linux-kernel - Re: [PATCH v8 10/18] clk: tegra: Initialize PLL_X before CCLK

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Date:	Fri, 10 Apr 2015 14:08:32 -0700
From:	Michael Turquette <mturquette@...aro.org>
To:	Mikko Perttunen <mikko.perttunen@...si.fi>, swarren@...dotorg.org,
	thierry.reding@...il.com, gnurou@...il.com,
	pdeschrijver@...dia.com, rjw@...ysocki.net, viresh.kumar@...aro.org
Cc:	pwalmsley@...dia.com, vinceh@...dia.com, pgaikwad@...dia.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	tuomas.tynkkynen@....fi,
	"Mikko Perttunen" <mikko.perttunen@...si.fi>
Subject: Re: [PATCH v8 10/18] clk: tegra: Initialize PLL_X before CCLK_G to ensure it
 has a parent

Quoting Mikko Perttunen (2015-03-01 04:44:33)
> This patch moves the initialization of PLL_X to be slightly before
> that of CCLK_G. This ensures that at boot, CCLK_G will immediately
> have a parent and the common clock framework can determine its
> clock rate correctly.
> 
> Without this patch, calling clk_put on CCLK_G could cause the CCF
> to set its rate to zero, hanging the system.

Hi Mikko,

Patch looks fine to me but I wanted to get more info on the behavior you
mentioned above about clk_put. Is there some special circumstance that
causes this for you? Why does calling clk_put adjust the rate of your
clock?

Thanks,
Mike

> 
> Signed-off-by: Mikko Perttunen <mikko.perttunen@...si.fi>
> ---
> v8:
> - Added
> 
>  drivers/clk/tegra/clk-tegra-super-gen4.c | 46 ++++++++++++++++++--------------
>  1 file changed, 26 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/clk/tegra/clk-tegra-super-gen4.c b/drivers/clk/tegra/clk-tegra-super-gen4.c
> index f1f4410..c5ea9ee 100644
> --- a/drivers/clk/tegra/clk-tegra-super-gen4.c
> +++ b/drivers/clk/tegra/clk-tegra-super-gen4.c
> @@ -104,6 +104,32 @@ void __init tegra_super_clk_gen4_init(void __iomem *clk_base,
>         struct clk *clk;
>         struct clk **dt_clk;
>  
> +       /*
> +        * Register PLL_X first so that CCLK_G has a parent at registration
> +        * time. This ensures that the common clock framework knows CCLK_G's
> +        * rate.
> +        */
> +
> +#if defined(CONFIG_ARCH_TEGRA_114_SOC) || defined(CONFIG_ARCH_TEGRA_124_SOC)
> +       /* PLLX */
> +       dt_clk = tegra_lookup_dt_id(tegra_clk_pll_x, tegra_clks);
> +       if (!dt_clk)
> +               return;
> +
> +       clk = tegra_clk_register_pllxc("pll_x", "pll_ref", clk_base,
> +                       pmc_base, CLK_IGNORE_UNUSED, params, NULL);
> +       *dt_clk = clk;
> +
> +       /* PLLX_OUT0 */
> +
> +       dt_clk = tegra_lookup_dt_id(tegra_clk_pll_x_out0, tegra_clks);
> +       if (!dt_clk)
> +               return;
> +       clk = clk_register_fixed_factor(NULL, "pll_x_out0", "pll_x",
> +                                       CLK_SET_RATE_PARENT, 1, 2);
> +       *dt_clk = clk;
> +#endif
> +
>         /* CCLKG */
>         dt_clk = tegra_lookup_dt_id(tegra_clk_cclk_g, tegra_clks);
>         if (dt_clk) {
> @@ -127,25 +153,5 @@ void __init tegra_super_clk_gen4_init(void __iomem *clk_base,
>         }
>  
>         tegra_sclk_init(clk_base, tegra_clks);
> -
> -#if defined(CONFIG_ARCH_TEGRA_114_SOC) || defined(CONFIG_ARCH_TEGRA_124_SOC)
> -       /* PLLX */
> -       dt_clk = tegra_lookup_dt_id(tegra_clk_pll_x, tegra_clks);
> -       if (!dt_clk)
> -               return;
> -
> -       clk = tegra_clk_register_pllxc("pll_x", "pll_ref", clk_base,
> -                       pmc_base, CLK_IGNORE_UNUSED, params, NULL);
> -       *dt_clk = clk;
> -
> -       /* PLLX_OUT0 */
> -
> -       dt_clk = tegra_lookup_dt_id(tegra_clk_pll_x_out0, tegra_clks);
> -       if (!dt_clk)
> -               return;
> -       clk = clk_register_fixed_factor(NULL, "pll_x_out0", "pll_x",
> -                                       CLK_SET_RATE_PARENT, 1, 2);
> -       *dt_clk = clk;
> -#endif
>  }
>  
> -- 
> 2.3.0
> 
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