netdev - Re: [PATCH v3 1/3] dsa: marvell: Provide per device information about max frame size

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Message-ID: <20230105184419.7b409a2d@wsk>
Date:   Thu, 5 Jan 2023 18:44:19 +0100
From:   Lukasz Majewski <lukma@...x.de>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, Vladimir Oltean <olteanv@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dsa: marvell: Provide per device information
 about max frame size

Hi Alexander

> On Thu, Jan 5, 2023 at 2:37 AM Lukasz Majewski <lukma@...x.de> wrote:
> >
> > Hi Andrew, Alexander,
> >  
> > > Hi Andrew,
> > >  
> > > > > @@ -3548,7 +3548,9 @@ static int mv88e6xxx_get_max_mtu(struct
> > > > > dsa_switch *ds, int port) if
> > > > > (chip->info->ops->port_set_jumbo_size) return 10240 -
> > > > > VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN; else if
> > > > > (chip->info->ops->set_max_frame_size)
> > > > > -         return 1632 - VLAN_ETH_HLEN - EDSA_HLEN -
> > > > > ETH_FCS_LEN;
> > > > > +         return (max_t(int, chip->info->max_frame_size,
> > > > > 1632)
> > > > > +                 - VLAN_ETH_HLEN - EDSA_HLEN -
> > > > > ETH_FCS_LEN); +
> > > > >   return 1522 - VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;
> > > > >  
> > > >
> > > > I would also prefer if all this if/else logic is removed, and
> > > > the code simply returned chip->info->max_frame_size -
> > > > VLAN_ETH_HLEN - EDSA_HLEN - ETH_FCS_LEN;
> > > >  
> > >
> > > So then the mv88e6xxx_get_max_mtu shall look like:
> > >
> > > WARN_ON_ONCE(!chip->info->max_frame_size)
> > >
> > > if (chip->info->ops->port_set_jumbo_size)
> > > ...
> > > else
> > >     return chip->info->max_frame_size - VLAN_ETH_HLEN -
> > >       EDSA_HLEN - ETH_FCS_LEN;
> > >
> > >
> > > Or shall I put WARN_ON_ONCE to the mv88e6xxx_probe() function?
> > >
> > >
> > > The above approach is contrary to one proposed by Alexander, who
> > > wanted to improve the defensive approach in this driver (to avoid
> > > situation where the max_frame_size callback is not defined and
> > > max_frame_size member of *_info struct is not added by developer).
> > >
> > > Which approach is the recommended one for this driver?  
> >
> > Is there any decision regarding the preferred approach to rewrite
> > this code?  
> 
> I would defer to what Andrew proposed since he has more experience
> with the DSA code than I do.
> 

Ok, then I will prepare v4 according to Andrew suggestions.

Thanks for the update :-)

> Thanks,
> 
> - Alex




Best regards,

Lukasz Majewski

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