linux-kernel - Re: [PATCH] PM / runtime: Document steps for device removal

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Date:	Tue, 15 Mar 2016 08:54:07 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Alan Stern <stern@...land.harvard.edu>,
	Krzysztof Kozlowski <krzk@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM / runtime: Document steps for device removal

On 13.03.2016 01:57, Alan Stern wrote:
> On Sat, 12 Mar 2016, Krzysztof Kozlowski wrote:
> 
>> Put a reminder that during device removal drivers should revert all PM
>> runtime changes from the probe. Also add a note that
>> pm_runtime_disable() won't wait for pending suspend requests if
>> autosuspend is not disabled before.
>>
>> Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
>> ---
>>  Documentation/power/runtime_pm.txt | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
>> index 7328cf85236c..c05e5a17a52d 100644
>> --- a/Documentation/power/runtime_pm.txt
>> +++ b/Documentation/power/runtime_pm.txt
>> @@ -410,7 +410,8 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
>>        field was previously zero, this prevents subsystem-level runtime PM
>>        callbacks from being run for the device), make sure that all of the
>>        pending runtime PM operations on the device are either completed or
>> -      canceled; returns 1 if there was a resume request pending and it was
>> +      canceled (although this depends on disabling autosuspend before
>> +      calling this); returns 1 if there was a resume request pending and it was
> 
> I don't agree with this change.  All pending operations really are
> either completed or cancelled, even if autosuspend is enabled.
> 
> Any strange behavior you saw after disabling runtime PM and then 
> enabling it again was caused by new operations being started after you 
> re-enabled runtime PM.

Hmmm, okay, I'll resend only with second part below.

Best regards,
Krzysztof

> 
>>        necessary to execute the subsystem-level resume callback for the device
>>        to satisfy that request, otherwise 0 is returned
>>  
>> @@ -586,6 +587,10 @@ drivers to make their ->remove() callbacks avoid races with runtime PM directly,
>>  but also it allows of more flexibility in the handling of devices during the
>>  removal of their drivers.
>>  
>> +Drivers in ->remove() callback should undo the runtime PM changes done
>> +in ->probe(). Usually this means calling pm_runtime_disable(),
>> +pm_runtime_dont_use_autosuspend() etc.
>> +
> 
> That's a good addition.
> 
>>  The user space can effectively disallow the driver of the device to power manage
>>  it at run time by changing the value of its /sys/devices/.../power/control
>>  attribute to "on", which causes pm_runtime_forbid() to be called.  In principle,
> 
> Alan Stern
> 
> 
>