netdev - Re: [PATCH net v4 5/7] net: dsa: mt7530: fix handling of LLDP frames

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Date: Thu, 15 Jun 2023 14:45:27 +0200
From: Bartel Eerdekens <bartel.eerdekens@...stell8.be>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: arinc9.unal@...il.com, Arınç ÜNAL <arinc.unal@...nc9.com>, 
	Daniel Golle <daniel@...rotopia.org>, Landen Chao <Landen.Chao@...iatek.com>, 
	DENG Qingfang <dqfext@...il.com>, Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>, 
	Florian Fainelli <f.fainelli@...il.com>, Vladimir Oltean <olteanv@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Frank Wunderlich <frank-w@...lic-files.de>, mithat.guner@...ont.com, erkin.bozoglu@...ont.com, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net v4 5/7] net: dsa: mt7530: fix handling of LLDP frames

On Wed, Jun 14, 2023 at 6:42 PM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Mon, Jun 12, 2023 at 10:59:43AM +0300, arinc9.unal@...il.com wrote:
> > From: Arınç ÜNAL <arinc.unal@...nc9.com>
> >
> > LLDP frames are link-local frames, therefore they must be trapped to the
> > CPU port. Currently, the MT753X switches treat LLDP frames as regular
> > multicast frames, therefore flooding them to user ports. To fix this, set
> > LLDP frames to be trapped to the CPU port(s).
> >
> > The mt753x_bpdu_port_fw enum is universally used for trapping frames,
> > therefore rename it and the values in it to mt753x_port_fw.
> >
> > For MT7530, LLDP frames received from a user port will be trapped to the
> > numerically smallest CPU port which is affine to the DSA conduit interface
> > that is up.
> >
> > For MT7531 and the switch on the MT7988 SoC, LLDP frames received from a
> > user port will be trapped to the CPU port that is affine to the user port
> > from which the frames are received.
> >
> > The bit for R0E_MANG_FR is 27. When set, the switch regards the frames with
> > :0E MAC DA as management (LLDP) frames. This bit is set to 1 after reset on
> > MT7530 and MT7531 according to the documents MT7620 Programming Guide v1.0
> > and MT7531 Reference Manual for Development Board v1.0, so there's no need
> > to deal with this bit. Since there's currently no public document for the
> > switch on the MT7988 SoC, I assume this is also the case for this switch.
> >
> > Fixes: b8f126a8d543 ("net-next: dsa: add dsa support for Mediatek MT7530 switch")
>
>
> Patch 4 claims to be a fix for this commit, and introduces one of these
> modifications to MT753X_BPC, which this patch then changes.

Let me chime in on this one, as mentioned by Arinç, I am one of the
requesters of having this patch (and patch 4).
Patch 4 enables the trapping of BPDU's to the CPU, being STP (Spanning
Tree) frames. Maybe that should be mentioned, to be clear.

>
> On the face of it, it seems this patch is actually a fix to patch 4 as
> well as the original patch, so does that mean that patch 4 only half
> fixes a problem?

This patch then also adds trapping for LLDP frames (Link Layer
Discovery Protocol) which is a completely different protocol.
But both rely on trapping frames, instead of forwarding them. So
that's why the enum was changed, to be named generic.


> And I just can't be bothered trying to parse the commit messages
> anymore.
>

I do agree some parts of the commit message could be omitted.
Especially the part of the R0E_MANG_FR, as it just describes a default
reset state of a register.
But it adds confusion mentioning it, as it is not even used in the patch itself.


Bartel