linux-kernel - Re: [PATCH v3 0/6] Add support to retrieve the bootstatus from watchdog for RZ/V2H(P) SoC

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Message-ID: <CA+V-a8tQ_tyxPn2pO=mSPVW2RffVhFz=CPCxR2pxXP1FLkcQcA@mail.gmail.com>
Date: Mon, 13 Jan 2025 12:40:35 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Biju Das <biju.das.jz@...renesas.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Wim Van Sebroeck <wim@...ux-watchdog.org>, 
	Guenter Roeck <linux@...ck-us.net>, Magnus Damm <magnus.damm@...il.com>, 
	Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v3 0/6] Add support to retrieve the bootstatus from
 watchdog for RZ/V2H(P) SoC

Hi Biju,

On Mon, Jan 13, 2025 at 11:38 AM Biju Das <biju.das.jz@...renesas.com> wrote:
>
> Hi Prabhakar,
>
> > -----Original Message-----
> > From: Prabhakar <prabhakar.csengg@...il.com>
> > Sent: 13 January 2025 11:24
> > Subject: [PATCH v3 0/6] Add support to retrieve the bootstatus from watchdog for RZ/V2H(P) SoC
> >
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Hi All,
> >
> > This patch series adds SYSCON support to retrieve boot status information for RZ/V2H(P) SoC.
> > Summary of Changes,
> >
> >     Clock:
> >         Add syscon compatible support to the CPG block in bindings and
> >         device trees.
> >
> >     Watchdog:
> >         Document the renesas,r9a09g057-syscon-wdt-errorrst property.
> >         Update the watchdog driver to fetch and report boot status via
> >         Error Reset Registers (CPG_ERROR_RSTm).
> >
> >     Device Tree:
> >         Add the syscon property to CPG and WDT nodes in R9A09G057 and
> >         R9A09G047 SoC DTSI.
> >
> > These changes enable the watchdog driver to identify boot sources like Power-on Reset and Watchdog
> > Reset, improving system diagnostics.
>
> This means that, we should assume U-boot/bootloader should not clear the WDT reset status bit.
>
> If they clear it, there should be a way to propagate it from u-boot/bootloader to linux,
> otherwise, we get wrong bootstatus in linux.
> But the clearing of watchdog status by one of the cases:
>
> 1) u-boot identify the boot source and clear the status bit
>
I agree, if the tf-a/u-boot clears the register, the bootstatus
reported by Linux will be in-correct.

Alternative solution, would be:

Let the TF-A create WDT nodes for us and add a property
`renesas,r9a09g057-wdt-bootstatus` and propagate the WDT nodes to
Linux.

renesas,r9a09g057-wdt-bootstatus = <0/1>;

0 -> Power on reset
1 -> WDT reset

Geert/Rob/Krzysztof - Is the proposed approach acceptable or is there
any alternative where this can be avoided.

Cheers,
Prabhakar