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

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Date:	Sun, 8 Mar 2015 11:41:31 -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 Fri, 6 Mar 2015, Tony Lindgren wrote:

> > > I'll verify again, but I believe the issue was that without doing
> > > mark_last_busy here the device falls back asleep right away.

As it should.  If you don't increment the usage counter (for example, 
by calling pm_runtime_get instead of pm_request_resume) and you don't 
update last_busy then you are telling the PM core that the device 
currently isn't busy and it hasn't been in use since the last time it 
was suspended.  Under those circumstances, the PM core is _supposed_ to 
suspend the device right away.

> > > That probably should be fixed in pm_runtime in general if that's
> > > the case.
> > 
> > It's up to the subsystem to handle this.  For example, the USB 
> > subsystem's runtime-resume routine calls pm_runtime_mark_last_busy.
> 
> Hmm.. OK thanks this probably explains why pm_request_resume() did
> not work.
> 
> For omaps, I could call this from the interconnect related code,
> but then how dow we deal with the subsystems that don't call it?

Start by determining _why_ they don't call it.  Maybe they have a good 
reason.  If they don't then fix them.

> > > 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 I'll take a look if we can just call
> pm_request_resume() and disable_irq() on the wakeirq in without
> waiting for the device driver runtime_suspend to disable the wakeirq.
> That would minimize the interface to just dev_pm_request_wakeirq()
> and dev_pm_free_wakeirq().

Will that be acceptable in systems with shared IRQ lines?

Alan Stern

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