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Date:   Wed, 21 Jul 2021 20:56:56 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        andrew@...n.ch, vivien.didelot@...il.com, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] net: dsa: ensure linearized SKBs in case of tail
 taggers



On 7/21/2021 4:35 PM, Vladimir Oltean wrote:
> On Wed, Jul 21, 2021 at 11:56:41PM +0200, Lino Sanfilippo wrote:
>> The function skb_put() that is used by tail taggers to make room for the
>> DSA tag must only be called for linearized SKBS. However in case that the
>> slave device inherited features like NETIF_F_HW_SG or NETIF_F_FRAGLIST the
>> SKB passed to the slaves transmit function may not be linearized.
>> Avoid those SKBs by clearing the NETIF_F_HW_SG and NETIF_F_FRAGLIST flags
>> for tail taggers.
>> Furthermore since the tagging protocol can be changed at runtime move the
>> code for setting up the slaves features into dsa_slave_setup_tagger().
>>
>> Suggested-by: Vladimir Oltean <olteanv@...il.com>
>> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
>> ---
>>   net/dsa/slave.c | 14 +++++++++-----
>>   1 file changed, 9 insertions(+), 5 deletions(-)
>>
>> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
>> index 22ce11cd770e..ae2a648ed9be 100644
>> --- a/net/dsa/slave.c
>> +++ b/net/dsa/slave.c
>> @@ -1808,6 +1808,7 @@ void dsa_slave_setup_tagger(struct net_device *slave)
>>   	struct dsa_slave_priv *p = netdev_priv(slave);
>>   	const struct dsa_port *cpu_dp = dp->cpu_dp;
>>   	struct net_device *master = cpu_dp->master;
>> +	const struct dsa_switch *ds = dp->ds;
>>   
>>   	slave->needed_headroom = cpu_dp->tag_ops->needed_headroom;
>>   	slave->needed_tailroom = cpu_dp->tag_ops->needed_tailroom;
>> @@ -1819,6 +1820,14 @@ void dsa_slave_setup_tagger(struct net_device *slave)
>>   	slave->needed_tailroom += master->needed_tailroom;
>>   
>>   	p->xmit = cpu_dp->tag_ops->xmit;
>> +
>> +	slave->features = master->vlan_features | NETIF_F_HW_TC;
>> +	if (ds->ops->port_vlan_add && ds->ops->port_vlan_del)
>> +		slave->features |= NETIF_F_HW_VLAN_CTAG_FILTER;
>> +	slave->hw_features |= NETIF_F_HW_TC;
>> +	slave->features |= NETIF_F_LLTX;
>> +	if (slave->needed_tailroom)
>> +		slave->features &= ~(NETIF_F_SG | NETIF_F_FRAGLIST);
>>   }
>>   
>>   static struct lock_class_key dsa_slave_netdev_xmit_lock_key;
>> @@ -1881,11 +1890,6 @@ int dsa_slave_create(struct dsa_port *port)
>>   	if (slave_dev == NULL)
>>   		return -ENOMEM;
>>   
>> -	slave_dev->features = master->vlan_features | NETIF_F_HW_TC;
>> -	if (ds->ops->port_vlan_add && ds->ops->port_vlan_del)
>> -		slave_dev->features |= NETIF_F_HW_VLAN_CTAG_FILTER;
>> -	slave_dev->hw_features |= NETIF_F_HW_TC;
>> -	slave_dev->features |= NETIF_F_LLTX;
>>   	slave_dev->ethtool_ops = &dsa_slave_ethtool_ops;
>>   	if (!is_zero_ether_addr(port->mac))
>>   		ether_addr_copy(slave_dev->dev_addr, port->mac);
>> -- 
>> 2.32.0
>>
> 
> I would have probably changed the code in dsa_slave_create just like
> this:
> 
> -	slave->features = master->vlan_features | NETIF_F_HW_TC;
> +	slave->features = NETIF_F_HW_TC;
> ...
> -	slave_dev->vlan_features = master->vlan_features;
> 
> and in dsa_slave_setup_tagger:
> 
> +	vlan_features = master->vlan_features;
> +	slave->features &= ~vlan_features;
> +	if (slave->needed_tailroom)
> +		vlan_features &= ~(NETIF_F_SG | NETIF_F_FRAGLIST);
> +	slave->features |= vlan_features;
> +	slave->vlan_features = vlan_features;
> 
> no need to move around NETIF_F_HW_TC and NETIF_F_LLTX. Makes sense?
> 
> And I would probably add:
> 
> Fixes: 91da11f870f0 ("net: Distributed Switch Architecture protocol support")

Agreed, with those fixed:

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian

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