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

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Message-ID: <9e5cc632-3058-46b2-8920-30c521eb1bbd@lunn.ch>
Date: Mon, 19 Aug 2024 15:27:17 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Pieter <vtpieter@...il.com>
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

On Mon, Aug 19, 2024 at 03:21:51PM +0200, Pieter wrote:
> 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.)

Then it is not an unmanaged switch. You are managing it.

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

Its go back to the beginning. Why cannot use you DSA, and use it as a
manage switch? None of your use-cases above are prevented by DSA.

	Andrew