netdev - Re: [net-next,PATCH 3/3] net: phy: realtek: Add property to enable SSC

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Message-ID: <aTB0x6JGcGUM04UX@shell.armlinux.org.uk>
Date: Wed, 3 Dec 2025 17:35:03 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: Marek Vasut <marek.vasut@...lbox.org>, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Aleksander Jan Bajkowski <olek2@...pl>,
	Andrew Lunn <andrew@...n.ch>, Conor Dooley <conor+dt@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Michael Klein <michael@...sekall.de>,
	Paolo Abeni <pabeni@...hat.com>, Rob Herring <robh@...nel.org>,
	devicetree@...r.kernel.org
Subject: Re: [net-next,PATCH 3/3] net: phy: realtek: Add property to enable
 SSC

On Wed, Dec 03, 2025 at 02:34:30PM +0200, Vladimir Oltean wrote:
> On Wed, Dec 03, 2025 at 10:18:35AM +0000, Russell King (Oracle) wrote:
> > On Sun, Nov 30, 2025 at 01:58:34AM +0100, Marek Vasut wrote:
> > > Add support for spread spectrum clocking (SSC) on RTL8211F(D)(I)-CG,
> > > RTL8211FS(I)(-VS)-CG, RTL8211FG(I)(-VS)-CG PHYs. The implementation
> > > follows EMI improvement application note Rev. 1.2 for these PHYs.
> > > 
> > > The current implementation enables SSC for both RXC and SYSCLK clock
> > > signals. Introduce new DT property 'realtek,ssc-enable' to enable the
> > > SSC mode.
> > 
> > Should there be separate properties for CLKOUT SSC enable and RXC SSC
> > enable?
> 
> That's what we're trying to work out. I was going to try and give an
> example (based on stmmac) why you wouldn't want RXC SSC but you'd still
> want CLKOUT SSC, but it doesn't seem to hold water based on your feedback.
> Having one device tree property to control both clocks is a bit simpler.

The problem I see is that if we introduce a single property for both,
we then need to maintain this single property ad infinitum. If we
later find that we need separate control, we could end up with three
properties - the combined one, and two for individual controls.

If we are to go with a single property, then I think we should have at
least discussed what we would do if we need separate control.

If we go with two properties now, then we don't have to consider this,
and we will only ever have the two properties rather than three.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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