netdev - Re: [PATCH net 2/6] net: dsa: ksz: move tag/untag action

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Date:   Wed, 13 Jan 2021 15:35:07 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Gilles DOFFE <gilles.doffe@...oirfairelinux.com>,
        netdev@...r.kernel.org
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 2/6] net: dsa: ksz: move tag/untag action

On 1/13/21 4:45 AM, Gilles DOFFE wrote:
> Move tag/untag action at the end of the function to avoid
> tagging or untagging traffic if only vlan 0 is handled.
> 
> Signed-off-by: Gilles DOFFE <gilles.doffe@...oirfairelinux.com>
> ---
>  drivers/net/dsa/microchip/ksz8795.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/dsa/microchip/ksz8795.c b/drivers/net/dsa/microchip/ksz8795.c
> index 6962ba4ee125..4b060503b2e8 100644
> --- a/drivers/net/dsa/microchip/ksz8795.c
> +++ b/drivers/net/dsa/microchip/ksz8795.c
> @@ -840,8 +840,6 @@ static void ksz8795_port_vlan_add(struct dsa_switch *ds, int port,
>  	u8 fid, member, valid;
>  	int ret;
>  
> -	ksz_port_cfg(dev, port, P_TAG_CTRL, PORT_REMOVE_TAG, untagged);
> -
>  	for (vid = vlan->vid_begin; vid <= vlan->vid_end; vid++) {
>  		if (vid == 0)
>  			continue;
> @@ -874,6 +872,8 @@ static void ksz8795_port_vlan_add(struct dsa_switch *ds, int port,
>  		vid |= new_pvid;
>  		ksz_pwrite16(dev, port, REG_PORT_CTRL_VID, vid);
>  	}
> +
> +	ksz_port_cfg(dev, port, P_TAG_CTRL, PORT_REMOVE_TAG, untagged);

You should be giving an example how this fails, because it is not
immediately obvious why this fixes a problem and how it does fix it,
especially for VID == 0 given that the loop would be skipped over.
--
Florian