linux-kernel - Re: [PATCH v3] clk: tegra: pll: Improve PLLM enable-state detection

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Date:   Thu, 9 Jul 2020 10:49:28 +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 v3] clk: tegra: pll: Improve PLLM enable-state detection


On 08/07/2020 08:54, 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:
> 
> 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..37cfcd6836c9 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_pmc_clk_enabled(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);
> +}
> +


I am not sure that the name of the above function really reflects what
it is doing. If it was enabled, isn't it the AND of these bits?

Futhermore, what we really want to know is if the override is enabled,
but the PMC PLLM enable is not set. In other words, the PMC is gating
the clock. So maybe we should have a function that is called something
like pllm_clk_is_gated_by_pmc().

Jon

-- 
nvpublic