linux-kernel - Re: [PATCH v4] clk: tegra: pll: Improve PLLM enable-state detection

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Message-ID: <997361b8-4466-cdf0-beeb-eedcbeb48597@nvidia.com>
Date:   Fri, 17 Jul 2020 17:55:38 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
CC:     <linux-tegra@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] clk: tegra: pll: Improve PLLM enable-state detection


On 09/07/2020 18:20, Dmitry Osipenko wrote:
> Power Management Controller (PMC) can override the PLLM clock settings,
> including the enable-state. Although PMC could only act as a second level
> gate, meaning that PLLM needs to be enabled by the Clock and Reset
> Controller (CaR) anyways if we want it to be enabled. Hence, when PLLM is
> overridden by PMC, it needs to be enabled by CaR and ungated by PMC in
> order to be functional. Please note that this patch doesn't fix any known
> problem, and thus, it's merely a minor improvement.
> 
> Link: https://lore.kernel.org/linux-arm-kernel/20191210120909.GA2703785@ulmo/T/
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
> 
> Changelog:
> 
> v4: - Renamed pllm_pmc_clk_enabled() to pllm_clk_is_gated_by_pmc() as
>       it was suggested by Jon Hunter in the review comment to v3.
> 
> v3: - Dropped unintended code change that was accidentally added to v2.
> 
> v2: - Added clarifying comment to the code.
> 
>     - Prettified the code.
> 
>  drivers/clk/tegra/clk-pll.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/clk/tegra/clk-pll.c b/drivers/clk/tegra/clk-pll.c
> index b2d39a66f0fa..ff13b371e176 100644
> --- a/drivers/clk/tegra/clk-pll.c
> +++ b/drivers/clk/tegra/clk-pll.c
> @@ -327,16 +327,26 @@ int tegra_pll_wait_for_lock(struct tegra_clk_pll *pll)
>  	return clk_pll_wait_for_lock(pll);
>  }
>  
> +static bool pllm_clk_is_gated_by_pmc(struct tegra_clk_pll *pll)
> +{
> +	u32 val = readl_relaxed(pll->pmc + PMC_PLLP_WB0_OVERRIDE);
> +
> +	return (val & PMC_PLLP_WB0_OVERRIDE_PLLM_OVERRIDE) &&
> +	      !(val & PMC_PLLP_WB0_OVERRIDE_PLLM_ENABLE);
> +}
> +
>  static int clk_pll_is_enabled(struct clk_hw *hw)
>  {
>  	struct tegra_clk_pll *pll = to_clk_pll(hw);
>  	u32 val;
>  
> -	if (pll->params->flags & TEGRA_PLLM) {
> -		val = readl_relaxed(pll->pmc + PMC_PLLP_WB0_OVERRIDE);
> -		if (val & PMC_PLLP_WB0_OVERRIDE_PLLM_OVERRIDE)
> -			return val & PMC_PLLP_WB0_OVERRIDE_PLLM_ENABLE ? 1 : 0;
> -	}
> +	/*
> +	 * Power Management Controller (PMC) can override the PLLM clock
> +	 * settings, including the enable-state. The PLLM is enabled when
> +	 * PLLM's CaR state is ON and when PLLM isn't gated by PMC.
> +	 */
> +	if ((pll->params->flags & TEGRA_PLLM) && pllm_clk_is_gated_by_pmc(pll))
> +		return 0;
>  
>  	val = pll_readl_base(pll);
>  
> 

I have tested this on Jetson TK1 using u-boot to verify the behaviour
and it does indeed work as described here. I have also ran it through
the automated testing we have for Tegra and see no immediate issue.
Therefore ...

Reviewed-by: Jon Hunter <jonathanh@...dia.com>
Tested-by: Jon Hunter <jonathanh@...dia.com>

Thanks!
Jon

-- 
nvpublic