linux-kernel - Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.

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Date:	Fri, 20 Jun 2014 14:34:14 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Allen Yu <alleny@...dia.com>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-pm\@vger.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.

Alan Stern <stern@...land.harvard.edu> writes:

> On Fri, 20 Jun 2014, Rafael J. Wysocki wrote:
>
>> > For a general device, the fact that dev->power.is_suspended is set
>> > means the device _has_ been powered down.  Even though the
>> > runtime_status may not have changed, the PM core has to assume the
>> > device is not available for use.
>> 
>> This seems to go a bit too far.  What power.is_suspended actually means is
>> that __device_suspend() has run for the device successfully.  What the
>> implications of that are depends on the bus type (or subsystem in general)
>> and device driver.
>> 
>> > While your I2C devices may be useable even after the ->suspend callback
>> > returns, for most devices this isn't true.  So we shouldn't allow
>> > rpm_resume() to return imediately when is_suspended is set.
>> 
>> I can agree with that.
>
> We really do need to decide more precisely how runtime PM and system PM 
> will interact.  

Yes!

> Should ->runtime_resume callbacks be allowed after ->suspend has
> returned?

Abolutely.

> Kevin has stated that some devices do need this ability.  But most
> don't.  

Does it matter if most don't?  As long a some do, we need to support
this.  It may not be "most" devices, but on the (mostly embedded) SoCs I
work on, the devices that do need this tend to be rather crucial core
devices that are used during the PM of other devices (e.g. I2C, SPI,
GPIOs, etc. etc.)

> The PM core needs to handle these conflicting requirements
> somehow.

I agree.  We've gone back and forth a few times on the various
interactions between system PM and runtime PM over the years but it
seems there are still things to clarify.

Kevin
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