linux-kernel - Re: [RFC][PATCH] irq: support IRQ_NESTED_THREAD with non-threaded interrupt handlers

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Date:	Sat, 5 Jun 2010 18:18:16 +0100
From:	Marc Zyngier <maz@...terjones.org>
To:	Esben Haabendal <esbenhaabendal@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Esben Haabendal <eha@...edevelopment.dk>,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	joachim.eastwood@...ron.com
Subject: Re: [RFC][PATCH] irq: support IRQ_NESTED_THREAD with non-threaded 
 interrupt handlers

On Sat, 5 Jun 2010 18:53:53 +0200
Esben Haabendal <esbenhaabendal@...il.com> wrote:

> On Sat, Jun 5, 2010 at 4:10 PM, Marc Zyngier <maz@...terjones.org> wrote:
> > On Sat, 5 Jun 2010 15:56:01 +0200
> > Esben Haabendal <esbenhaabendal@...il.com> wrote:
> >
> >> I have a board with an I2C PCA9535 chip with two PHY interrupt lines
> >> hooked up to. The pca953x driver calls set_irq_nested_thread on all
> >> irq's on initialization. The PHY driver then calls request_irq, and has
> >> no idea that it should actually be using a threaded handler.
> >>
> >> With this patch, the PHY driver is able to work in this scenario
> >> without changes (and so should any other driver using request_irq).
> >
> > You may want to give request_any_context_irq() a try (available since
> > the latest merge window). It still requires your driver to be changed,
> > but it should then work in both threaded and non-threaded cases.
> 
> The problem is not in "my" driver, but in the phy driver framework in this
> particular case.

To me, any driver/subsystem/whatever qualifies as "yours" if you're taking
care of it ;-).

> What is the plan here, should all drivers change from
> request_any_context_irq() at some point in time?

All? Probably not. Only the few where the need arises, and after carefully
checking that you're not introducing a horrible race condition somewhere
(threaded handlers are running with interrupts enabled...).

	M.
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