linux-kernel - RE: [PATCH] clk: renesas: r9a07g044: Add WDT2 clocks to critical list

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Date:   Wed, 5 Oct 2022 08:27:40 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
CC:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: RE: [PATCH] clk: renesas: r9a07g044: Add WDT2 clocks to critical list

Hi Geert and Prabhakar,

> Subject: RE: [PATCH] clk: renesas: r9a07g044: Add WDT2 clocks to
> critical list
> 
> Hi Prabhakar,
> 
> > Subject: Re: [PATCH] clk: renesas: r9a07g044: Add WDT2 clocks to
> > critical list
> >
> > Hi Biju,
> >
> > On Mon, Sep 19, 2022 at 2:52 PM Biju Das
> <biju.das.jz@...renesas.com>
> > wrote:
> > >
> > > Hi Prabhakar,
> > >
> > > > Subject: Re: [PATCH] clk: renesas: r9a07g044: Add WDT2 clocks to
> > > > critical list
> > > >
> > > > Hi Biju,
> > > >
> > > > On Mon, Sep 19, 2022 at 2:35 PM Biju Das
> > > > <biju.das.jz@...renesas.com>
> > > > wrote:
> > > > >
> > > > > Hi Prabhakar,
> > > > >
> > > > > > Subject: [PATCH] clk: renesas: r9a07g044: Add WDT2 clocks to
> > > > > > critical list
> > > > > >
> > > > > > From: Lad Prabhakar <prabhakar.mahadev-
> lad.rj@...renesas.com>
> > > > > >
> > > > > > Add the WDT2 clocks to r9a07g044_crit_mod_clks[] list as WDT
> > CH2
> > > > is
> > > > > > specifically to check the operation of Cortex-M33 CPU on the
> > > > > > RZ/{G2L, G2LC, V2L} SoCs and we dont want to turn off the
> > clocks
> > > > of
> > > > > > WDT2 if it isn't enabled by Cortex-A55.
> > > > > >
> > > > > > This patch is in preparation to disable WDT CH2 from the
> > RZ/G2L
> > > > > > (alike
> > > > > > SoCs) DTS/I by default.
> > > > > >
> > > > > > Reported-by: Biju Das <biju.das.jz@...renesas.com>
> > > > > > Signed-off-by: Lad Prabhakar
> > > > > > <prabhakar.mahadev-lad.rj@...renesas.com>
> > > > > > ---
> > > > > >  drivers/clk/renesas/r9a07g044-cpg.c | 2 ++
> > > > > >  1 file changed, 2 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/clk/renesas/r9a07g044-cpg.c
> > > > > > b/drivers/clk/renesas/r9a07g044-cpg.c
> > > > > > index 02a4fc41bb6e..cf9b1bd73792 100644
> > > > > > --- a/drivers/clk/renesas/r9a07g044-cpg.c
> > > > > > +++ b/drivers/clk/renesas/r9a07g044-cpg.c
> > > > > > @@ -412,6 +412,8 @@ static const unsigned int
> > > > > > r9a07g044_crit_mod_clks[] __initconst = {
> > > > > >       MOD_CLK_BASE + R9A07G044_GIC600_GICCLK,
> > > > > >       MOD_CLK_BASE + R9A07G044_IA55_CLK,
> > > > > >       MOD_CLK_BASE + R9A07G044_DMAC_ACLK,
> > > > > > +     MOD_CLK_BASE + R9A07G044_WDT2_PCLK,
> > > > > > +     MOD_CLK_BASE + R9A07G044_WDT2_CLK,
> > > > >
> > > > > Do we need to turn on this clock unnecessarily?
> > > > >
> > > > No, this is in preparation to disable WDT2 by default from
> > RZ/G2L{C}
> > > > DTS/I.
> > >
> > > But that will make WDT2 device is not enabled, but unnecessarily
> the
> > clk is on.
> > >
> > Agreed the clocks will be ON, but didnt we agree earlier for
> > r9a07g043-cpg.c?
> 
> Yep, still we have a chance to conclude, whether we need to make this
> clk always on, if it is not enabled and there is no use case for wdt2
> controlling from CA-55??
> 

I got confirmation that that using WDT2 from CA55 is prohibited.
WDT2 is only for CM33.

With CPG register, we can select whether CM33 to trigger CM33 cpu reset, or trigger system reset
when WDT2 overflows.

If WDT2 is used by CA55, it may result in unexpected behaviour.

So we may need to take WDT2 entries from binding + dtsi + clock table??

Or

Added it to critical clock list, to avoid changes in binding + dtsi + clock table
at the expense of turning on the WDT2 clk unnecessarily.

Please share your views.

Cheers,
Biju