netdev - Re: [PATCH] net: dsa: ksz: Increase the tag alignment

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Date:   Mon, 10 Dec 2018 22:56:32 +0100
From:   Marek Vasut <marex@...x.de>
To:     Tristram.Ha@...rochip.com
Cc:     vivien.didelot@...oirfairelinux.com, andrew@...n.ch,
        Woojung.Huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        davem@...emloft.net, netdev@...r.kernel.org, f.fainelli@...il.com
Subject: Re: [PATCH] net: dsa: ksz: Increase the tag alignment

On 12/10/2018 10:49 PM, Tristram.Ha@...rochip.com wrote:
>> I am not looking for a hack-around, I am looking for a proper solution.
>>
> 
> As you have the hardware you can try something to correct the problem.
> 
> The change was introduced in commit 9421c9015047 on Nov 15.  In the
> net-next tree it is about -42 commits.
> 
> git log -42 cpsw.c
> 
> git diff f5b589488ea5 cpsw.c shows the changes.
> 
> As explained in the commit log this corrects the problem of sending a
> tagged frame and the VLAN tag is removed by the hardware.
> 
> I do not think the implementation is 100% correct but maybe it is too
> much to check for VLAN tag every time a frame is sent.  The change assumes
> a VLAN tag is always there and it may be dropped.
> 
> The MAC controller uses VLAN for its dual MAC function, but it is added
> automatically and not done at system level.  If the VLAN tag is removed all
> the time it is pointless to put it in the first place by software.  The connected
> switch also has some functions to manipulate the VLAN tag.
> 
> Are you actively using the second Ethernet device which is not connected to
> the switch and is using VLAN?

Yes, I'm using it in dual-ethernet configuration, so I am using both
ethernets.

> There should be a way to use device tree to specify which function to enable.
> 


-- 
Best regards,
Marek Vasut