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

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Message-ID: <20200324134047.GY3819@lunn.ch>
Date:   Tue, 24 Mar 2020 14:40:47 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, f.fainelli@...il.com,
        hkallweit1@...il.com, antoine.tenart@...tlin.com
Subject: Re: [PATCH net-next] net: phy: mscc: consolidate a common RGMII
 delay implementation

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