linux-kernel - Re: [PATCH net-next v3 3/5] net: pcs: add new PCS driver for altera TSE PCS

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Message-ID: <Y1kihVfwglzOD2uE@lunn.ch>
Date:   Wed, 26 Oct 2022 14:05:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     Sean Anderson <seanga2@...il.com>, davem@...emloft.net,
        Rob Herring <robh+dt@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH net-next v3 3/5] net: pcs: add new PCS driver for altera
 TSE PCS

> > > +	/* This PCS seems to require a soft reset to re-sync the
> > > AN logic */
> > > +	tse_pcs_reset(tse_pcs);  
> > 
> > This is kinda strange since c22 phys are supposed to reset the other
> > registers to default values when BMCR_RESET is written. Good thing
> > this is a PCS...
> 
> Indeed. This soft reset will not affect the register configuration, it
> will only reset all internal state machines.
> 
> The datasheet actually recommends performing a reset after any
> configuration change...

The Marvell PHYs work like this. Many of its registers won't take
effect until you do a soft reset. I think the thinking behind this is
that changing many registers is disruptive to the link and slow. It
takes over a second to perform auto-neg etc. So ideally you want to
make all your register changes, and then trigger them into operation.
And a soft reset is this trigger.

    Andrew