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

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Date:	Sun, 25 May 2008 00:22:20 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Greg KH <gregkh@...e.de>
cc:	"Hans J. Koch" <hjk@...utronix.de>,
	Uwe Kleine-K??nig <Uwe.Kleine-Koenig@...i.com>,
	linux-kernel@...r.kernel.org,
	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 Fri, 23 May 2008, Greg KH wrote:

> On Fri, May 23, 2008 at 01:55:57PM +0200, Hans J. Koch wrote:
> > 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.
> 
> Why not just a new sysfs file for the uio device, irq_enabled, or
> something like that?  That way our main read/write path is left alone.

It makes a certain amount of sense to use write. You hold the device
file descriptor anyway for the read (wait for interrupt) operation,
so using the same file descriptor is not a too bad idea:

    while (!stop) {

        /* wait for interrupt */
	read(fd);

	do_stuff();

	/*reenable interrupt */
	write(fd);
    }

I thought about using a sysfs entry for a while, but looking at the
actual use case made the write() solution a more natural choice.

Thanks,

	tglx
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