netdev - Re: [PATCH v3 net-next 5/7] net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag

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Date:   Sat, 16 Oct 2021 14:04:29 +0800
From:   DENG Qingfang <dqfext@...il.com>
To:     Alvin Šipraga <alvin@...s.dk>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net-next 5/7] net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag

On Fri, Oct 15, 2021 at 07:10:26PM +0200, Alvin Šipraga wrote:
> +static struct sk_buff *rtl8_4_tag_xmit(struct sk_buff *skb,
> +				       struct net_device *dev)
> +{
> +	struct dsa_port *dp = dsa_slave_to_port(dev);
> +	__be16 *tag;
> +
> +	/* Pad out so the (stripped) packet is at least 64 bytes long
> +	 * (including FCS), otherwise the switch will drop the packet.
> +	 * Then we need an additional 8 bytes for the Realtek tag.
> +	 */
> +	if (unlikely(__skb_put_padto(skb, ETH_ZLEN + RTL8_4_TAG_LEN, false)))
> +		return NULL;

Is this still required if you set rtl8365mb_cpu_rxlen to 64 bytes already?

> +
> +	skb_push(skb, RTL8_4_TAG_LEN);
> +