linux-kernel - Re: [PATCH 0/2] J722S: DT Node cleanup for serdes0 and serdes1

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Message-ID: <79ef7f50-22d5-4c40-ae28-02bf297ca79c@ti.com>
Date: Mon, 14 Apr 2025 18:30:53 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Nishanth Menon <nm@...com>
CC: Siddharth Vadapalli <s-vadapalli@...com>, <vigneshr@...com>,
        <kristo@...nel.org>, <robh@...nel.org>, <krzk+dt@...nel.org>,
        <conor+dt@...nel.org>, <u-kumar1@...com>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <srk@...com>
Subject: Re: [PATCH 0/2] J722S: DT Node cleanup for serdes0 and serdes1

On Mon, Apr 14, 2025 at 07:09:30AM -0500, Nishanth Menon wrote:

Hello Nishanth,

> On 10:57-20250412, Siddharth Vadapalli wrote:
> > Hello,
> > 
> > This series is based on the following series:
> > https://patchwork.kernel.org/project/linux-arm-kernel/cover/20250408103606.3679505-1-s-vadapalli@ti.com/
> > Based on the discussion in the above series which disabled 'serdes_wiz0'
> > and 'serdes_wiz1' nodes in the SoC file and enabled them in the board
> > file, Udit pointed out that it wasn't necessary to disable 'serdes0' and
> > 'serdes1' in the SoC file anymore, since that is not a working
> > configuration - serdes_wizX enabled and serdesX disabled doesn't work.
> > 
> > Hence, this series aims to cleanup the serdesX nodes after the changes
> > made by the above series.
> > 
> > Regards,
> > Siddharth.
> > 
> > Siddharth Vadapalli (2):
> >   arm64: dts: ti: k3-j722s-main: don't disable serdes0 and serdes1
> >   arm64: dts: ti: k3-j722s-evm: drop redundant status within
> >     serdes0/serdes1
> > 
> >  arch/arm64/boot/dts/ti/k3-j722s-evm.dts   | 2 --
> >  arch/arm64/boot/dts/ti/k3-j722s-main.dtsi | 4 ----
> >  2 files changed, 6 deletions(-)
> > 
> > -- 
> > 2.34.1
> > 
> 
> 
> I do not understand the logic here. serdes cannot operate without wiz
> nodes, correct? why would we leave serdes on by default?

Yes, serdesX requires serdes_wizX, but at the same time, serdesX is the
child node of serdes_wizX. Therefore, without enabling serdes_wizX, we
cannot enable serdesX.

Prior to this series, but with the dependent series at:
https://patchwork.kernel.org/project/linux-arm-kernel/cover/20250408103606.3679505-1-s-vadapalli@ti.com/
applied, the nodes look like:

	serdes_wizX {
		...
		status = "disabled";

		serdesX {
			...
			status = "disabled";
		};
	};

The dependent series fixes 'serdes_wizX' by disabling it in the SoC file
k3-j722s-main.dtsi. But after the fix, we have a 'status = "disabled";'
within the serdesX node which isn't required since:
a) serdes_wizX enabled but serdesX disabled is non-functional and
unusable
b) serdes_wizX disabled in DT implies that serdesX is also disabled

Regards,
Siddharth.