netdev - Re: [PATCH v3 4/5] net: dsa: add support for Atheros AR9331 TAG format

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Date:   Mon, 21 Oct 2019 20:36:25 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Chris Snook <chris.snook@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        James Hogan <jhogan@...nel.org>,
        Jay Cliburn <jcliburn@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Paul Burton <paul.burton@...s.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Rob Herring <robh+dt@...nel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-mips@...r.kernel.org, Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v3 4/5] net: dsa: add support for Atheros AR9331 TAG
 format

On Mon, Oct 21, 2019 at 05:49:00PM +0200, Andrew Lunn wrote:
> > +static struct sk_buff *ar9331_tag_rcv(struct sk_buff *skb,
> > +				      struct net_device *ndev,
> > +				      struct packet_type *pt)
> > +{
> > +	u8 ver, port;
> > +	u16 hdr;
> > +
> > +	if (unlikely(!pskb_may_pull(skb, AR9331_HDR_LEN)))
> > +		return NULL;
> > +
> > +	hdr = le16_to_cpu(*(__le16 *)skb_mac_header(skb));
> > +
> > +	ver = FIELD_GET(AR9331_HDR_VERSION_MASK, hdr);
> > +	if (unlikely(ver != AR9331_HDR_VERSION)) {
> > +		netdev_warn_once(ndev, "%s:%i wrong header version 0x%2x\n",
> > +				 __func__, __LINE__, hdr);
> > +		return NULL;
> > +	}
> > +
> > +	if (unlikely(hdr & AR9331_HDR_FROM_CPU)) {
> > +		netdev_warn_once(ndev, "%s:%i packet should not be from cpu 0x%2x\n",
> > +				 __func__, __LINE__, hdr);
> > +		return NULL;
> > +	}
> > +
> > +	skb_pull(skb, AR9331_HDR_LEN);
> > +	skb_set_mac_header(skb, -ETH_HLEN);
> 
> No other tag driver calls skb_set_mac_header().  Also, the -ETH_HLEN
> looks odd, give you have just pulled off AR9331_HDR_LEN?

Hm.. is it corrected somewhere else? Any way, B.T.M.A.N need a proper
value ant it seems to work correctly. So I remove it.

> What other tag drivers use is skb_pull_rcsum().

It is build in switch and internal Ethernet controller do not set csum. There is
nothing to recalculate... on other hand, it adds no overhead. So, I have
nothing against it. Are there other arguments?

Regards,
Oleksij
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