Subject: Re: [PATCH net-next v2 02/12] net: dsa: add Broadcom tag hook

From: Florian Fainelli <[email-masked]>
Date: Wed, 06 Aug 2014 11:37:59 -0700

On 08/06/2014 07:47 AM, Alexander Duyck wrote:
> On 08/05/2014 03:31 PM, Florian Fainelli wrote:
>> Register a fake Ethertype for the Broadcom tag to allow us to hook into
>> a given Ethernet device receive path and parse this Broadcom tag.
>>
>> Signed-off-by: Florian Fainelli <[email-masked]>

[snip]

>> diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
>> index f405e0592407..6b67653d5283 100644
>> --- a/net/ethernet/eth.c
>> +++ b/net/ethernet/eth.c
>> @@ -186,6 +186,8 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
>>  
>>  	if (unlikely(netdev_uses_trailer_tags(dev)))
>>  		return htons(ETH_P_TRAILER);
>> +	if (netdev_uses_brcm_tags(dev))
>> +		return htons(ETH_P_BRCMTAG);
>>  
>>  	if (likely(ntohs(eth->h_proto) >= ETH_P_802_3_MIN))
>>  		return eth->h_proto;
>>
> 
> Maybe we should consider some change to this logic.  Maybe a bit flag in
> the dsa_switch_tree structure that indicates if eth_type_trans should
> override the protocol or not.

I just tested something like this, which becomes protocol agnostic:

if (unlikely(netdev_uses_dsa(dev)))
	return dsa_tag_protocol(dev);

include/linux/netdevice.h:
static inline bool netdev_uses_dsa(struct net_device *dev)
{
#ifdef CONFIG_NET_DSA
	return dev->dsa_ptr != NULL;
#else
	return false;
#endif
}

include/net/dsa.h:
static __be16 netdev_dsa_protocol(struct net_device *dev)
{
#ifdef CONFIG_NET_DSA
	struct dsa_switch_tree *dst = dev->dsa_ptr;
	return dst->tag_protocol;
#endif
}

> Otherwise this is going to start becoming
> a rather large conditional statement if we have to add a new if every
> time a new switch is added.

Agreed.

> Thanks,
> Alex