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

From: Mark Rutland <mark.rutland@arm.com>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jason Cooper <jason@lakedaemon.net>,
	Nicolas Ferre <nicolas.ferre@atmel.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
	Alexandre Belloni <alexandre.belloni@free-electrons.com>,
	Rob Herring <robh+dt@kernel.org>, Pawel Moll <Pawel.Moll@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kumar Gala <galak@codeaurora.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip
Date: Wed, 11 Feb 2015 16:32:31 +0000	[thread overview]
Message-ID: <20150211163231.GR9154@leverpostej> (raw)
In-Reply-To: <20150211171515.55d5066f@bbrezillon>

On Wed, Feb 11, 2015 at 04:15:15PM +0000, Boris Brezillon wrote:
> On Wed, 11 Feb 2015 15:57:20 +0000
> Mark Rutland <mark.rutland@arm.com> wrote:
> 
> > [...]
> > 
> > > > > > 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.
> 
> Okay then, is anyone taking care of submitting such a patch (Mark ?) ?

I'll have the core patch shortly.

I'll need to ask for your help tagging the relevant drivers and testing.

Thanks,
Mark.