linux-kernel - Re: [PATCH] apds9802als: add runtime PM support

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Message-ID: <Pine.LNX.4.44L0.1010271010170.1650-100000@iolanthe.rowland.org>
Date:	Wed, 27 Oct 2010 10:13:53 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Hong Liu <hong.liu@...el.com>
cc:	Alan Cox <alan@...ux.intel.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH] apds9802als: add runtime PM support

On Wed, 27 Oct 2010, Hong Liu wrote:

> In apds9802als_resume, I just want to power up the device, do some
> configuration, and then runtime_suspend the device.

Then you should change the function the way I suggested.  The PM core
will automatically do a runtime suspend after the system has fully
woken up.

> We don't have runtime_idle() implemented, the driver exported sysfs
> entries to user space for data reading, and we do runtime_resume,
> measaure data, runtime_suspend in the read/write funciton of those sysfs
> entries. This is why I want to put the device into runtime suspend
> manually whenever possible.

Your approach will not work.  You _must_ define runtime_idle() if you 
want your driver to suspend correctly.  It doesn't have to be 
complicated; just make it call pm_runtime_suspend().

...

> We don't have runtime_idle() implemented, so I have to manually put the
> device into runtime suspend.

The problem is that the device can be runtime-resumed by code other 
than your own, and that other code will not always do a runtime-suspend 
afterward -- it will do a runtime-idle.  That's why you need to define 
a runtime_idle() callback.

Alan Stern

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