linux-kernel - Re: platform/i2c busses: pm runtime and system sleep

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Date:	Fri, 18 Feb 2011 10:05:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Rabin Vincent <rabin@....in>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	<linux-pm@...ts.linux-foundation.org>, <linux-i2c@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	<khilman@...com>, <magnus.damm@...il.com>
Subject: Re: platform/i2c busses: pm runtime and system sleep

On Fri, 18 Feb 2011, Rabin Vincent wrote:

> How about something like the below?  If we have something like this, we
> can just switch platform to GENERIC_PM_OPS and add the
> pm_runtime_want_interaction() (or something better named)

Yes, please find a better name!  Maybe something starting with 
"generic_" to indicate that this applies only to devices using the 
GENERIC_PM_OPS.

>  call to the
> i2c and spi drivers using runtime PM.

> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 42615b4..2b8a099 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1069,6 +1069,30 @@ void pm_runtime_allow(struct device *dev)
>  EXPORT_SYMBOL_GPL(pm_runtime_allow);
> 
>  /**
> + * pm_runtime_want_interaction - Enable interaction between system sleep
> + *				 and runtime PM callbacks at the bus/subsystem
> + *				 level.
> + * @dev: Device to handle
> + *
> + * Set the power.want_interaction flage, which tells the generic PM subsystem
> + * ops that the following actions should be done during system suspend/resume:
> + *
> + * - If the device has been runtime suspended, the driver's
> + *   suspend() handler will not be invoked.
> + *
> + * - If the device has a resume() pm callback, and the resume()
> + *   callback returns success on system resume, the device's
> + *   runtime PM status will be set to active.
> + */

This last part is normally true for all devices.  If you don't want it 
to hold when want_interaction isn't set, you should add a good 
explanation to sections 6 and 7 in Documentation/power/runtime.txt.

> +void pm_runtime_want_interaction(struct device *dev)
> +{
> +	spin_lock_irq(&dev->power.lock);
> +	dev->power.want_interaction = 1;
> +	spin_unlock_irq(&dev->power.lock);
> +}
> +EXPORT_SYMBOL_GPL(pm_runtime_want_interaction);
> +
> +/**
>   * pm_runtime_no_callbacks - Ignore run-time PM callbacks for a device.
>   * @dev: Device to handle.
>   *

Don't forget that you also need to describe these things in 
Documentation/power/runtime.txt.

Alan Stern

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