aboutsummaryrefslogtreecommitdiff
path: root/Documentation/DocBook/uio-howto.tmpl
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/DocBook/uio-howto.tmpl')
-rw-r--r--Documentation/DocBook/uio-howto.tmpl63
1 files changed, 51 insertions, 12 deletions
diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index fdd7f4f887b..df87d1b9360 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -21,6 +21,18 @@
</affiliation>
</author>
+<copyright>
+ <year>2006-2008</year>
+ <holder>Hans-Jürgen Koch.</holder>
+</copyright>
+
+<legalnotice>
+<para>
+This documentation is Free Software licensed under the terms of the
+GPL version 2.
+</para>
+</legalnotice>
+
<pubdate>2006-12-11</pubdate>
<abstract>
@@ -30,6 +42,12 @@
<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>
@@ -57,20 +75,9 @@
</bookinfo>
<chapter id="aboutthisdoc">
-<?dbhtml filename="about.html"?>
+<?dbhtml filename="aboutthis.html"?>
<title>About this document</title>
-<sect1 id="copyright">
-<?dbhtml filename="copyright.html"?>
-<title>Copyright and License</title>
-<para>
- Copyright (c) 2006 by Hans-Jürgen Koch.</para>
-<para>
-This documentation is Free Software licensed under the terms of the
-GPL version 2.
-</para>
-</sect1>
-
<sect1 id="translations">
<?dbhtml filename="translations.html"?>
<title>Translations</title>
@@ -189,6 +196,30 @@ interested in translating it, please email me
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 separate IRQ mask and status registers, there might be
+ 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 is chips where re-enabling interrupts
+ is a read-modify-write operation to a combined IRQ status/acknowledge
+ register. This would be racy if a new interrupt 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 separate IRQ mask and status registers.
+ 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 to disable or enable interrupts. If a driver does not implement
+ <function>irqcontrol()</function>, <function>write()</function> will
+ return with <varname>-ENOSYS</varname>.
+ </para>
<para>
To handle interrupts properly, your custom kernel module can
@@ -362,6 +393,14 @@ device is actually used.
<function>open()</function>, you will probably also want a custom
<function>release()</function> function.
</para></listitem>
+
+<listitem><para>
+<varname>int (*irqcontrol)(struct uio_info *info, s32 irq_on)
+</varname>: Optional. If you need to be able to enable or disable
+interrupts from userspace by writing to <filename>/dev/uioX</filename>,
+you can implement this function. The parameter <varname>irq_on</varname>
+will be 0 to disable interrupts and 1 to enable them.
+</para></listitem>
</itemizedlist>
<para>