linux-kernel - Re: [PATCH net-next v2 7/7] net: dsa: vsc73xx: fix MTU configuration

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Date:   Wed, 28 Jun 2023 22:04:00 +0200
From:   Paweł Dembicki <paweldembicki@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     netdev@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 7/7] net: dsa: vsc73xx: fix MTU configuration

niedz., 25 cze 2023 o 16:54 Vladimir Oltean <olteanv@...il.com> napisał(a):
>
> On Sun, Jun 25, 2023 at 01:53:42PM +0200, Pawel Dembicki wrote:
> > Switch in MAXLEN register store maximum size of data frame.
> > MTU size is 18 bytes smaller than frame size.
> >
> > Current settings causes problems with packet forwarding.
> > This patch fix MTU settings to proper values.
> >
> > Fixes: fb77ffc6ec86 ("net: dsa: vsc73xx: make the MTU configurable")
> > Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> > Signed-off-by: Pawel Dembicki <paweldembicki@...il.com>
> > ---
>
> Please split this patch from the rest of the series and re-target it
> towards net.git.
>

I resend it.
https://lore.kernel.org/netdev/20230628194327.1765644-1-paweldembicki@gmail.com/

--
Pawel Dembicki

> > v2:
> >   - fix commit message style issue
> >
> >  drivers/net/dsa/vitesse-vsc73xx-core.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/dsa/vitesse-vsc73xx-core.c b/drivers/net/dsa/vitesse-vsc73xx-core.c
> > index c946464489ab..59bb3dbe780a 100644
> > --- a/drivers/net/dsa/vitesse-vsc73xx-core.c
> > +++ b/drivers/net/dsa/vitesse-vsc73xx-core.c
> > @@ -979,17 +979,18 @@ static int vsc73xx_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
> >       struct vsc73xx *vsc = ds->priv;
> >
> >       return vsc73xx_write(vsc, VSC73XX_BLOCK_MAC, port,
> > -                          VSC73XX_MAXLEN, new_mtu);
> > +                          VSC73XX_MAXLEN, new_mtu + ETH_HLEN + ETH_FCS_LEN);
> >  }
> >
> >  /* According to application not "VSC7398 Jumbo Frames" setting
> > - * up the MTU to 9.6 KB does not affect the performance on standard
> > + * up the frame size to 9.6 KB does not affect the performance on standard
> >   * frames. It is clear from the application note that
> >   * "9.6 kilobytes" == 9600 bytes.
> >   */
> >  static int vsc73xx_get_max_mtu(struct dsa_switch *ds, int port)
> >  {
> > -     return 9600;
> > +     /* max mtu = 9600 - ETH_HLEN - ETH_FCS_LEN */
> > +     return 9582;
>
> This can also be:
>
>         return 9600 - ETH_HLEN - ETH_FCS_LEN;
>
> since the arithmetic is on constants, it can be evaluated at compile
> time and it results in the same generated code, but the comment is no
> longer necessary.
>
> >  }
> >
> >  static void vsc73xx_port_stp_state_set(struct dsa_switch *ds, int port,
> > --
> > 2.34.1
> >
>