RE: [PATCH] arm64: dts: renesas: rzg2ul-smarc-som: Drop enabling wdt2

From: Biju Das <biju.das.jz@bp.renesas.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>,
	Magnus Damm <magnus.damm@gmail.com>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	"linux-renesas-soc@vger.kernel.org" 
	<linux-renesas-soc@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>
Subject: RE: [PATCH] arm64: dts: renesas: rzg2ul-smarc-som: Drop enabling wdt2
Date: Mon, 19 Sep 2022 11:43:04 +0000	[thread overview]
Message-ID: <OS0PR01MB59223965328DAFEB17C42710864D9@OS0PR01MB5922.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <CAMuHMdXCyTGbwp9F-PEcn3qxapDMU+UEY2=RVNy8p9fNesKepA@mail.gmail.com>

Hi Geert,

> Subject: Re: [PATCH] arm64: dts: renesas: rzg2ul-smarc-som: Drop
> enabling wdt2
> 
> Hi Biju,
> 
> On Mon, Sep 19, 2022 at 1:10 PM Biju Das <biju.das.jz@bp.renesas.com>
> wrote:
> > Mahadev Lad <prabhakar.mahadev-
> > > lad.rj@bp.renesas.com>
> > > On Mon, Sep 19, 2022 at 11:55 AM Biju Das
> > > <biju.das.jz@bp.renesas.com>
> > > wrote:
> > > > > -----Original Message-----
> > > > > From: Lad, Prabhakar <prabhakar.csengg@gmail.com>
> > > > > Sent: 19 September 2022 11:44
> > > > > To: Biju Das <biju.das.jz@bp.renesas.com>
> > > > > Cc: Geert Uytterhoeven <geert@linux-m68k.org>; Magnus Damm
> > > > > <magnus.damm@gmail.com>; Rob Herring <robh+dt@kernel.org>;
> > > Krzysztof
> > > > > Kozlowski <krzysztof.kozlowski+dt@linaro.org>; linux-renesas-
> > > > > soc@vger.kernel.org; devicetree@vger.kernel.org; linux-
> > > > > kernel@vger.kernel.org; Prabhakar Mahadev Lad
> > > > > <prabhakar.mahadev- lad.rj@bp.renesas.com>
> > > > > Subject: Re: [PATCH] arm64: dts: renesas: rzg2ul-smarc-som:
> Drop
> > > > > enabling wdt2
> > > > >
> > > > > On Mon, Sep 19, 2022 at 11:15 AM Biju Das
> > > > > <biju.das.jz@bp.renesas.com>
> > > > > wrote:
> > > > > > Prabhakar Mahadev Lad <prabhakar.mahadev-
> > > > > > > lad.rj@bp.renesas.com>
> > > > > > > Subject: Re: [PATCH] arm64: dts: renesas: rzg2ul-smarc-
> som:
> > > Drop
> > > > > > > enabling wdt2
> > > > > > >
> > > > > > > Hi Biju,
> > > > > > >
> > > > > > > On Mon, Sep 19, 2022 at 12:06 PM Biju Das
> > > > > > > <biju.das.jz@bp.renesas.com>
> > > > > > > wrote:
> > > > > > > > > On Sun, Sep 18, 2022 at 10:04 AM Geert Uytterhoeven
> > > > > > > > > <geert@linux- m68k.org> wrote:
> > > > > > > > > > On Wed, Sep 14, 2022 at 3:43 PM Prabhakar
> > > > > > > > > <prabhakar.csengg@gmail.com> wrote:
> > > > > > > > > > > From: Lad Prabhakar
> > > > > > > > > > > <prabhakar.mahadev-lad.rj@bp.renesas.com>
> > > > > > > > > > >
> > > > > > > > > > > WDT CH2 is specifically to check the operation of
> > > > > > > > > > > Cortex-
> > > > > M33
> > > > > > > CPU
> > > > > > > > > so
> > > > > > > > > > > don't enable WDT2 by default.
> > > > > > > > > > >
> > > > > > > > > For consistency I'll drop enabling WDT2 from the
> > > > > > > > > RZ/G2L{C}
> > > > > too.
> > > > > > > >
> > > > > > > > Does remove unused clocks turn off WDT2 clock during
> late
> > > init??
> > > > > > > >
> > > > > > > > If that is the case, we should remove entries from clock
> > > table
> > > > > as
> > > > > > > well?
> > > > > > >
> > > > > > > Or add it to *_crit_mod_clks[]?
> > > > > > >
> > > > > > > Note that drivers/clk/renesas/r9a07g043-cpg.c creates wdt2
> > > > > > > clocks and resets, so that should probably be moved inside
> > > > > > > the #ifdef
> > > > > > > CONFIG_ARM64 section.
> > > > > >
> > > > > Yes we dont want it to be listed on RZ/Five.
> > > >
> > > > OK, So this patch [1] will break existing RZ/G2UL till we have
> clk
> > > changes suggested by Geert.
> > > >
> > > No it won't, patch [1] just disables enabling wdt2 on A55. Whereas
> > > Geert is suggesting adding wdt2 clk R9A07G043_WDT2_PCLK (and also
> > > R9A07G043_WDT2_CLK?)  to crit_mod_clks so that we dont disable
> them
> > > in
> > > A55 (currently we dont have any scenario where M33 is up with WDT2
> > > and patch [1] is breaking it). Also Geert's other suggestion was
> to
> > > add the WDT2 clocks under ARM64 as we dont want them to be visible
> > > under RZ/Five (where wdt2 is not present).
> > >
> > > Or is it that I am missing something?
> >
> > It all depends upon whether remove unused clocks turn off WDT2 clock
> > during late boot process.
> >
> > I guess, since we have wdt2 entries in clock table, it will turn off
> > WDT clock, since you have disable it from DT( it becomes unused).
> 
> AFAIU, the WDT cannot trigger when the clock is stopped, so RZ/G2UL
> should be fine?

If CA-33 turning on WDT clock (eg:- u-boot loading and booting CA-33) and
Later it will be disabled by CA-55 during late boot, then we will have problem.
Then WDT on CA-33 won't work.

Currently as far as I know, no one is using CA-33 with mainline code, So it is ok.

Cheers,
Biju

> 
> > By adding critical clocks, it won't turn off the WDT clock.
> 
> > > [1]
> > >
> https://jpn01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.
> > > kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fnext%2Flinux-
> > > next.git%2Fcommit%2F%3Fh%3Dnext-
> > >
> 20220919%26id%3D31989ece707adc453eb9f4f019fdac118f8fee72&amp;data=05
> > > %7
> > >
> C01%7Cbiju.das.jz%40bp.renesas.com%7C55f37d25d74646611de908da9a2ecfa
> > > c%
> > >
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> > > kn
> > >
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> > > wi
> > >
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> > > kB
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> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a
> hacker. But when I'm talking to journalists I just say "programmer" or
> something like that.
>                                 -- Linus Torvalds