linux-kernel - Re: [PATCH/RFC 00/03] irqchip: renesas-irqc: Fine grained Runtime PM support

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Date:	Thu, 23 Apr 2015 10:44:44 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
cc:	Magnus Damm <magnus.damm@...il.com>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Simon Horman <horms@...ge.net.au>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH/RFC 00/03] irqchip: renesas-irqc: Fine grained Runtime
 PM support

On Thu, 23 Apr 2015, Geert Uytterhoeven wrote:

> >> I'm afraid you can't call pm_runtime_get_sync() from these methods, as
> >> they may be called from interrupt context.
> >
> > Ouch. I know the clock framework has prepare/enable separated with
> > context, but with the irqchip callbacks I suppose no such separation
> 
> It's not the clock operations, but the pm_runtime operations that cannot be
> called from interrupt context.

In fact the pm_runtime operations _can_ be called from interrupt
context, provided the driver has first invoked pm_runtime_irq_safe().  
Of course, this requires that none of the runtime-PM callback routines
ever sleep or perform a blocking operation.

This is all explained in Documentation/power/runtime_pm.txt (search for 
"irq_safe").

Alan Stern

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