netdev - Re: [PATCH] net: phy: marvell-88q2xxx: add driver for the Marvell 88Q2220 PHY

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Message-ID: <20240105222033.GA40773@debian>
Date: Fri, 5 Jan 2024 23:20:33 +0100
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Stefan Eichenberger <eichest@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: marvell-88q2xxx: add driver for the Marvell
 88Q2220 PHY

Am Fri, Jan 05, 2024 at 05:06:53PM +0100 schrieb Andrew Lunn:
> > Hi Andrew,
> > 
> > > Do we need to reduce the init sequence? Since this is all undocumented
> > > magic which nobody understands, it would be safer to just keep with
> > > the Marvell vendor crap code dump. Unless we really do need to change
> > > it.
> > >
> > You are right, it would be safer to use the vendor code. But when
> > looking at the vendor code, the init sequence changed a lot from rev. B0
> > to rev. B1 of the PHY. There are some additional register writes, but
> > mostly the order of the register writes changed. I don't know if this is
> > going to be worse in the future. Maintaining different revisions will
> > probably take some effort or at least result in bloated code. We probably
> > don't need all of the init sequence. I'm not sure how to deal with it,
> > keeping the init sequence at a minimum is probably a good idea.
> 
> Is the revision in the lower nibble of the ID register? We can handle
> them as different PHYs, each gets its own init code, and share what
> can be shared in helper functions.
>
Yes, lowest four bits. Handling them as different PHYs would definitely
help maintaining PHY revisions. Still there is the problem with this
huge undocumented init sequence. Is this going to be accepted ? Didn't
see such a long undocumented init sequence in any other phy driver.

> 	Andrew

Best regards,
Dimitri