netdev - Re: [RFC net-next 2/2] net: dsa: mt7530: trap packets from standalone ports to the CPU

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Date:   Thu, 29 Jul 2021 19:50:27 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        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>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next 2/2] net: dsa: mt7530: trap packets from
 standalone ports to the CPU

On Fri, Jul 30, 2021 at 12:11:45AM +0800, DENG Qingfang wrote:
> On Thu, Jul 29, 2021 at 11:28 PM Vladimir Oltean <olteanv@...il.com> wrote:
> > Actually, on second thought...
> > If MT7530 supports 8 FIDs and it has 7 ports, then you can assign one
> > FID to each standalone port or VLAN-unaware bridge it is a member of.
> 
> The problem is, there is no way to do that..
> 
> According to the reference manual:
> Filter ID is learned automatically from VLAN Table. 0 is the default value if
> VLAN Table is not applicable.
> 
> So it is always 0 in VLAN-unaware mode.

I have the MT7621 GSW, and sadly this reference manual isn't the best in
explaining what is and what is not possible. For example, I am still not
clear what is meant by "VID1" and "VID0". Is "VID1" the inner (customer)
VLAN tag, and "VID0" the outer (service) VLAN tag, or "VID1" means the
actual VLAN ID 1?

And the bits 3:1 of VAWD1 (VLAN table access register) indicate a FID
field per VLAN. I cannot find the piece that you quoted in this manual.
But what I expect to happen for a Transparent Port is that the packets
are always classified to that port's PVID, and the VLAN Table is looked
up with that PVID. There, it will find the FID, which this driver
currently always configures as zero. In my manual's description, in the
"Transparent Port" chapter, it does explicitly say:

	VID0 and VID1 will store PVID as the default VID which is used
	to look up the VLAN table.

So I get the impression that the phrase "the VLAN table is not applicable"
is not quite correct, but I might be wrong...