linux-kernel - Re: [PATCH v1 1/2] dt-bindings: ethernet: eswin: add clock sampling control

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Message-ID: <aWKZvEW7rKFFwZLG@shell.armlinux.org.uk>
Date: Sat, 10 Jan 2026 18:26:04 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: lizhi2@...incomputing.com, devicetree@...r.kernel.org,
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, netdev@...r.kernel.org, pabeni@...hat.com,
	mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	ningyu@...incomputing.com, linmin@...incomputing.com,
	pinkesh.vaghela@...fochips.com, weishangjuan@...incomputing.com
Subject: Re: [PATCH v1 1/2] dt-bindings: ethernet: eswin: add clock sampling
 control

On Fri, Jan 09, 2026 at 07:27:54PM +0100, Andrew Lunn wrote:
> >    rx-internal-delay-ps:
> > -    enum: [0, 200, 600, 1200, 1600, 1800, 2000, 2200, 2400]
> > +    enum: [0, 20, 60, 100, 200, 400, 800, 1600, 2400]
> >  
> >    tx-internal-delay-ps:
> > -    enum: [0, 200, 600, 1200, 1600, 1800, 2000, 2200, 2400]
> > +    enum: [0, 20, 60, 100, 200, 400, 800, 1600, 2400]
> 
> You need to add some text to the Changelog to indicate why this is
> safe to do, and will not cause any regressions for DT blobs already in
> use. Backwards compatibility is very important and needs to be
> addressed.
> 
> > +  eswin,rx-clk-invert:
> > +    description:
> > +      Invert the receive clock sampling polarity at the MAC input.
> > +      This property may be used to compensate for SoC-specific
> > +      receive clock to data skew and help ensure correct RX data
> > +      sampling at high speed.
> > +    type: boolean
> 
> This does not make too much sense to me. The RGMII standard indicates
> sampling happens on both edges of the clock. The rising edge is for
> the lower 4 bits, the falling edge for the upper 4 bits. Flipping the
> polarity would only swap the nibbles around.

I'm going to ask a rather pertinent question. Why do we have this
eswin stuff in the kernel tree?

I've just been looking to see whether I can understand more about this,
and although I've discovered the TRM is available for the EIC7700:

https://github.com/eswincomputing/EIC7700X-SoC-Technical-Reference-Manual/releases

that isn't particularly helpful on its own.

There doesn't appear to be any device tree source files that describe
the hardware. The DT bindings that I can find seem to describe only
ethernet and USB. describe the ethernet and USB, and maybe sdhci.

I was looking for something that would lead me to what this
eswin,hsp-sp-csr thing is, but that doesn't seem to exist in our
DT binding documentation, nor does greping for "hsp.sp.csr" in
arch/*/boot/dts find anything.

So, we can't know what this "hsp" thing is to even know where to look
in the 80MiB of PDF documentation.

-- 
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