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

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Date:	Fri, 23 May 2008 11:36:50 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Hans J. Koch" <hjk@...utronix.de>
Cc:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>,
	<linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jan Altenberg <jan.altenberg@...utronix.de>,
	Thomas Gleixner <tglx@...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 13:55:57 +0200 Hans J. Koch wrote:

>  Documentation/DocBook/uio-howto.tmpl |   40 ++++++++++++++++++++++++++++++++++-
>  drivers/uio/uio.c                    |   26 ++++++++++++++++++++++
>  include/linux/uio_driver.h           |    2 +
>  3 files changed, 67 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.26-rc/Documentation/DocBook/uio-howto.tmpl
> ===================================================================
> --- linux-2.6.26-rc.orig/Documentation/DocBook/uio-howto.tmpl	2008-05-22 20:22:57.000000000 +0200
> +++ linux-2.6.26-rc/Documentation/DocBook/uio-howto.tmpl	2008-05-23 11:57:23.000000000 +0200
> @@ -30,6 +30,12 @@
>  
>  <revhistory>
>  	<revision>
> +	<revnumber>0.5</revnumber>
> +	<date>2008-05-22</date>
> +	<authorinitials>hjk</authorinitials>
> +	<revremark>Added description of write() function.</revremark>
> +	</revision>
> +	<revision>
>  	<revnumber>0.4</revnumber>
>  	<date>2007-11-26</date>
>  	<authorinitials>hjk</authorinitials>
> @@ -64,7 +70,7 @@
>  <?dbhtml filename="copyright.html"?>
>  <title>Copyright and License</title>
>  <para>
> -      Copyright (c) 2006 by Hans-Jürgen Koch.</para>
> +      Copyright (c) 2006-2008 by Hans-Jürgen Koch.</para>
>  <para>
>  This documentation is Free Software licensed under the terms of the
>  GPL version 2.
> @@ -189,6 +195,30 @@
>  	represents the total interrupt count. You can use this number
>  	to figure out if you missed some interrupts.
>  	</para>
> +	<para>
> +	For some hardware that has more than one interrupt source internally,
> +	but not seperate IRQ mask and status registers, there might be

	        separate

> +	situations where userspace cannot determine what the interrupt source
> +	was if the kernel handler disables them by writing to the chip's IRQ
> +	register. In such a case, the kernel has to disable the IRQ completely
> +	to leave the chip's register untouched. Now the userspace part can
> +	determine the cause of the interrupt, but it cannot re-enable
> +	interrupts. Another cornercase are chips where re-enabling interrupts

	                               is

> +	is a read-modify-write operation to a combined IRQ status/acknowledge
> +	register. This would be racy if a new interrupt occured

	                                                occurred

> +	simultaneously.
> +	</para>
> +	<para>
> +	To address these problems, UIO also implements a write() function. It
> +	is normally not used and can be ignored for hardware that has only a
> +	single interrupt source or has seperate IRQ mask and status registers.

	                               separate
["There's <a rat> in separate."]

> +	If you need it, however, a write to <filename>/dev/uioX</filename>
> +	will call the <function>irqcontrol()</function> function implemented
> +	by the driver. You have to write a 32-bit value that is usually either
> +	0 or 1 do disable or enable interrupts. If a driver does not implement

	       to

> +	<function>irqcontrol()</function>, <function>write()</function> will
> +	return with <varname>-ENOSYS</varname>.
> +	</para>

---
~Randy
--
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