netdev - Re: [PATCH net-next] net: dsa: mt7530: enable jumbo frame

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Message-ID: <c7da2de5-5e25-6284-0b35-fd2dbceb9c4f@gmail.com>
Date:   Thu, 9 Apr 2020 19:27:06 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     DENG Qingfang <dqfext@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org,
        René van Dorst <opensource@...rst.com>,
        John Crispin <john@...ozen.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Sean Wang <sean.wang@...iatek.com>,
        Weijie Gao <weijie.gao@...iatek.com>,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next] net: dsa: mt7530: enable jumbo frame



On 4/9/2020 7:19 PM, DENG Qingfang wrote:
> So, since nothing else uses the mt7530_set_jumbo function, should I
> remove the function and just add a single rmw to mt7530_setup?

(please do not top-post on netdev)

There is a proper way to support the MTU configuration for DSA switch
drivers which is:

        /*
         * MTU change functionality. Switches can also adjust their MRU
through
         * this method. By MTU, one understands the SDU (L2 payload) length.
         * If the switch needs to account for the DSA tag on the CPU
port, this
         * method needs to to do so privately.
         */
        int     (*port_change_mtu)(struct dsa_switch *ds, int port,
                                   int new_mtu);
        int     (*port_max_mtu)(struct dsa_switch *ds, int port);

> 
> On Fri, Apr 10, 2020 at 1:20 AM David Miller <davem@...emloft.net> wrote:
>>
>> From: DENG Qingfang <dqfext@...il.com>
>> Date: Thu,  9 Apr 2020 23:54:09 +0800
>>
>>> +static void
>>> +mt7530_set_jumbo(struct mt7530_priv *priv, u8 kilobytes)
>>> +{
>>> +     if (kilobytes > 15)
>>> +             kilobytes = 15;
>>  ...
>>> +     /* Enable jumbo frame up to 15 KB */
>>> +     mt7530_set_jumbo(priv, 15);
>>
>> You've made the test quite pointless, honestly.

-- 
Florian