linux-kernel - Re: [PATCH v3] net: stmmac: fix maxmtu assignment to be within valid range

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Message-ID: <CAHp75VeWs8LXS+zaCht8reLMLRtz+583K91QvoPquuUxC-rwWg@mail.gmail.com>
Date:   Sat, 7 Jan 2017 02:07:14 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     "Kweh, Hock Leong" <hock.leong.kweh@...el.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Giuseppe CAVALLARO <peppe.cavallaro@...com>,
        "seraphin.bonnaffe@...com" <seraphin.bonnaffe@...com>,
        Jarod Wilson <jarod@...hat.com>,
        Alexandre TORGUE <alexandre.torgue@...il.com>,
        Joachim Eastwood <manabian@...il.com>,
        Niklas Cassel <niklas.cassel@...s.com>,
        Johan Hovold <johan@...nel.org>, Pavel Machek <pavel@....cz>,
        "lars.persson@...s.com" <lars.persson@...s.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] net: stmmac: fix maxmtu assignment to be within valid range

On Sat, Jan 7, 2017 at 1:47 AM, Kweh, Hock Leong
<hock.leong.kweh@...el.com> wrote:

>> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> > @@ -3345,8 +3345,14 @@ int stmmac_dvr_probe(struct device *device,
>> >                 ndev->max_mtu = JUMBO_LEN;
>> >         else
>> >                 ndev->max_mtu = SKB_MAX_HEAD(NET_SKB_PAD + NET_IP_ALIGN);
>> > -       if (priv->plat->maxmtu < ndev->max_mtu)
>>
>> > +       if ((priv->plat->maxmtu < ndev->max_mtu) &&
>> > +           (priv->plat->maxmtu >= ndev->min_mtu))
>>
>> >                 ndev->max_mtu = priv->plat->maxmtu;
>>
>> > +       else if (priv->plat->maxmtu < ndev->min_mtu)
>>
>> And if it > ndev->max_mtu?..
>>
>
> Base on my understanding to the original code, the "maxmtu >= ndev->max_mtu"
> is meant for products that would want to use the value from logic which is just above
> this statement where you just ask me not to add new line. That the reason the
> stmmac_platform.c put in "plat->maxmtu = JUMBO_LEN;" as generic and I also
> follow it in stmmac_pci.c.
>
> Or do you mean only take maxmtu = JUMBO_LEN for the option to use driver itself
> assignment statement above and all the > max_mtu consider invalid?

So, just answer to the simple question: is it a valid case to have
plat->maxmtu > ndev->max_mtu? If it so, how is it used?
Otherwise we need a warning in such case. What did I miss?

>
>> > +               netdev_warn(priv->dev,
>> > +                           "%s: warning: maxmtu having invalid value (%d)\n",
>> > +                           __func__, priv->plat->maxmtu);


>> > +       /* Set the maxmtu to a default of JUMBO_LEN in case the
>> > +        * parameter is not defined for the device.
>> > +        */
>> > +       plat->maxmtu = JUMBO_LEN;
>>
>> Please, use *_default_data() hooks for that.
>>
>> At some point it might make sense to extract
>> static int common_default_data() {...}
>> and call it at the beginning of the rest of *_defautl_data() hooks.
>>
>
> Just try to understand, are you referring changing the code something
> like this:
>
>         stmmac_default_data(plat);
>         if (info) {
>                 info->pdev = pdev;
>                 if (info->setup) {
>                         ret = info->setup(plat, info);
>                         if (ret)
>                                 return ret;
>                 }
>         }
>
> Where all the common code is inside the stmmac_default_data()?

No.

common_default_data()
{
 ... common defaults among *_default_data() ...
}

*_default_data()
{
...
 common_default_data();
 ...
}

-- 
With Best Regards,
Andy Shevchenko