linux-kernel - Re: [PATCH v1] soc/tegra: pmc: Query PCLK clock rate at probe time

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Date:   Thu, 18 Jul 2019 10:45:31 +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>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] soc/tegra: pmc: Query PCLK clock rate at probe time


On 08/07/2019 00:08, Dmitry Osipenko wrote:
> The PCLK clock is running off SCLK, which is a critical clock that is
> very unlikely to randomly change its rate. It's also a bit clumsy (and
> apparently incorrect) to query the clock's rate with interrupts being
> disabled because clk_get_rate() takes a mutex and that's the case during
> suspend/cpuidle entering. Lastly, it's better to always fully reprogram
> PMC state because it's not obvious whether it could be changed after SC7.

I agree with the first part, but I would drop the last sentence because
I see no evidence of this. Maybe Peter can confirm.

> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/soc/tegra/pmc.c | 26 +++++++++++---------------
>  1 file changed, 11 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
> index 9f9c1c677cf4..532e0ada012b 100644
> --- a/drivers/soc/tegra/pmc.c
> +++ b/drivers/soc/tegra/pmc.c
> @@ -1433,6 +1433,7 @@ void tegra_pmc_set_suspend_mode(enum tegra_suspend_mode mode)
>  void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>  {
>  	unsigned long long rate = 0;
> +	u64 ticks;
>  	u32 value;
>  
>  	switch (mode) {
> @@ -1441,7 +1442,7 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>  		break;
>  
>  	case TEGRA_SUSPEND_LP2:
> -		rate = clk_get_rate(pmc->clk);
> +		rate = pmc->rate;

There is another call to clk_get_rate() that could be removed as well.

>  		break;
>  
>  	default:
> @@ -1451,26 +1452,20 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
>  	if (WARN_ON_ONCE(rate == 0))
>  		rate = 100000000;
>  
> -	if (rate != pmc->rate) {
> -		u64 ticks;
> -
> -		ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
> -		do_div(ticks, USEC_PER_SEC);
> -		tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
> -
> -		ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
> -		do_div(ticks, USEC_PER_SEC);
> -		tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
> +	ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
> +	do_div(ticks, USEC_PER_SEC);
> +	tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);

You could go a step further and update the cpu_good_time/cpu_off_time to
be ticks and calculated once during probe and recalculated if
tegra_pmc_set_suspend_mode is called. I am not sure why we really need
to pass mode to tegra_pmc_enter_suspend_mode() seeing as the mode is
stored in the pmc struct.

>  
> -		wmb();
> -
> -		pmc->rate = rate;
> -	}
> +	ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
> +	do_div(ticks, USEC_PER_SEC);
> +	tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
>  
>  	value = tegra_pmc_readl(pmc, PMC_CNTRL);
>  	value &= ~PMC_CNTRL_SIDE_EFFECT_LP0;
>  	value |= PMC_CNTRL_CPU_PWRREQ_OE;
>  	tegra_pmc_writel(pmc, value, PMC_CNTRL);
> +
> +	wmb();
>  }
>  #endif
>  
> @@ -2082,6 +2077,7 @@ static int tegra_pmc_probe(struct platform_device *pdev)
>  		pmc->clk = NULL;
>  	}
>  
> +	pmc->rate = clk_get_rate(pmc->clk);

You should check the value returned is not 0 here.

Cheers
Jon

-- 
nvpublic