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

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Message-ID: <1jmu9hzlo2.fsf@starbuckisacylon.baylibre.com>
Date:   Mon, 17 Feb 2020 09:02:21 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Anand Moon <linux.amoon@...il.com>,
        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>
Cc:     Kevin Hilman <khilman@...libre.com>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCHv1 3/3] clk: meson: g12a: set cpu clock divider flags too CLK_IS_CRITICAL


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.


>  	},
>  };