linux-kernel - Re: [RFC IRQ] genirq: fix handle_nested

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Date:	Thu, 28 Oct 2010 20:52:54 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Abhijeet Dharmapurikar <adharmap@...eaurora.org>
cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, linux-arm-msm-owner@...r.kernel.org
Subject: Re: [RFC IRQ] genirq: fix handle_nested_irq for lazy disable

On Thu, 28 Oct 2010, Abhijeet Dharmapurikar wrote:
> Thomas Gleixner wrote:
> > Aside of that this wont work for edge triggered interrupts, as you'd
> > loose the edge, so this needs more thought and a thorough look at the
> > users of handle_nested_irq().
> 
> I didn't understand this though. This patch will mask the interrupt in the
> controller even if it were edge. My interrupt controller latches
> edges and wants a mask (or an ack) to be executed to deactivate the line
> summary line. Do you mean that I should mark the interrupt IRQ_PENDING if it
> were an edge before masking it? If not, can you please explain.

See handle_edge_irq().

An edge is a one time event. Once you mask/ack it, it's gone. So now
when you unmask it won't reissue the interrupt on the hardware
level. Level interrupts do, as the mask does not affect that.

Thanks,

	tglx
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