linux-kernel - Re: [PATCH 20/62] sparc: irq: Remove IRQF

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Date:	Wed, 7 Sep 2011 19:33:52 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	David Miller <davem@...emloft.net>
cc:	yong.zhang0@...il.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	joe@...ches.com, sparclinux@...r.kernel.org
Subject: Re: [PATCH 20/62] sparc: irq: Remove IRQF_DISABLED



On Wed, 7 Sep 2011, Thomas Gleixner wrote:

> On Wed, 7 Sep 2011, David Miller wrote:
> 
> > From: Yong Zhang <yong.zhang0@...il.com>
> > Date: Wed,  7 Sep 2011 16:10:17 +0800
> > 
> > > This flag is a NOOP and can be removed now.
> > > 
> > > Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
> > 
> > How are things working now, if that is the case?
> > 
> > Specifically in the ldc_bind() case, we're passing iRQF_DISABLED here
> > so that the IRQ is not turned on when we request the IRQ, we later do
> > enable_irq() on these after we've take the spinlock in this function.
> > 
> > The IRQ cannot be allowed to be delivered between the request_irq()
> > call and the enable_irq() calls.
> > 
> > This sequence is necessary to deal with some lock ordering issues.
> 
> IRQF_DISABLED was telling the core code that the interrupt must run
> with interrupts disabled. As we enforced running all handlers with
> interrupts disabled the flag is meaningless. It was defined as 0
> anyway.
> 
> What you need to prevent that request_irq() enables the interrupt
> unconditionally, is to set IRQ_NOAUTOEN on the interrupt, which can't
> be handed in to request_irq(). You want to call
> 
>    irq_set_status_flags(irq, IRQ_NOAUTOEN);
> 
> for that irq. That tells request_irq() to leave the interrupt disabled
> and you have to explicitely enable it. That has not changed since we
> generalized the irq core code back in 2006.

If that's an issue, then we can create an IRQF_NOAUTOEN flag, which
can be handed into request_irq().

Thanks,

	tglx
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