linux-kernel - Re: [PATCH v7 5/7] arm64: dts: ti: k3-j784s4-mcu: Add the mcu domain watchdog instances

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Date:   Fri, 6 Oct 2023 07:01:22 -0500
From:   Nishanth Menon <nm@...com>
To:     "J, KEERTHY" <j-keerthy@...com>
CC:     <robh+dt@...nel.org>, <vigneshr@...com>, <conor+dt@...nel.org>,
        <kristo@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <u-kumar1@...com>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 5/7] arm64: dts: ti: k3-j784s4-mcu: Add the mcu domain
 watchdog instances

On 17:22-20231006, J, KEERTHY wrote:
> 
> 
> On 10/6/2023 5:04 PM, Nishanth Menon wrote:
> > On 09:58-20231006, Keerthy wrote:
> > > There are totally 2 instances of watchdog module in MCU domain.
> > > These instances are coupled with the MCU domain R5F instances.
> > 
> > > Disabling them as they are not used by Linux.
> > Device tree is hardware description - not tied to how Linux uses it.
> > 
> > Reason these wdts are disabled by default is because they are tightly
> > coupled with R5Fs.
> > 
> > > 
> > > Signed-off-by: Keerthy <j-keerthy@...com>
> > > ---
> > >   .../boot/dts/ti/k3-j784s4-mcu-wakeup.dtsi     | 24 +++++++++++++++++++
> > >   1 file changed, 24 insertions(+)
> > > 
> > > diff --git a/arch/arm64/boot/dts/ti/k3-j784s4-mcu-wakeup.dtsi b/arch/arm64/boot/dts/ti/k3-j784s4-mcu-wakeup.dtsi
> > > index a7b5c4cb7d3e..809a0b1cf038 100644
> > > --- a/arch/arm64/boot/dts/ti/k3-j784s4-mcu-wakeup.dtsi
> > > +++ b/arch/arm64/boot/dts/ti/k3-j784s4-mcu-wakeup.dtsi
> > > @@ -714,4 +714,28 @@
> > >   		ti,esm-pins = <63>;
> > >   		bootph-pre-ram;
> > >   	};
> > > +
> 
> Nishanth,
> 
> Below i have addressed the coupling with R5Fs & MCU domains watcdogs.
> 
> > > +	/*
> > > +	 * The 2 RTI instances are couple with MCU R5Fs so keeping them
> > > +	 * disabled as these will be used by their respective firmware

This description is best in the commit message

> > > +	 */
> > > +	mcu_watchdog0: watchdog@...00000 {
> > > +		compatible = "ti,j7-rti-wdt";
> > > +		reg = <0x00 0x40600000 0x00 0x100>;
> > > +		clocks = <&k3_clks 367 1>;
> > > +		power-domains = <&k3_pds 367 TI_SCI_PD_EXCLUSIVE>;
> > > +		assigned-clocks = <&k3_clks 367 0>;
> > > +		assigned-clock-parents = <&k3_clks 367 4>;
> > > +		status = "disabled";
> > > +	};
> > > +
> > > +	mcu_watchdog1: watchdog@...10000 {
> > > +		compatible = "ti,j7-rti-wdt";
> > > +		reg = <0x00 0x40610000 0x00 0x100>;
> > > +		clocks = <&k3_clks 368 1>;
> > > +		power-domains = <&k3_pds 368 TI_SCI_PD_EXCLUSIVE>;
> > > +		assigned-clocks = <&k3_clks 368 0>;
> > > +		assigned-clock-parents = <&k3_clks 368 4>;
> > 
> > Please DONOT ignore the review comments - I did ask the documentation in
> > dts as well. reason being that this is what people will see rather than
> > dig up the commit log. it should be intutive when reading the dts why
> > nodes are disabled by default Vs the standard of leaving it enabled by
> > default. Given esp that these peripherals do not have anything to do
> > with board semantics (pinmux or something similar) to be complete.
> 
> As mentioned above. I added single comment for addressing both the
> watchdogs.

I missed it completely. Now that I think of it, I seem to have missed
having seen it in previous rev reviews as well, and there is a reason
for it: See [1] clarifying comment - nodes reserved for firmware usage
have convention of "reserved" as status and documentation immediately
above the status to help clarify the reason in-context. That is more
readable than having to scroll up to find the rationale.

[1] https://lore.kernel.org/all/20231006114422.avymeap7h5ocs6zq@dreadlock/

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D