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-a8sCTNdoxNksd_N-j7i_VJq-qL9_cv22HT7DXE-M39XLmA@mail.gmail.com>
Date: Mon, 13 Jan 2025 16:29:13 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Guenter Roeck <linux@...ck-us.net>, Biju Das <biju.das.jz@...renesas.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Wim Van Sebroeck <wim@...ux-watchdog.org>, 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 Guenter,

On Mon, Jan 13, 2025 at 4:08 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 1/13/25 04:40, Lad, Prabhakar wrote:
> > 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.
> >
>
> I would rephrase that: Today, the boot status is _always_ incorrect if a reboot
> was triggered by a watchdog reset. After this patch, it will be correct unless
> the boot loader resets the status bit.
>
Agreed.

> > 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>;
> >
>
> That would require both a property change as well as a change in the bootloader.
> I suspect it would also be inappropriate as standard property and would have
> to be passed as 'chosen' property (if that is even permitted) or as command line
> argument.
>
> Either case, if the boot loader has to be changed anyway, why not just tell it
> to leave the boot status alone ?
>
It can be done, I think Biju is concerned about the user clearing it,
maybe using the `mw` command or the Linux CPG driver clearing it
during the probe.

Cheers,
Prabhakar