linux-kernel - Re: [PATCH net-next 2/2] net: dsa: microchip: add KSZ8 change_tag

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Message-ID: <CAHvy4Aq0-9+Z9oCSSb=18GHduAfciAzritGb6yhNy1xvO8gNkg@mail.gmail.com>
Date: Mon, 19 Aug 2024 15:21:51 +0200
From: Pieter <vtpieter@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Vladimir Oltean <olteanv@...il.com>, Woojung Huh <woojung.huh@...rochip.com>, 
	UNGLinuxDriver@...rochip.com, 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>, 
	Russell King <linux@...linux.org.uk>, Pieter Van Trappen <pieter.van.trappen@...n.ch>, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: dsa: microchip: add KSZ8
 change_tag_protocol support

Hi Andrew,

> > Previously I could not use DSA because of the macb driver limitation, now
> > fixed (max_mtu increase, submitted here). Once I got that working, I notice
> > that full DSA was not a compatible use case for my board because of
> > requiring the conduit interface to behave as a regular ethernet interface.
> > So it's really the unmanaged switch case, which I though I motivated well in
> > the patch description here (PHY library, ethtool and switch WoL management).
>
> If its an unmanaged switch, you don't need DSA, or anything at all
> other than MACB. Linux is just a plain host connected to a switch. It
> is a little unusual that the switch is integrated into the same box,
> rather than being a patch cable away, bit linux does not really see
> this difference compared to any other unmanaged switch.

That's true in theory but not in practice because without DSA I can't use
the ksz_spi.c driver which gives me access to the full register set. I need
this for the KSZ8794 I'm using to:
- apply the EEE link drop erratum from ksz8795.c
- active port WoL which is connected through its PME_N pin
- use iproute2 for PHY and connection debugging (link up/down,
  packets statistics etc.)

If there's another way to accomplish the above without DSA, I'd be
happy to learn about it.

Cheers, Pieter