linux-kernel - Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip

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Message-ID: <20150211155720.GQ9154@leverpostej>
Date:	Wed, 11 Feb 2015 15:57:20 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <Pawel.Moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq
 demuxer chip

[...]

> > > > So for the flag at request time approach to work, all the drivers using
> > > > the interrupt would have to flag they're safe in that context.
> > > 
> > > Something like IRQF_"I can share the line with a timer" I guess?  That wouldn't
> > > hurt and can be checked at request time even.
> > 
> > I guess that would have to imply IRQF_SHARED, so we'd have something
> > like:
> > 
> > IRQF_SHARED_SUSPEND_OK - This handler is safe to call spuriously during
> > 			 suspend in the case the line is shared. The
> > 			 handler will not access unavailable hardware
> > 			 or kernel infrastructure during this period.
> > 
> > #define __IRQF_SUSPEND_SPURIOUS		0x00040000
> > #define	IRQF_SHARED_SUSPEND_OK		(IRQF_SHARED | __IRQF_SUSPEND_SPURIOUS)
> 
> What about
> 
> #define __IRQF_TIMER_SIBLING_OK	0x00040000
> #define	IRQF_SHARED_TIMER_OK	(IRQF_SHARED | __IRQF_TIMER_SIBLING_OK)
> 
> The "suspend" part is kind of a distraction to me here, because that really
> only is about sharing an IRQ with a timer and the "your interrupt handler
> may be called when the device is suspended" part is just a consequence of that.

My rationale was that you didn't really care who else was using the IRQ
(e.g. the timer); you're just stating that you can survive being called
during suspend (which is what the driver may need to check for in the
handler if the device happens to be powered down or whatever).

So I guess I see it the other way around. This is essentially claiming
we can handle sharing with IRQF_NO_SUSPEND rather than IRQF_TIMER.

> So IMO it's better to have "TIMER" in the names to avoid encouraging people to
> abuse this for other purposes not related to timers.

In the end a name is a name, and if you think IRQF_SHARED_TIMER_OK is
better I shan't complain.

The fundamental issue I'm concerned with is addressed by this approach.

Thanks,
Mark.
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