netdev - Re: [PATCH v4 net-next] net: phy: Add Edge-rate driver for Microsemi PHYs.

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Date:   Wed, 28 Sep 2016 18:16:53 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Raju Lakkaraju <Raju.Lakkaraju@...rosemi.com>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        f.fainelli@...il.com, Allan.Nielsen@...rosemi.com
Subject: Re: [PATCH v4 net-next] net: phy: Add Edge-rate driver for Microsemi
 PHYs.

> +Optional properties:
> +- vsc8531,vddmac	: The vddmac in mV.
> +- vsc8531,edge-slowdown	: % the edge should be slowed down relative to
> +			  the fastest possible edge time. Native sign
> +			  need not enter.
> +			  Edge rate sets the drive strength of the MAC
> +			  interface output signals.  Changing the drive
> +			  strength will affect the edge rate of the output
> +			  signal.  The goal of this setting is to help
> +			  reduce electrical emission (EMI) by being able
> +			  to reprogram drive strength and in effect slow
> +			  down the edge rate if desired.  Table 5 shows the

Hi Raju

There is no table five here? Is that a reference to a data sheet
table?

> +Example:
> +
> +        vsc8531_0: ethernet-phy@0 {
> +                compatible = "ethernet-phy-id0007.0570";
> +                vsc8531,vddmac		= /bits/ 16 <MSCC_VDDMAC_3300>;
> +                vsc8531,edge-slowdown	= /bits/ 8  <17>;

No, real values please:

                vsc8531,vddmac		= <2000>;
                vsc8531,edge-slowdown	= <21>;

The driver should then do the maths to figure out the nearest magic
value to write to the register, or complain the settings are out of
range with an -EINVAL.

FYI: No floating point maths are allowed in the kernel.

   Andrew