linux-kernel - Re: [PATCH net-next 2/3] net: dsa: mediatek: combine MediaTek tag with VLAN tag

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Message-ID: <20171212082837.GM28672@lunn.ch>
Date:   Tue, 12 Dec 2017 09:28:37 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Sean Wang <sean.wang@...iatek.com>
Cc:     davem@...emloft.net, f.fainelli@...il.com,
        vivien.didelot@...oirfairelinux.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next 2/3] net: dsa: mediatek: combine MediaTek tag
 with VLAN tag

On Tue, Dec 12, 2017 at 03:21:21PM +0800, Sean Wang wrote:
> On Thu, 2017-12-07 at 16:30 +0100, Andrew Lunn wrote:
> > > @@ -25,20 +28,37 @@ static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
> > >  {
> > >  	struct dsa_port *dp = dsa_slave_to_port(dev);
> > >  	u8 *mtk_tag;
> > > +	bool is_vlan_skb = true;
> > 
> > ..
> > 
> > > +	/* Mark tag attribute on special tag insertion to notify hardware
> > > +	 * whether that's a combined special tag with 802.1Q header.
> > > +	 */
> > > +	mtk_tag[0] = is_vlan_skb ? MTK_HDR_XMIT_TAGGED_TPID_8100 :
> > > +		     MTK_HDR_XMIT_UNTAGGED;
> > >  	mtk_tag[1] = (1 << dp->index) & MTK_HDR_XMIT_DP_BIT_MASK;
> > > -	mtk_tag[2] = 0;
> > > -	mtk_tag[3] = 0;
> > > +
> > > +	/* Tag control information is kept for 802.1Q */
> > > +	if (!is_vlan_skb) {
> > > +		mtk_tag[2] = 0;
> > > +		mtk_tag[3] = 0;
> > > +	}
> > >  
> > >  	return skb;
> > >  }
> > 
> > Hi Sean
> > 
> > So you can mark a packet for egress. What about ingress? How do you
> > know the VLAN/PORT combination for packets the CPU receives? I would
> > of expected a similar change to mtk_tag_rcv().
> > 
> >    Andrew
> 
> Hi, Andrew
> 
> It's unnecessary for extra handling in mtk_tag_rcv() when VLAN tag is
> present since it is able to put the VLAN tag after the special tag and
> then follow the existing way to parse.

Hi Sean

O.K. Please mention this in the commit message. Since it was something
i was expecting, it should be documented why it is not needed.

  Thanks
	Andrew