linux-kernel - Re: [PATCH 1/2] dt-bindings: i2c: omap: Add mux-states property

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Message-ID: <20250319123256.3482063f@akair>
Date: Wed, 19 Mar 2025 12:32:56 +0100
From: Andreas Kemnade <andreas@...nade.info>
To: Rob Herring <robh@...nel.org>
Cc: "Ing. Josua Mayer" <josua.mayer@....eu>, Jayesh Choudhary
 <j-choudhary@...com>, vigneshr@...com, andi.shyti@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, linux-kernel@...r.kernel.org,
 aaro.koskinen@....fi, khilman@...libre.com, rogerq@...nel.org,
 tony@...mide.com, jmkrzyszt@...il.com, linux-omap@...r.kernel.org,
 linux-i2c@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: i2c: omap: Add mux-states property

Am Tue, 18 Mar 2025 17:18:29 -0500
schrieb Rob Herring <robh@...nel.org>:

> On Tue, Mar 18, 2025 at 2:55 PM Ing. Josua Mayer <josua.mayer@....eu> wrote:
> >
> > Hi Jayesh,
> >
> > Am 18.03.25 um 11:36 schrieb Jayesh Choudhary:  
> > > Add mux controller support for when the I2C lines are muxed after
> > > signals come out of SoC and before they go to any client.
> > >
> > > Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> > > ---
> > >   Documentation/devicetree/bindings/i2c/ti,omap4-i2c.yaml | 6 ++++++
> > >   1 file changed, 6 insertions(+)  
> >
> > Is there any chance for this to be generic across any i2c controller
> > regardless of SoC in use?
> > Is this perhaps also generic to any device in dts,
> > similar to assigned-clocks?  
> 
> $ git grep assigned-clocks arch/ | wc -l
> 2097
> 
> >
> > E.g. in k3-am642-hummingboard-t-{pcie,usb3}.dts we have a mux on the
> > carrier board switching a serdes lane between two different connectors.
> > It would make sense for pcie and usb phy nodes to delay probe in a
> > similar fashion.
> > The same may hold true for other buses muxed at boot-time or based on
> > assembly options or extension cards.  
> 
> $ git grep mux-states arch/
> arch/arm64/boot/dts/ti/k3-j7200-common-proc-board.dts:
> mux-states = <&mux0 1>;
> arch/arm64/boot/dts/ti/k3-j721s2-common-proc-board.dts:
> mux-states = <&mux0 1>;
> arch/arm64/boot/dts/ti/k3-j721s2-common-proc-board.dts:
> mux-states = <&mux1 1>;
> arch/arm64/boot/dts/ti/k3-j784s4-j742s2-evm-common.dtsi:
>  mux-states = <&mux1 1>;
> 
> I'm not convinced it is common enough to allow everywhere.
> 
strange logic. It is not in there, because it is not allowed/supported
and some quirk maybe is added elsewhere, e.g. in bootloader or private
kernel branch.
So you cannot say whether such a case is common engough by looking what
is *now* in the dtb.

Regards,
Andreas