linux-kernel - Re: [PATCH v2] i2c: designware: Fix unbalanced suspended flag

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Message-ID: <8cf30cb2-6dec-b21b-ba15-f21490546426@redhat.com>
Date:   Wed, 14 Dec 2022 12:28:49 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>,
        jarkko.nikula@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
        mika.westerberg@...ux.intel.com, jsd@...ihalf.com, wsa@...nel.org
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com
Subject: Re: [PATCH v2] i2c: designware: Fix unbalanced suspended flag

Hi Richard,

On 12/13/22 15:45, Richard Fitzgerald wrote:
> Ensure that i2c_mark_adapter_suspended() is always balanced by a call to
> i2c_mark_adapter_resumed().
> 
> dw_i2c_plat_resume() must always be called, so that
> i2c_mark_adapter_resumed() is called. This is not compatible with
> DPM_FLAG_MAY_SKIP_RESUME.
> 
> The pairing of pm_runtime_force_suspend() and pm_runtime_force_resume()
> can replace this. If nothing is using the driver, and it is not currently
> suspended, it will be put into runtime-suspend and will be left in
> runtime-suspend during the system resume.
> 
> pm_runtime_force_suspend() is not compatible with DPM_FLAG_SMART_SUSPEND
> so this must also be removed. DPM_FLAG_SMART_SUSPEND will set the device
> back to pm_runtime_active() during resume_noirq if it cannot skip resume.
> This would lead to the inconsistent state where the driver runtime_suspend
> has been called (by force_suspend()) but it is marked active (by PM core).
> 
> The unbalanced suspended flag was introduced by
> commit c57813b8b288 ("i2c: designware: Lock the adapter while setting the
> suspended flag")
> 
> Before that commit, the system and runtime PM used the same functions. The
> DPM_FLAG_MAY_SKIP_RESUME was used to skip the system resume if the driver
> had been in runtime-suspend. If system resume was skipped, the suspended
> flag would be cleared by the next runtime resume. The check of the
> suspended flag was _after_ the call to pm_runtime_get_sync() in
> i2c_dw_xfer(). So either a system resume or a runtime resume would clear
> the flag before it was checked.
> 
> Having introduced the unbalanced suspended flag with that commit, a further
> commit 80704a84a9f8 ("i2c: designware: Use the
> i2c_mark_adapter_suspended/resumed() helpers")
> 
> changed from using a local suspended flag to using the
> i2c_mark_adapter_suspended/resumed() functions. These use a flag that is
> checked by I2C core code before issuing the transfer to the bus driver, so
> there was no opportunity for the bus driver to runtime resume itself before
> the flag check.
> 
> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> Fixes: c57813b8b288 ("i2c: designware: Lock the adapter while setting the suspended flag")

Thank you. I like the new approach in this version.

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans



> ---
>  drivers/i2c/busses/i2c-designware-platdrv.c | 26 ++++++++++-----------
>  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> index ba043b547393..590503e56bd0 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -349,17 +349,7 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>  	adap->dev.of_node = pdev->dev.of_node;
>  	adap->nr = -1;
>  
> -	if (dev->flags & ACCESS_NO_IRQ_SUSPEND) {
> -		dev_pm_set_driver_flags(&pdev->dev,
> -					DPM_FLAG_SMART_PREPARE |
> -					DPM_FLAG_MAY_SKIP_RESUME);
> -	} else {
> -		dev_pm_set_driver_flags(&pdev->dev,
> -					DPM_FLAG_SMART_PREPARE |
> -					DPM_FLAG_SMART_SUSPEND |
> -					DPM_FLAG_MAY_SKIP_RESUME);
> -	}
> -
> +	dev_pm_set_driver_flags(&pdev->dev, DPM_FLAG_SMART_PREPARE);
>  	device_enable_async_suspend(&pdev->dev);
>  
>  	/* The code below assumes runtime PM to be disabled. */
> @@ -453,10 +443,15 @@ static int dw_i2c_plat_runtime_suspend(struct device *dev)
>  static int __maybe_unused dw_i2c_plat_suspend(struct device *dev)
>  {
>  	struct dw_i2c_dev *i_dev = dev_get_drvdata(dev);
> +	int ret;
> +
> +	ret = pm_runtime_force_suspend(dev);
> +	if (ret)
> +		return ret;
>  
>  	i2c_mark_adapter_suspended(&i_dev->adapter);
>  
> -	return dw_i2c_plat_runtime_suspend(dev);
> +	return 0;
>  }
>  
>  static int dw_i2c_plat_runtime_resume(struct device *dev)
> @@ -474,8 +469,13 @@ static int dw_i2c_plat_runtime_resume(struct device *dev)
>  static int __maybe_unused dw_i2c_plat_resume(struct device *dev)
>  {
>  	struct dw_i2c_dev *i_dev = dev_get_drvdata(dev);
> +	int ret;
> +
> +	/* Resume if pm_runtime_force_suspend() suspended. */
> +	ret = pm_runtime_force_resume(dev);
> +	if (ret)
> +		return ret;
>  
> -	dw_i2c_plat_runtime_resume(dev);
>  	i2c_mark_adapter_resumed(&i_dev->adapter);
>  
>  	return 0;