netdev - Re: [PATCH v4 1/3] net: emac: implement 802.1Q VLAN TX tagging support

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Message-Id: <20181106.150954.2230387672447683694.davem@davemloft.net>
Date:   Tue, 06 Nov 2018 15:09:54 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     chunkeey@...il.com
Cc:     netdev@...r.kernel.org, ivan@...ibm.com, f.fainelli@...il.com
Subject: Re: [PATCH v4 1/3] net: emac: implement 802.1Q VLAN TX tagging
 support

From: Christian Lamparter <chunkeey@...il.com>
Date: Tue,  6 Nov 2018 23:27:49 +0100

> @@ -1435,6 +1436,22 @@ static inline netdev_tx_t emac_xmit_finish(struct emac_instance *dev, int len)
>  	return NETDEV_TX_OK;
>  }
>  
> +static inline u16 emac_tx_vlan(struct emac_instance *dev, struct sk_buff *skb)
> +{
> +	/* Handle VLAN TPID and TCI insert if this is a VLAN skb */
> +	if (emac_has_feature(dev, EMAC_FTR_HAS_VLAN_CTAG_TX) &&
> +	    skb_vlan_tag_present(skb)) {
> +		struct emac_regs __iomem *p = dev->emacp;
> +
> +		/* update the VLAN TCI */
> +		out_be32(&p->vtci, (u32)skb_vlan_tag_get(skb));

Hmmm, how does this vtci register work?

How can you have a global piece of register state controlling the VLAN
tag that will be used for the TX frame?

What happens if you queue up several TX SKBs, each one with a different
VLAN tci?

Normally the TCI state is implemented on a per-tx-descriptor basis.