linux-kernel - Re: [PATCH v4] i2c: designware-platdrv: fix unbalanced clk enable and prepare

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Date:	Fri, 22 Apr 2016 16:59:31 +0300
From:	Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:	Jisheng Zhang <jszhang@...vell.com>,
	andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
	wsa@...-dreams.de
Cc:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4] i2c: designware-platdrv: fix unbalanced clk enable and
 prepare

Hi

On 04/22/2016 11:49 AM, Jisheng Zhang wrote:
> If i2c_dw_probe() fails, we should disable and unprepare the clock,
> otherwise the clock enable and prepare is left unbalanced.
>
> In dw_i2c_plat_remove(), we'd better to not rely on runtime PM to
> disable and unprepare the clock since CONFIG_PM may be disabled when
> configuring the kernel. So we explicitly disable and unprepare the
> clock in dw_i2c_plat_remove() rather than implicitly rely on
> pm_runtime_put_sync(). To keep the device usage count balanced, we
> call pm_runtime_put_noidle() to decrease the usage count.
>
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> ---
>   Since v3:
>    - use runtime PM rather than rpm in commit msg
>    - remove duplicated "(" in commit msg
>
>   Since v2:
>    - s/clk/clock
>    - describe why use pm_runtime_put_noidle()
>
>   Since v1:
>    - fix commit msg: "not rely on rpm" rather than "rely on rpm"
>    - call i2c_dw_plat_prepare_clk after pm_rumtime_disable()
>   drivers/i2c/busses/i2c-designware-platdrv.c | 16 ++++++++++------
>   1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> index d656657..a771781 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -253,8 +253,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>   	}
>
>   	r = i2c_dw_probe(dev);
> -	if (r && !dev->pm_runtime_disabled)
> -		pm_runtime_disable(&pdev->dev);
> +	if (r) {
> +		if (!dev->pm_runtime_disabled)
> +			pm_runtime_disable(&pdev->dev);
> +		i2c_dw_plat_prepare_clk(dev, false);
> +	}
>
>   	return r;
>   }
> @@ -264,15 +267,16 @@ static int dw_i2c_plat_remove(struct platform_device *pdev)
>   	struct dw_i2c_dev *dev = platform_get_drvdata(pdev);
>
>   	pm_runtime_get_sync(&pdev->dev);
> +	pm_runtime_dont_use_autosuspend(&pdev->dev);
> +	if (!dev->pm_runtime_disabled)
> +		pm_runtime_disable(&pdev->dev);
> +	pm_runtime_put_noidle(&pdev->dev);
>
>   	i2c_del_adapter(&dev->adapter);
>
>   	i2c_dw_disable(dev);
>
> -	pm_runtime_dont_use_autosuspend(&pdev->dev);
> -	pm_runtime_put_sync(&pdev->dev);
> -	if (!dev->pm_runtime_disabled)
> -		pm_runtime_disable(&pdev->dev);
> +	i2c_dw_plat_prepare_clk(dev, false);
>
This feels a bit an invasive change to me for unbalanced clock 
enable/disable and I noticed this changes semantics how 
drivers/acpi/acpi_lpss.c devices are shutdown when removing the driver. 
Although I didn't notice does it cause any regression.

Before patch:
1. drivers/base/dd.c: __device_release_driver()
    - pm_runtime_get_sync()
      -> acpi_device_set_power(D0)
         acpi_lpss_restore_ctx()
         dw_i2c_plat_resume()
2. dw_i2c_plat_remove()
    - pm_runtime_dont_use_autosuspend()
      pm_runtime_put_sync()
      -> dw_i2c_plat_suspend()
         acpi_lpss_save_ctx()
         acpi_device_set_power(D3)
3. __device_release_driver() continue
    - dev->pm_domain->dismiss(dev)
      -> acpi_lpss_dismiss() ... -> acpi_device_set_power(D3)

After patch:
1. drivers/base/dd.c: __device_release_driver()
  - pm_runtime_get_sync()
    -> acpi_device_set_power(D0)
       acpi_lpss_restore_ctx()
       dw_i2c_plat_resume()
2. dw_i2c_plat_remove()
    - pm_runtime_dont_use_autosuspend()
      pm_runtime_put_noidle()
      * no device suspending and acpi_lpss_save_ctx()
3. __device_release_driver() continue
    - dev->pm_domain->dismiss(dev)
    -> acpi_lpss_dismiss() ... -> acpi_device_set_power(D3)
      * powers down here

So after patch there is no acpi_lpss_save_ctx() call but I don't see 
does it cause any issue here. Maybe it's better to track clock only. 
What you think Andy?

-- 
Jarkko