Re: [PATCH net-next 0/3] net: phy: dp83822: Add support for changing the MAC series termination

[Dimitri Fedrau]

Am Fri, Mar 07, 2025 at 02:39:32PM +0100 schrieb Andrew Lunn:
> On Fri, Mar 07, 2025 at 11:30:00AM +0100, Dimitri Fedrau via B4 Relay wrote:
> > The dp83822 provides the possibility to set the resistance value of the
> > the MAC series termination. Modifying the resistance to an appropriate
> > value can reduce signal reflections and therefore improve signal quality.
> 
> I have some dumb questions....
> 
> By referring to MAC from the perspective of the PHY, do you mean the
> termination of the bus between the MAC and the PHY? The SGMII SERDES,
> or RGMII?
>
- Yes, the perspective is from the PHY.
- Yes, but only the outputs towards the MAC. Resistors can be saved on
  the PCB when they are integrated into the PHY.
- The PHY is able to operate with RGMII, RMII and MII.

Should I rename then "mac-series-termination-ohms" to
"output-mac-series-termination-ohms" or similar ?

> I'm assuming the terminology is direct from the datasheet of the PHY?
> But since this is a bit of a niche area, no other PHY driver currently
> supports anythings like this, the terminology is not well known. So it
> would be good to expand the description, to make it really clear what
> you are talking about, so if anybody else wants to add the same
> feature, they make use of the property, not add a new property.

The datasheet calls it MAC impedance control, that is what someone might
want to achieve when selecting the proper resistance value. I named it
"mac-series-termination-ohms" instead to make sure what is done to
achieve impedance matching.

Should I add the proper description in the bindings ? Description of the
properties are somehow short. However will expand the description.

Best regards,
Dimitri Fedrau