linux-kernel-driver-dev/interrupts2.html at master · txrxlabs/linux-kernel-driver-dev · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
<html>
<font face="helvetica">
<title>Interrupts (part 2)</title>
<body>
<p align=center><font size=+5>Interrupts (part 2)</font>
<hr>
<a href="contents.html">Contents</a>
<font size=+3>
<ul>
<li>How does the CPU know what function to call for a given IRQ?
The device driver tells it by request_irq(), declared in interrupts.h:
<pre>
	static inline int __must_check
	request_irq(unsigned int irq, irq_handler_t handler,
		unsigned long flags, const char *name, void *dev)
</pre>
<li>How does the device driver know which IRQ number to use?
We'll get to that in a minute.
<li>What does the irq_handler_t look like?  It looks like this:
<pre>
	static irqreturn_t my_handler(int irq, void *dev_id);
</pre>
<li>What does the handler function have to do?
Well, it depends on the device.  However, what it typically does is
something like this:
<pre>
	static irqreturn_t my_handler(int irq, void *dev_id)
	{
		struct mydata *mydevice = dev_id;
		unsigned long flags;

		if (this_interrupt_is_not_for_me(mydevice)) /* dev specific */
			return IRQ_NONE;

		spin_lock_irqsave(&amp;mydevice-&gt;lock, flags);
		process_the_interrupt(mydevice); /* device specific */
		spin_unlock_irqrestore(&amp;mydevice-&gt;lock, flags);
		return IRQ_HANDLED;
	}
</pre>
<li>How is that the dev_id parameter to my_handler is so conveniently
just exactly the information we need about our device?  Because the dev_id
parameter is exactly the same thing that we pass as the dev parameter
when we called request_irq().  In other words, we arrange for it to
be just the information we need.
</pre>
</ul>
</font>
</body>
</html>