Commit 328a14e7 authored by Hans J. Koch's avatar Hans J. Koch Committed by Greg Kroah-Hartman
Browse files

UIO: Add write function to allow irq masking 



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.

Signed-off-by: default avatarHans J. Koch <hjk@linutronix.de>
Acked-by: default avatarUwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Acked-by: default avatarMagnus Damm <damm@igel.co.jp>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 934da476

Documentation/DocBook/uio-howto.tmpl

+39 −1
Original line number Diff line number Diff line
@@ -29,6 +29,12 @@ 
</abstract>



<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>
@@ -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>

drivers/uio/uio.c

+26 −0
Original line number Diff line number Diff line
@@ -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,

include/linux/uio_driver.h

+2 −0
Original line number Diff line number Diff line
@@ -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

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