linux-kernel - Re: [PATCH v2 1/1] clk: samsung: exynos850: Register clocks early

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Message-ID: <fcc939e6-50b4-1847-c738-db940d0c5bd4@samsung.com>
Date:   Sat, 20 Nov 2021 13:49:31 +0100
From:   Sylwester Nawrocki <s.nawrocki@...sung.com>
To:     Sam Protsenko <semen.protsenko@...aro.org>
Cc:     Sumit Semwal <sumit.semwal@...aro.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Paweł Chmiel <pawel.mikolaj.chmiel@...il.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH v2 1/1] clk: samsung: exynos850: Register clocks early

On 25.10.2021 18:12, Sam Protsenko wrote:
> Some clocks must be registered before init calls. For example MCT clock
> (from CMU_PERI) is needed for MCT timer driver, which is registered
> with TIMER_OF_DECLARE(). By the time we get to core_initcall() used for
> clk-exynos850 platform driver init, it's already too late. Inability to
> get "mct" clock in MCT driver leads to kernel panic, as functions
> registered with *_OF_DECLARE() can't do deferred calls. MCT timer driver
> can't be fixed either, as it's acting as a clock source and it's
> essential to register it in start_kernel() -> time_init().
> 
> Let's register CMU_PERI clocks early, using CLK_OF_DECLARE_DRIVER(), and
> do all stuff relying on "struct dev" object (like runtime PM and
> enabling bus clock) later in platform driver probe. Basically
> CLK_OF_DECLARE_DRIVER() matches CMU compatible, but clears OF_POPULATED
> flag, which allows the same device to be matched again later.

> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>

>  drivers/clk/samsung/clk-exynos850.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/samsung/clk-exynos850.c b/drivers/clk/samsung/clk-exynos850.c
> index 95e373d17b42..ecffa5c7a081 100644
> --- a/drivers/clk/samsung/clk-exynos850.c
> +++ b/drivers/clk/samsung/clk-exynos850.c
> @@ -753,6 +753,15 @@ static const struct samsung_cmu_info peri_cmu_info __initconst = {
>  	.clk_name		= "dout_peri_bus",
>  };
>  
> +static void __init exynos850_cmu_peri_init(struct device_node *np)
> +{
> +	exynos850_init_clocks(np, peri_clk_regs, ARRAY_SIZE(peri_clk_regs));
> +	samsung_cmu_register_one(np, &peri_cmu_info);
> +}
> +
> +CLK_OF_DECLARE_DRIVER(exynos850_cmu_peri, "samsung,exynos850-cmu-peri",
> +		      exynos850_cmu_peri_init);
> +
>  /* ---- CMU_CORE ------------------------------------------------------------ */
>  
>  /* Register Offset definitions for CMU_CORE (0x12000000) */
> @@ -920,8 +929,12 @@ static int __init exynos850_cmu_probe(struct platform_device *pdev)
>  	struct device_node *np = dev->of_node;
>  
>  	info = of_device_get_match_data(dev);
> -	exynos850_init_clocks(np, info->clk_regs, info->nr_clk_regs);
> -	samsung_cmu_register_one(np, info);
> +
> +	/* Early clocks are already registered using CLK_OF_DECLARE_DRIVER() */
> +	if (info != &peri_cmu_info) {
> +		exynos850_init_clocks(np, info->clk_regs, info->nr_clk_regs);
> +		samsung_cmu_register_one(np, info);
> +	}

Don't you also need to register early CMU_TOP, which provides clocks
for CMU_PERI? I'm afraid it might not work properly when you register 
CMU_PERI clocks early and only later in probe() you enable parent clock
required for the already registered clocks to be usable.
How about registering also CMU_TOP early and enabling parent clock
also in OF_CLK_DECLARE init callback, i.e. using either OF_CLK_DECLARE
or platform driver for a CMU? 

-- 
Regards,
Sylwester