linux-kernel - Re: [PATCH v1 3/3] i2c: tegra: Fix suspending in active runtime PM state

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Message-ID: <ae96db3a-0854-6e80-0469-e5fa6fd7bb8e@gmail.com>
Date:   Fri, 13 Dec 2019 17:29:42 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mikko Perttunen <cyndis@...si.fi>
Subject: Re: [PATCH v1 3/3] i2c: tegra: Fix suspending in active runtime PM
 state

13.12.2019 02:34, Dmitry Osipenko пишет:
> I noticed that sometime I2C clock is kept enabled during suspend-resume.
> This happens because runtime PM defers dynamic suspension and thus it may
> happen that runtime PM is in active state when system enters into suspend.
> In particular I2C controller that is used for CPU's DVFS is often kept ON
> during suspend because CPU's voltage scaling happens quite often.
> 
> Note: we marked runtime PM as IRQ-safe during the driver's probe in the
> "Support atomic transfers" patch, thus it's okay to enforce runtime PM
> suspend/resume in the NOIRQ phase which is used for the system-level
> suspend/resume of the driver.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/i2c/busses/i2c-tegra.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
> index b3ecdd87e91f..d309a314f4d6 100644
> --- a/drivers/i2c/busses/i2c-tegra.c
> +++ b/drivers/i2c/busses/i2c-tegra.c
> @@ -1790,9 +1790,14 @@ static int tegra_i2c_remove(struct platform_device *pdev)
>  static int __maybe_unused tegra_i2c_suspend(struct device *dev)
>  {
>  	struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
> +	int err;
>  
>  	i2c_mark_adapter_suspended(&i2c_dev->adapter);

I'm now in a doubt that it is correct to use NOIRQ level at all for the
suspend because i2c_mark_adapter_suspended() uses mutex, thus I'm
wondering what will happen if there is an asynchronous transfer
happening during suspend..

The i2c_mark_adapter_suspended() will try to block and will never return?

> +	err = pm_runtime_force_suspend(dev);
> +	if (err < 0)
> +		return err;
> +
>  	return 0;
>  }
>  
> @@ -1813,6 +1818,10 @@ static int __maybe_unused tegra_i2c_resume(struct device *dev)
>  	if (err)
>  		return err;
>  
> +	err = pm_runtime_force_resume(dev);
> +	if (err < 0)
> +		return err;
> +
>  	i2c_mark_adapter_resumed(&i2c_dev->adapter);
>  
>  	return 0;
>