Date:   Fri, 9 Dec 2022 12:29:04 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Hans de Goede <hdegoede@...hat.com>, <wsa@...nel.org>,
        <jarkko.nikula@...ux.intel.com>,
        <andriy.shevchenko@...ux.intel.com>,
        <mika.westerberg@...ux.intel.com>, <jsd@...ihalf.com>
CC:     <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH] i2c: designware: Fix unbalanced suspended flag

On 9/12/22 12:15, Hans de Goede wrote:
> Hi Richard,
> 
> On 12/9/22 12:40, Richard Fitzgerald wrote:
>> Ensure that i2c_mark_adapter_suspended() is always balanced by a call to
>> i2c_mark_adapter_resumed().
>>
>> Don't set DPM_FLAG_MAY_SKIP_RESUME to skip system early_resume stage if the
>> driver was runtime-suspended. Instead, always call dw_i2c_plat_resume() and
>> use pm_runtime_suspended() to determine whether we need to power up the
>> hardware.
>>
>> 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")
> 
> It is not entirely clear to me where the unbalance you claim to see comes
> from? When runtime-suspended SMART_SUSPEND should keep it suspended at which point
> the system suspend callback will never run ?

system suspend callback is called, which calls
i2c_mark_adapter_suspended().

system resume is NOT called so i2c_mark_adapter_resumed() is NOT called.

A subsequent audio playback using an I2C audio amp then does a
runtime resume but the amp driver then gets a "Transfer while suspended"
error when it tried to access the part over I2C during its own
runtime resume.

Tested on Aaeon UpXstreme WHL (Intel Whiskylake chipset)

Looking in __device_suspend_late() (drivers/base/power/main.c) there
are cases which will skip the SMART_SUSPEND check.

> 
> Are you sure that you are not maybe seeing a suspend/resume ordering issue?
> 
> Did you add printk messages to the suspend/resume callbacks of
> i2c-designware-platdrv.c which show the system suspend callback
> being called but not the system resume one ?
> 

Yes, that's what I did.
system suspend callback is called. System resume callback isn't.

> I guess that is possible with DPM_FLAG_MAY_SKIP_RESUME, but
> since we also use SMART_SUSPEND I would expect the system-suspend
> callback to also always be skipped for runtime-suspended controllers.
> 
> 
> 
> 
> 
> 
> 
>> ---
>> Apologies if you get this message multiple times. I'm having trouble
>> with my SMTP server.
>> ---
>>   drivers/i2c/busses/i2c-designware-platdrv.c | 10 +++++-----
>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
>> index ba043b547393..d805b8c7e797 100644
>> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
>> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
>> @@ -351,13 +351,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>>   
>>   	if (dev->flags & ACCESS_NO_IRQ_SUSPEND) {
>>   		dev_pm_set_driver_flags(&pdev->dev,
>> -					DPM_FLAG_SMART_PREPARE |
>> -					DPM_FLAG_MAY_SKIP_RESUME);
>> +					DPM_FLAG_SMART_PREPARE);
>>   	} else {
>>   		dev_pm_set_driver_flags(&pdev->dev,
>>   					DPM_FLAG_SMART_PREPARE |
>> -					DPM_FLAG_SMART_SUSPEND |
>> -					DPM_FLAG_MAY_SKIP_RESUME);
>> +					DPM_FLAG_SMART_SUSPEND);
>>   	}
>>   
>>   	device_enable_async_suspend(&pdev->dev);
>> @@ -475,7 +473,9 @@ static int __maybe_unused dw_i2c_plat_resume(struct device *dev)
>>   {
>>   	struct dw_i2c_dev *i_dev = dev_get_drvdata(dev);
>>   
>> -	dw_i2c_plat_runtime_resume(dev);
>> +	if (!pm_runtime_suspended(dev))
>> +		dw_i2c_plat_runtime_resume(dev);
>> +
> 
> I'm afraid that this is always going to run now, before this callback gets
> called drivers/base/power/main.c: device_resume_noirq() does:
> 
>          skip_resume = dev_pm_skip_resume(dev);
> 
>          if (skip_resume)
>                  pm_runtime_set_suspended(dev);
>          else if (dev_pm_skip_suspend(dev))
>                  pm_runtime_set_active(dev);
> 
> Where skip_resume now is false since you dropped the
> DPM_FLAG_MAY_SKIP_RESUME flag and dev_pm_skip_suspend(dev)
> will return true (see below) for runtime-suspended controllers,
> so they will be marked active here. and then your
> !pm_runtime_suspended(dev) will always be false.
> 
> Did you add a printk to both the if + else paths
> and have you ever seen the controller not get
> resumed with this test added ?
> 
> Regards,
> 
> Hans
> 
> 
> 
> 
> bool dev_pm_skip_suspend(struct device *dev)
> {
>          return dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) &&
>                  pm_runtime_status_suspended(dev);
> }
> 
> 
> 
> 
>>   	i2c_mark_adapter_resumed(&i_dev->adapter);
>>   
>>   	return 0;
> 

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