netdev - Re: [PATCH net 1/4] net:ethernet:aquantia: Setup max

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Date:   Fri, 22 Sep 2017 10:24:30 +0300
From:   Igor Russkikh <igor.russkikh@...antia.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        David Arcari <darcari@...hat.com>,
        Pavel Belous <Pavel.Belous@...antia.com>,
        Nadezhda Krupnina <Nadezhda.Krupnina@...antia.com>,
        Simon Edelhaus <simon.edelhaus@...antia.com>
Subject: Re: [PATCH net 1/4] net:ethernet:aquantia: Setup max_mtu in ndev to
 enable jumbo frames


>>  	self->ndev->mtu = aq_nic_cfg->mtu - ETH_HLEN;
>> +	self->ndev->min_mtu = ETH_MIN_MTU;
> This is not required. It will default to ETH_MIN_MTU.

Thanks Andrew, true.

>> +	self->ndev->max_mtu = self->aq_hw_caps.mtu - ETH_FCS_LEN - ETH_HLEN;
>>  
>>  	return 0;
>>  }
>> @@ -695,7 +696,7 @@ int aq_nic_set_mtu(struct aq_nic_s *self, int new_mtu)
>>  {
>>  	int err = 0;
>>  
>> -	if (new_mtu > self->aq_hw_caps.mtu) {
>> +	if (new_mtu + ETH_FCS_LEN > self->aq_hw_caps.mtu) {
> If you have set max_mtu correctly, this cannot happen.  But it seems
> odd you don't have ETH_HLEN here, where as when setting max_mtu you
> do.

I agree, thats an extra check. Will remove that.
Regarding ETH_HLEN - the baseline code invokes this function with (new_mtu + ETH_HLEN)  - thats why this check does not add it. In general, that extra level of storage (aq_nic_cfg.mtu field) is almost useless, I'll cleanup this under a separate patchset.

-- 
BR,
  Igor