linux-kernel - Re: [PATCHv1 3/3] clk: meson: g12a: set cpu clock divider flags too CLK_IS

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Date:   Mon, 17 Feb 2020 14:21:29 +0530
From:   Anand Moon <linux.amoon@...il.com>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic@...ts.infradead.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        "open list:COMMON CLK FRAMEWORK" <linux-clk@...r.kernel.org>
Subject: Re: [PATCHv1 3/3] clk: meson: g12a: set cpu clock divider flags too CLK_IS_CRITICAL

Hi Jerome,

Thanks for your review comments.

On Mon, 17 Feb 2020 at 13:32, Jerome Brunet <jbrunet@...libre.com> wrote:
>
>
> On Sun 16 Feb 2020 at 18:34, Anand Moon <linux.amoon@...il.com> wrote:
>
> > Odroid N2 would fail to boot using microSD unless we set
> > cpu freq clk divider flags to CLK_IS_CRITICAL to avoid stalling of
> > cpu when booting, most likely because of PWM module linked to
>
> Where did you see a PWM ?
>
> > the CPU for DVFS is getting disabled in between the late_init call,
>
> between the late_init call and what ?
>
> > so gaiting the clock source shuts down the power to the codes.
>
> what code ?
>
> > Setting clk divider flags to CLK_IS_CRITICAL help resolve the issue.
> >
> > Cc: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> > Cc: Jerome Brunet <jbrunet@...libre.com>
> > Cc: Neil Armstrong <narmstrong@...libre.com>
> > Suggested-by: Neil Armstrong <narmstrong@...libre.com>
> > Signed-off-by: Anand Moon <linux.amoon@...il.com>
> > ---
> >
> > Following Neil's suggestion, I have prepared this patch.
> > https://patchwork.kernel.org/patch/11177441/#22964889
> > ---
> >  drivers/clk/meson/g12a.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/clk/meson/g12a.c b/drivers/clk/meson/g12a.c
> > index d2760a021301..accae3695fe5 100644
> > --- a/drivers/clk/meson/g12a.c
> > +++ b/drivers/clk/meson/g12a.c
> > @@ -283,6 +283,7 @@ static struct clk_fixed_factor g12a_fclk_div2_div = {
> >               .ops = &clk_fixed_factor_ops,
> >               .parent_hws = (const struct clk_hw *[]) { &g12a_fixed_pll.hw },
> >               .num_parents = 1,
> > +             .flags = CLK_IS_CRITICAL,
>
> This makes no sense for because:
> * This clock cannot gate and none of its parents can either. IOW, the
> output of this clock is never disabled.
> * I cannot guess the relation between fdiv2 and the commit description
>
> >       },
> >  };
> >
> > @@ -681,7 +682,7 @@ static struct clk_regmap g12b_cpub_clk = {
> >                       &g12a_sys_pll.hw
> >               },
> >               .num_parents = 2,
> > -             .flags = CLK_SET_RATE_PARENT,
> > +             .flags = CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
>
> Why not. Neil what do you think of this ?
> If nothing is claiming this clock and enabling it then I suppose it
> could make sense.
>
>
> >       },
> >  };
>

Sorry for the noise, I should not have send this patch in first place.

-Anand