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

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Biju,

On Mon, Sep 19, 2022 at 1:10 PM Biju Das <biju.das.jz@xxxxxxxxxxxxxx> wrote:
> Mahadev Lad <prabhakar.mahadev-
> > lad.rj@xxxxxxxxxxxxxx>
> > On Mon, Sep 19, 2022 at 11:55 AM Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> > wrote:
> > > > -----Original Message-----
> > > > From: Lad, Prabhakar <prabhakar.csengg@xxxxxxxxx>
> > > > Sent: 19 September 2022 11:44
> > > > To: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> > > > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>; Magnus Damm
> > > > <magnus.damm@xxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>;
> > Krzysztof
> > > > Kozlowski <krzysztof.kozlowski+dt@xxxxxxxxxx>; linux-renesas-
> > > > soc@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-
> > > > kernel@xxxxxxxxxxxxxxx; Prabhakar Mahadev Lad <prabhakar.mahadev-
> > > > lad.rj@xxxxxxxxxxxxxx>
> > > > 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@xxxxxxxxxxxxxx>
> > > > wrote:
> > > > > Prabhakar Mahadev Lad <prabhakar.mahadev-
> > > > > > lad.rj@xxxxxxxxxxxxxx>
> > > > > > 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@xxxxxxxxxxxxxx>
> > > > > > 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@xxxxxxxxx> wrote:
> > > > > > > > > > From: Lad Prabhakar
> > > > > > > > > > <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > > > > > > > > >
> > > > > > > > > > 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?

> 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%7C55f37d25d74646611de908da9a2ecfac%
> > 7C53d82571da1947e49cb4625a166a4a2a%7C0%7C0%7C637991823087385873%7CUnkn
> > own%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwi
> > LCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=hP2u5NwutD8AhhrOrY6dPvlWW8PkB
> > g3skyTMXBJQaWc%3D&amp;reserved=0

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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