linux-kernel - Re: [PATCH] clk: exynos5420: Keep aclk66

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Date:	Thu, 29 May 2014 15:29:04 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Doug Anderson <dianders@...omium.org>,
	"Tomasz Figa" <t.figa@...sung.com>,
	"Kukjin Kim" <kgene.kim@...sung.com>
Cc:	olof@...om.net, javier.martinez@...labora.co.uk,
	"Doug Anderson" <dianders@...omium.org>,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clk: exynos5420: Keep aclk66_peric enabled during boot

Quoting Doug Anderson (2014-05-29 14:21:36)
> Right now if you've got earlyprintk enabled on exynos5420-peach-pit
> then you'll get a hang on boot.  Here's why:
> 
> 1. The i2c-s3c2410 driver will probe at subsys_initcall.  It will
>    enable its clock and disable it.  This is the clock "i2c2".
> 2. The act of disabling "i2c2" will disable its parents.  In this case
>    the parent is "aclk66_peric".  There are no other children of
>    "aclk66_peric" officially enabled, so "aclk66_peric" will be turned
>    off (despite being CLK_IGNORE_UNUSED, but that's by design).
> 3. The next time you try to earlyprintk you'll do so without the UART
>    clock enabled.  That's because the UART clocks are also children of
>    "aclk66_peric".  You'll hang.
> 
> There's no good place to put a clock enable for earlyprintk, which is
> handled by a bunch of assembly code.  The best we can do is to handle
> this in the clock driver.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
>  drivers/clk/samsung/clk-exynos5420.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/clk/samsung/clk-exynos5420.c b/drivers/clk/samsung/clk-exynos5420.c
> index 9d7d7ee..1e586be 100644
> --- a/drivers/clk/samsung/clk-exynos5420.c
> +++ b/drivers/clk/samsung/clk-exynos5420.c
> @@ -1172,11 +1172,17 @@ static struct of_device_id ext_clk_match[] __initdata = {
>         { },
>  };
>  
> +/* Keep these clocks on until late_initcall */
> +static const char *boot_clocks[] __initconst = {
> +       "aclk66_peric",
> +};
> +
>  /* register exynos5420 clocks */
>  static void __init exynos5x_clk_init(struct device_node *np,
>                 enum exynos5x_soc soc)
>  {
>         struct samsung_clk_provider *ctx;
> +       int i;
>  
>         if (np) {
>                 reg_base = of_iomap(np, 0);
> @@ -1226,6 +1232,12 @@ static void __init exynos5x_clk_init(struct device_node *np,
>         }
>  
>         exynos5420_clk_sleep_init();
> +
> +       for (i = 0; i < ARRAY_SIZE(boot_clocks); i++) {
> +               struct clk *to_enable = __clk_lookup(boot_clocks[i]);

How about replacing __clk_lookup with clk_get? You can keep the struct
clk object hanging around for later...

> +
> +               clk_prepare_enable(to_enable);
> +       }
>  }
>  
>  static void __init exynos5420_clk_init(struct device_node *np)
> @@ -1239,3 +1251,15 @@ static void __init exynos5800_clk_init(struct device_node *np)
>         exynos5x_clk_init(np, EXYNOS5800);
>  }
>  CLK_OF_DECLARE(exynos5800_clk, "samsung,exynos5800-clock", exynos5800_clk_init);
> +
> +static int __init exynos5420_clk_late_init(void)
> +{
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(boot_clocks); i++) {
> +               struct clk *to_disable = __clk_lookup(boot_clocks[i]);
> +
> +               clk_disable_unprepare(to_disable);

And then release it here with a clk_put.

Regards,
Mike

> +       }
> +}
> +late_initcall(exynos5420_clk_late_init);
> -- 
> 1.9.1.423.g4596e3a
> 
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