netdev - Re: [PATCH net-next] net: phy: mscc: consolidate a common RGMII delay implementation

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Date:   Tue, 24 Mar 2020 16:13:40 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>
Subject: Re: [PATCH net-next] net: phy: mscc: consolidate a common RGMII delay implementation

On Tue, 24 Mar 2020 at 15:40, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Tue, Mar 24, 2020 at 02:48:37PM +0200, Vladimir Oltean wrote:
> > From: Vladimir Oltean <vladimir.oltean@....com>
> >
> > It looks like the VSC8584 PHY driver is rolling its own RGMII delay
> > configuration code, despite the fact that the logic is mostly the same.
> >
> > In fact only the register layout and position for the RGMII controls has
> > changed. So we need to adapt and parameterize the PHY-dependent bit
> > fields when calling the new generic function.
>
> Nice.
>
> > -static void vsc8584_rgmii_set_skews(struct phy_device *phydev)
> > -{
> > -     u32 skew_rx, skew_tx;
> > -
> > -     /* We first set the Rx and Tx skews to their default value in h/w
> > -      * (0.2 ns).
> > -      */
>
> I like seeing this comment. It makes it clear that
> PHY_INTERFACE_MODE_RGMII does not actually mean 0ns, but 0.2ns.  It
> also makes it clear that if PHY_INTERFACE_MODE_RGMII_ID,
> PHY_INTERFACE_MODE_RGMII_RXID or PHY_INTERFACE_MODE_RGMII_TXID is not
> given, the delay is set to something. We have had PHY drivers which
> get this wrong and leave the bootloader/strapping value in place.
>
> So if you can keep the comment in some form, that would be good.
>
> Thanks
>         Andrew

I find the comments fairly redundant since the code that does that is
already explicit, but anyway I'll send a v2 for the 0.2 ns thing.

Thanks,
-Vladimir