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-rw-r--r--Documentation/DocBook/uio-howto.tmpl40
-rw-r--r--drivers/uio/uio.c26
-rw-r--r--include/linux/uio_driver.h2
3 files changed, 67 insertions, 1 deletions
diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index fdd7f4f887b7..c4d187313963 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -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 @@ 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 +392,14 @@ 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>
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 5a7ca2e6094d..3a6934bf7131 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -427,6 +427,31 @@ static ssize_t uio_read(struct file *filep, char __user *buf,
return retval;
}
+static ssize_t uio_write(struct file *filep, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct uio_listener *listener = filep->private_data;
+ struct uio_device *idev = listener->dev;
+ ssize_t retval;
+ s32 irq_on;
+
+ if (idev->info->irq == UIO_IRQ_NONE)
+ return -EIO;
+
+ if (count != sizeof(s32))
+ return -EINVAL;
+
+ if (!idev->info->irqcontrol)
+ return -ENOSYS;
+
+ if (copy_from_user(&irq_on, buf, count))
+ return -EFAULT;
+
+ retval = idev->info->irqcontrol(idev->info, irq_on);
+
+ return retval ? retval : sizeof(s32);
+}
+
static int uio_find_mem_index(struct vm_area_struct *vma)
{
int mi;
@@ -546,6 +571,7 @@ static const struct file_operations uio_fops = {
.open = uio_open,
.release = uio_release,
.read = uio_read,
+ .write = uio_write,
.mmap = uio_mmap,
.poll = uio_poll,
.fasync = uio_fasync,
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 973386d439da..cf65e964102b 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -53,6 +53,7 @@ struct uio_device;
* @mmap: mmap operation for this uio device
* @open: open operation for this uio device
* @release: release operation for this uio device
+ * @irqcontrol: disable/enable irqs when 0/1 is written to /dev/uioX
*/
struct uio_info {
struct uio_device *uio_dev;
@@ -66,6 +67,7 @@ struct uio_info {
int (*mmap)(struct uio_info *info, struct vm_area_struct *vma);
int (*open)(struct uio_info *info, struct inode *inode);
int (*release)(struct uio_info *info, struct inode *inode);
+ int (*irqcontrol)(struct uio_info *info, s32 irq_on);
};
extern int __must_check