linux-kernel - Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on slow busses

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Date:	Fri, 14 Aug 2009 11:03:18 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Trilok Soni <soni.trilok@...il.com>,
	Pavel Machek <pavel@....cz>,
	Brian Swetland <swetland@...gle.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	m.szyprowski@...sung.com, t.fujak@...sung.com,
	kyungmin.park@...sung.com, David Brownell <david-b@...bell.net>,
	Daniel Ribeiro <drwyrm@...il.com>, arve@...roid.com,
	Barry Song <21cnbao@...il.com>
Subject: Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on
 slow busses

On Fri, 14 Aug 2009, Peter Zijlstra wrote:
> On Thu, 2009-08-13 at 19:40 +0000, Thomas Gleixner wrote:
> >  
> > +/**
> > + *	disable_slowbus_irq - disable an slowbus irq and wait for completion
> > + *	@irq: Interrupt to disable
> > + *
> > + *	Disable the selected interrupt line.  Enables and Disables are
> > + *	nested.
> > + *	This function waits for any pending IRQ handlers for this interrupt
> > + *	to complete before returning. If you use this function while
> > + *	holding a resource the IRQ handler may need you will deadlock.
> > + *
> > + *	This function must not be called from IRQ context.
> > + */
> > +void disable_slowbus_irq(unsigned int irq)
> > +{
> > +	struct irq_desc *desc = irq_to_desc(irq);
> > +
> > +	if (!desc || !desc->chip || !desc->chip->bus_lock)
> > +		return;
> > +
> > +	desc->chip->bus_lock(irq);
> > +	disable_irq_nosync(irq);
> > +	if (desc->action)
> > +		synchronize_irq(irq);
> > +	desc->chip->bus_sync_unlock(irq);
> > +}
> > +EXPORT_SYMBOL(disable_slowbus_irq);
> 
> Should we also not check that desc->chip->bus_lock is not set for the
> regular function disable_irq()?
> 
> It seems to me mixing disable_irq() and disable_slowbus_irq() is a
> recipe for disaster.
> 
> Same for the other slowbus functions of course.

Yeah, that's what I wanted to avoid with the first version, which did
the conditional locking and did not require a separate API, but Ingo
frowned upon the conditional lock.

Thanks,

	tglx

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