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

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Message-ID: <B91A794A-E822-4F27-8744-1D83C87D72FC@arinc9.com>
Date:   Thu, 15 Jun 2023 00:50:49 +0300
From:   Arınç ÜNAL <arinc.unal@...nc9.com>
To:     Vladimir Oltean <olteanv@...il.com>
CC:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        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>,
        "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>,
        Bartel Eerdekens <bartel.eerdekens@...stell8.be>,
        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 15 June 2023 00:43:13 EEST, Vladimir Oltean <olteanv@...il.com> wrote:
>On Wed, Jun 14, 2023 at 11:52:24PM +0300, Arınç ÜNAL wrote:
>> On 14.06.2023 19:42, Russell King (Oracle) 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).
>
>so far so good
>
>> > > 
>> > > The mt753x_bpdu_port_fw enum is universally used for trapping frames,
>> > > therefore rename it and the values in it to mt753x_port_fw.
>
>yeah, this part of the patch is not useful at all [ here ]
>
>> > > 
>> > > 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.
>
>redundant and useless information here - what's important here is that
>they're trapped, not where

Ok, will remove.

>
>> > > 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.
>
>I guess that the reader who isn't familiar with the hardware will never
>get to ask himself "is the unrelated R0E_MANG_FR bit set ok?", and the
>familiar reader can just look that up in the programming guides that are
>available, and see the default value and that the driver doesn't change it.
>
>So I just don't see how this bit of information is relevant in this
>patch. Sure, by all means, provide all context that helps the reader to
>understand the change, but at the same time: less is more.

Will remove.

>
>> > > 
>> > > 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.
>> > 
>> > 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?
>> 
>> I should do the enum renaming on my net-next series instead, as it's not
>> useful to what this patch fixes at all.
>
>please do so (assuming that the enum really has to be changed).
>
>also, if you're not really sure that this behavior has impacted any user
>(including yourself), I suppose there's also the option of fixing this in
>net-next as one of the earliest patches, independent from any other rework,
>so that in case there's a request to backport it to stable, it's possible.
>I remember having suggested this once already.

This impacts the devices of the company I work with and Bartel's, so I would like this on the stable kernels immediately.

Arınç