netdev - Re: [PATCH] net: phy: motorcomm: Fix the issue in the code regarding the incorrect use of time units

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Message-ID: <aQC01GDPr-WclcZS@shell.armlinux.org.uk>
Date: Tue, 28 Oct 2025 12:19:32 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Yi Cong <cong.yi@...ux.dev>, Frank.Sae@...or-comm.com,
	andrew+netdev@...n.ch, davem@...emloft.net, hkallweit1@...il.com,
	kuba@...nel.org, netdev@...r.kernel.org, stable@...r.kernel.org,
	yicong@...inos.cn
Subject: Re: [PATCH] net: phy: motorcomm: Fix the issue in the code regarding
 the incorrect use of time units

On Tue, Oct 28, 2025 at 01:07:34PM +0100, Andrew Lunn wrote:
> > > >  #define YT8521_CCR_RXC_DLY_EN			BIT(8)
> > > > -#define YT8521_CCR_RXC_DLY_1_900_NS		1900
> > > > +#define YT8521_CCR_RXC_DLY_1_900_PS		1900
> > >
> > > This could be down to interpretation.
> > >
> > > #define YT8521_CCR_RXC_DLY_1.900_NS		1900
> > >
> > > would be technically correct, but not valid for cpp(1). So the . is
> > > replaced with a _ .
> > >
> > > #define YT8521_CCR_RXC_DLY_1900_PS		1900
> > >
> > > would also be correct, but that is not what you have in your patch,
> > > you leave the _ in place.
> > 
> > Alright, I didn't realize that 1_950 represents 1.950;
> > I thought the underscores were used for code neatness,
> > making numbers like 900 and 1050 the same length, for example:
> > #define YT8521_RC1R_RGMII_0_900_PS
> > #define YT8521_RC1R_RGMII_1_050_PS
> > 
> > In that case, is my patch still necessary?
> 
> I think it is unnecessary.
> 
> If you want, you could add a comment which explains that the _ should
> be read as a .  However, this does appear elsewhere in Linux, it is
> one of those things you learn with time.

Hang on.

Is the "1900" 1.9ns or 1.9ps ?

If YT8521_CCR_RXC_DLY_1_900_NS means 1.9ns, and the value is in ps,
then surely if it's being renamed to _PS, then it _must_ become
YT8521_CCR_RXC_DLY_1900_NS, because 1.900ps is wrong?

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