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

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Date:	Mon, 25 Apr 2016 12:07:15 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Jisheng Zhang <jszhang@...vell.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

On Fri, 2016-04-22 at 16:59 +0300, Jarkko Nikula wrote:
> 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?

Now it looks like two fixes in one patch. From the commit message I
didn't get the relation between change runtime PM call (one to the
other) and clock (un)preparation.


-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy