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

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Date:	Tue, 26 Oct 2010 14:05:17 +0800
From:	Hong Liu <hong.liu@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
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 Fri, 2010-10-22 at 02:34 +0800, Alan Stern wrote:
> On Fri, 15 Oct 2010, Alan Cox wrote:
> 
> > From: Hong Liu <hong.liu@...el.com>
> > 
> > 
> >     Update the driver for the needed runtime power features. Remove the old
> >     user controlled power functions.
> > 
> >     Signed-off-by: Hong Liu <hong.liu@...el.com>
> >     Signed-off-by: Alan Cox <alan@...ux.intel.com>
> 
> > diff --git a/drivers/misc/apds9802als.c b/drivers/misc/apds9802als.c
> > index fbe4960..15f9436 100644
> > --- a/drivers/misc/apds9802als.c
> > +++ b/drivers/misc/apds9802als.c
> 
> > @@ -265,13 +274,34 @@ static int apds9802als_suspend(struct i2c_client *client, pm_message_t mesg)
> >  
> >  static int apds9802als_resume(struct i2c_client *client)
> >  {
> > -	struct als_data *data = i2c_get_clientdata(client);
> > +	als_set_default_config(client);
> > +
> > +	pm_runtime_get(&client->dev);
> > +	pm_runtime_put(&client->dev);
> > +	return 0;
> > +}
> 

Hi, Alan

Thanks for your review.

> This almost certainly does not do what you think.
> 
> pm_runtime_get() will increment the device's usage count and queue an 
> asynchronous resume request.  However, since the PM workqueue is frozen 
> during system sleep transitions, the device will remain suspended.
> 
> The pm_runtime_put() will decrement the usage count again, but since
> there is already an async resume on the queue it will not queue an
> async suspend.  The final result will be that when tasks are unfrozen,
> the device will finally be resumed -- long after it should have been.
> 
> It looks like what you want to do here is simply call
> apds9802als_runtime_resume() directly.  

You mean apds9802als_runtime_suspend()? I want to put the device into
runtime suspended state, can I just call pm_runtime_suspend() directly?

> And according to the advice in
> Documentation/power/runtime_pm.txt section 6, you should also call
> 
> 	pm_runtime_disable(dev);
> 	pm_runtime_set_active(dev);
> 	pm_runtime_enable(dev);
> 
> You probably also do not want the asynchronous calls to 
> pm_runtime_get() and pm_runtime_put() in apds9802als_probe().  A more 
> common sequence is:
> 
> 	pm_runtime_set_active(dev);
> 	pm_runtime_enable(dev);

I want to put the device into runtime suspend state after probe, so
pm_runtime_suspend() after these two calls is OK?

Thanks,
Hong

> 
> Alan Stern
> 


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