linux-kernel - Re: [PATCH 1/4] PM / Wakeirq: Add minimal device wakeirq helper functions

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Date:	Mon, 9 Mar 2015 11:42:28 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tony Lindgren <tony@...mide.com>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Andreas Fenkart <afenkart@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>,
	Huiquan Zhong <huiquan.zhong@...el.com>,
	Kevin Hilman <khilman@...nel.org>, NeilBrown <neilb@...e.de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Nishanth Menon <nm@...com>,
	Peter Hurley <peter@...leysoftware.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 1/4] PM / Wakeirq: Add minimal device wakeirq helper
 functions

On Mon, 9 Mar 2015, Tony Lindgren wrote:

> > > > > Considering the above, should we add a new function something like
> > > > > pm_resume_complete() that does not need irq_safe set but does
> > > > > not return until the device has completed resume?
> > > > 
> > > > That doesn't make sense.  You're asking for a routine that is allowed
> > > > to sleep but can safely be called in interrupt context.
> > > 
> > > Oh it naturally would not work in irq context, it's for the bottom
> > > half again.
> > 
> > In other words, you're suggesting we add a function that runs in 
> > process context and doesn't return until the device is fully resumed?  
> > That's exactly what pm_runtime_resume does right now.
> 
> But doesn't it only wait for completion if the driver is marked with
> pm_runtime_irq_safe()?

Put it this way: pm_runtime_resume invokes a ->runtime_resume
callback routine (the subsystem's or the driver's or whichever), and it
assumes that if the routine returns 0 then the device has been resumed.  
It doesn't really _wait_ for anything; it just calls the callback
routine.

It behaves this way whether or not the irq_safe flag is set.  The only
difference is that if irq_safe is set then the callback routine is
invoked with interrupts disabled (and in this case pm_runtime_resume
may be called in interrupt context -- normally it can be called only in
process context).

Alan Stern

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