linux-kernel - Re: [RFC PATCH] genirq: implement read_irq

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Message-ID: <alpine.LFD.2.00.1104160030480.2744@localhost6.localdomain6>
Date:	Sat, 16 Apr 2011 00:39:47 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Abhijeet Dharmapurikar <adharmap@...eaurora.org>
cc:	mathieu.desnoyers@...icios.com, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, dwalker@...o99.com,
	linux-arm-msm-owner@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [RFC PATCH] genirq: implement read_irq_line for interrupt
 lines

On Fri, 15 Apr 2011, Abhijeet Dharmapurikar wrote:

> Thomas Gleixner wrote:
> > On Fri, 15 Apr 2011, Abhijeet Dharmapurikar wrote:
> > 
> > > Some drivers need to know what the status of the interrupt line is.
> > > This is especially true for drivers that register a handler with
> > > IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING and in the handler they
> > > need to know which edge transition it was invoked for.
> > 
> > What's the purpose of this? How is that going to be used?
> 
> The main purpose is to know in the handler if it was invoked becuase of a
> rising edge or the falling edge.

Come on. That's not an explanation. I know that already and it does
not answer my question how this is going to be used. IOW: What does
the driver do aside of knowing that it was a rising falling edge?
 
> Now one could say that the driver should maintain some state and toggle it
> upon each invocation of this handler. That scheme quickly goes out of sync
> because we might ignore interrupts while suspended.

Suspend is a totaly different issue. I have the impression that you
are trying to solve some basic issue at the driver level again - just
this time you add some core helper to get it solved.

Can you please show _AND_ explain the code which is going to use this?

Thanks,

	tglx
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