linux-kernel - Re: [PATCH] gpio: add interrupt handling capability to max732x

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Date:	Sat, 20 Mar 2010 05:44:40 +0000
From:	Marc Zyngier <maz@...terjones.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Eric Miao <eric.y.miao@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jebediah Huang <jebediah.huang@...il.com>
Subject: Re: [PATCH] gpio: add interrupt handling capability to max732x

On Fri, 19 Mar 2010 16:41:56 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 16 Mar 2010 11:34:52 +0100
> Marc Zyngier <maz@...terjones.org> wrote:
> 
> > +static irqreturn_t max732x_irq_handler(int irq, void *devid)
> > +{
> > +	struct max732x_chip *chip = devid;
> > +	uint8_t pending;
> > +	uint8_t level;
> > +
> > +	pending = max732x_irq_pending(chip);
> > +
> > +	if (!pending)
> > +		return IRQ_HANDLED;
> 
> Should be IRQ_NONE?

The main problem is that some of the supported expanders do not have a
hardware interrupt mask, so the IRQ will fire on each input pin toggle,
including the ones we don't care about (pca953x has the same problem).

Returning IRQ_NONE will cause the irq core to quickly disable the line.
Not good either. I could add a test for the mask feature bit, and
return IRQ_NONE only in that case.

> If this device was on a shared interrupt line and the interrupt was
> caused by some other device, and this handler is called first then the
> incorrect IRQ_HANDLED return could cause the irq core to do wrong things.

This is exactly why the irq handler is requested without the SHARED
flag:

+		ret = request_threaded_irq(client->irq,
+					   NULL,
+					   max732x_irq_handler,
+					   IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
+					   dev_name(&client->dev), chip);

The same mask feature bit could be used to allow shared interrupts with
devices that support it.

Thanks,

	M.
-- 
I'm the slime oozin' out from your TV set...
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