netdev - Re: [PATCH 1/2] net: emac: implement 802.1Q VLAN TX tagging support

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Date:   Wed, 17 Oct 2018 13:08:21 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Christian Lamparter <chunkeey@...il.com>, netdev@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH 1/2] net: emac: implement 802.1Q VLAN TX tagging support

On 10/17/2018 12:53 PM, Christian Lamparter wrote:
> As per' APM82181 Embedded Processor User Manual 26.1 EMAC Features:
> VLAN:
>  - Support for VLAN tag ID in compliance with IEEE 802.3ac.
>  - VLAN tag insertion or replacement for transmit packets
> 
> This patch completes the missing code for the VLAN tx tagging
> support, as the the EMAC_MR1_VLE was already enabled.
> 
> Signed-off-by: Christian Lamparter <chunkeey@...il.com>
> ---
>  drivers/net/ethernet/ibm/emac/core.c | 32 ++++++++++++++++++++++++----
>  drivers/net/ethernet/ibm/emac/core.h |  6 +++++-
>  2 files changed, 33 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
> index 760b2ad8e295..be560f9031f4 100644
> --- a/drivers/net/ethernet/ibm/emac/core.c
> +++ b/drivers/net/ethernet/ibm/emac/core.c
> @@ -37,6 +37,7 @@
>  #include <linux/ethtool.h>
>  #include <linux/mii.h>
>  #include <linux/bitops.h>
> +#include <linux/if_vlan.h>
>  #include <linux/workqueue.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> @@ -674,7 +675,7 @@ static int emac_configure(struct emac_instance *dev)
>  		 ndev->dev_addr[5]);
>  
>  	/* VLAN Tag Protocol ID */
> -	out_be32(&p->vtpid, 0x8100);
> +	out_be32(&p->vtpid, ETH_P_8021Q);
>  
>  	/* Receive mode register */
>  	r = emac_iff2rmr(ndev);
> @@ -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));

The only case where this is likely not going to be 0x8100/ETH_P_8021Q is
if you do 802.1ad (QinQ) and you decided to somehow offload the S-Tag
instead of the C-Tag.

It would be a shame to slow down your TX path with an expensive register
write, when maybe inserting the VLAN in software amounts to the same
performance result ;)
-- 
Florian