ténart, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

I see, there is a similar statement in mvpp2_port_probe().
What about adding a static function which sets the flag, and add the
comment there instead of duplicating the comment?

-- 
Matteo Croce
per aspera ad upstream