linux-kernel - Re: [PATCH 1/1] UIO: Add a write() function to enable/disable interrupts

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Message-ID: <alpine.LFD.1.10.0806040901400.3235@apollo.tec.linutronix.de>
Date:	Wed, 4 Jun 2008 09:05:43 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
cc:	Hans-Jürgen Koch <hjk@...utronix.de>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Jan Altenberg <jan.altenberg@...utronix.de>,
	Magnus Damm <magnus.damm@...il.com>
Subject: Re: [PATCH 1/1] UIO: Add a write() function to enable/disable
 interrupts

On Wed, 4 Jun 2008, Uwe Kleine-König wrote:
> Hello Hans-Jürgen,
> 
> > Sometimes it is necessary to enable/disable the interrupt of a UIO device
> > from the userspace part of the driver. With this patch, the UIO kernel driver
> > can implement an "irqcontrol()" function that does this. Userspace can write
> > an s32 value to /dev/uioX (usually 0 or 1 to turn the irq off or on). The
> > UIO core will then call the driver's irqcontrol function.
> IMHO it would make sense to demand that irqcontrol() is idempotent and
> then call irqcontrol(ON) before blocking in read and poll.

We thought about that, but it is racy. Also explicit control is way
better than automagic hackery.

Thanks,
	tglx