netdev - Re: [PATCH net] net: dsa: tag_rtl4

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Date:   Mon, 30 Aug 2021 10:29:13 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        DENG Qingfang <dqfext@...il.com>,
        Mauri Sandberg <sandberg@...lfence.com>
Subject: Re: [PATCH net] net: dsa: tag_rtl4_a: Fix egress tags

On Sun, Aug 29, 2021 at 01:56:19AM +0200, Linus Walleij wrote:
> I noticed that only port 0 worked on the RTL8366RB since we
> started to use custom tags.
> 
> It turns out that the format of egress custom tags is actually
> different from ingress custom tags. While the lower bits just
> contain the port number in ingress tags, egress tags need to
> indicate destination port by setting the bit for the
> corresponding port.
> 
> It was working on port 0 because port 0 added 0x00 as port
> number in the lower bits, and if you do this the packet gets
> broadcasted to all ports, including the intended port.
> Ooops.

Does it get broadcast, or forwarded by MAC DA/VLAN ID as you'd expect
for a regular data packet?

> 
> Fix this and all ports work again.
> 
> Tested on the D-Link DIR-685 by sending traffic to each of
> the ports in turn. It works.
> 
> Fixes: 86dd9868b878 ("net: dsa: tag_rtl4_a: Support also egress tags")
> Cc: DENG Qingfang <dqfext@...il.com>
> Cc: Mauri Sandberg <sandberg@...lfence.com>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
>  net/dsa/tag_rtl4_a.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/net/dsa/tag_rtl4_a.c b/net/dsa/tag_rtl4_a.c
> index 57c46b4ab2b3..042a6cb7704a 100644
> --- a/net/dsa/tag_rtl4_a.c
> +++ b/net/dsa/tag_rtl4_a.c
> @@ -54,9 +54,10 @@ static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
>  	p = (__be16 *)tag;
>  	*p = htons(RTL4_A_ETHERTYPE);
>  
> -	out = (RTL4_A_PROTOCOL_RTL8366RB << 12) | (2 << 8);

What was 2 << 8? This patch changes that part.

> -	/* The lower bits is the port number */
> -	out |= (u8)dp->index;
> +	out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT);
> +	/* The lower bits indicate the port number */
> +	out |= BIT(dp->index);
> +
>  	p = (__be16 *)(tag + 2);
>  	*p = htons(out);
>  
> -- 
> 2.31.1
>