linux-kernel - Re: [RFC v1 5/7] clk: meson: meson8b: mark the CPU clock as CLK_IS

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Date:   Thu, 15 Nov 2018 10:46:46 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org,
        narmstrong@...libre.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mturquette@...libre.com, sboyd@...nel.org
Subject: Re: [RFC v1 5/7] clk: meson: meson8b: mark the CPU clock as
 CLK_IS_CRITICAL

On Wed, 2018-11-14 at 23:57 +0100, Martin Blumenstingl wrote:
> We don't want the common clock framework to disable the "cpu_clk" if
> it's not used by any device. The cpufreq-dt driver does not enable the
> CPU clocks. However, even if it would we would still want the CPU clock
> to be enabled at all times because the CPU clock is also required even
> if we disable CPU frequency scaling on a specific board.
> 
> The reason why we want the CPU clock to be enabled is a clock further up
> in the tree:
> Since commit 6f888e7bc7bd58 ("clk: meson: clk-pll: add enable bit") the
> sys_pll can be disabled. However, since the CPU clock is derived from
> sys_pll we don't want sys_pll to get disabled. The common clock
> framework takes care of that for us by enabling all parent clocks of our
> CPU clock when we mark the CPU clock with CLK_IS_CRITICAL.
> 
> Until now this is not a problem yet because all clocks in the CPU
> clock's tree (including sys_pll) are read-only. However, once we allow
> modifications to the clocks in that tree we will need this.
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> ---
>  drivers/clk/meson/meson8b.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/meson/meson8b.c b/drivers/clk/meson/meson8b.c
> index 8a3c346e110d..d566dd5bc567 100644
> --- a/drivers/clk/meson/meson8b.c
> +++ b/drivers/clk/meson/meson8b.c
> @@ -646,7 +646,8 @@ static struct clk_regmap meson8b_cpu_clk = {
>  						  "cpu_scale_out_sel" },
>  		.num_parents = 2,
>  		.flags = (CLK_SET_RATE_PARENT |
> -			  CLK_SET_RATE_NO_REPARENT),
> +			  CLK_SET_RATE_NO_REPARENT |
> +			  CLK_IS_CRITICAL),
>  	},
>  };
>  

Acked-by: Jerome Brunet <jbrunet@...libre.com>