1What:		/sys/firmware/acpi/interrupts/
2Date:		February 2008
3Contact:	Len Brown <lenb@kernel.org>
4Description:
5		All ACPI interrupts are handled via a single IRQ,
6		the System Control Interrupt (SCI), which appears
7		as "acpi" in /proc/interrupts.
8
9		However, one of the main functions of ACPI is to make
10		the platform understand random hardware without
11		special driver support.  So while the SCI handles a few
12		well known (fixed feature) interrupts sources, such
13		as the power button, it can also handle a variable
14		number of a "General Purpose Events" (GPE).
15
16		A GPE vectors to a specified handler in AML, which
17		can do a anything the BIOS writer wants from
18		OS context.  GPE 0x12, for example, would vector
19		to a level or edge handler called _L12 or _E12.
20		The handler may do its business and return.
21		Or the handler may send send a Notify event
22		to a Linux device driver registered on an ACPI device,
23		such as a battery, or a processor.
24
25		To figure out where all the SCI's are coming from,
26		/sys/firmware/acpi/interrupts contains a file listing
27		every possible source, and the count of how many
28		times it has triggered.
29
30		$ cd /sys/firmware/acpi/interrupts
31		$ grep . *
32		error:	     0
33		ff_gbl_lock:	   0   enable
34		ff_pmtimer:	  0  invalid
35		ff_pwr_btn:	  0   enable
36		ff_rt_clk:	 2  disable
37		ff_slp_btn:	  0  invalid
38		gpe00:	     0	invalid
39		gpe01:	     0	 enable
40		gpe02:	   108	 enable
41		gpe03:	     0	invalid
42		gpe04:	     0	invalid
43		gpe05:	     0	invalid
44		gpe06:	     0	 enable
45		gpe07:	     0	 enable
46		gpe08:	     0	invalid
47		gpe09:	     0	invalid
48		gpe0A:	     0	invalid
49		gpe0B:	     0	invalid
50		gpe0C:	     0	invalid
51		gpe0D:	     0	invalid
52		gpe0E:	     0	invalid
53		gpe0F:	     0	invalid
54		gpe10:	     0	invalid
55		gpe11:	     0	invalid
56		gpe12:	     0	invalid
57		gpe13:	     0	invalid
58		gpe14:	     0	invalid
59		gpe15:	     0	invalid
60		gpe16:	     0	invalid
61		gpe17:	  1084	 enable
62		gpe18:	     0	 enable
63		gpe19:	     0	invalid
64		gpe1A:	     0	invalid
65		gpe1B:	     0	invalid
66		gpe1C:	     0	invalid
67		gpe1D:	     0	invalid
68		gpe1E:	     0	invalid
69		gpe1F:	     0	invalid
70		gpe_all:    1192
71		sci:	1194
72
73		sci - The total number of times the ACPI SCI
74		has claimed an interrupt.
75
76		gpe_all - count of SCI caused by GPEs.
77
78		gpeXX - count for individual GPE source
79
80		ff_gbl_lock - Global Lock
81
82		ff_pmtimer - PM Timer
83
84		ff_pwr_btn - Power Button
85
86		ff_rt_clk - Real Time Clock
87
88		ff_slp_btn - Sleep Button
89
90		error - an interrupt that can't be accounted for above.
91
92		invalid: it's either a wakeup GPE or a GPE/Fixed Event that
93			doesn't have an event handler.
94
95		disable: the GPE/Fixed Event is valid but disabled.
96
97		enable: the GPE/Fixed Event is valid and enabled.
98
99		Root has permission to clear any of these counters.  Eg.
100		# echo 0 > gpe11
101
102		All counters can be cleared by clearing the total "sci":
103		# echo 0 > sci
104
105		None of these counters has an effect on the function
106		of the system, they are simply statistics.
107
108		Besides this, user can also write specific strings to these files
109		to enable/disable/clear ACPI interrupts in user space, which can be
110		used to debug some ACPI interrupt storm issues.
111
112		Note that only writting to VALID GPE/Fixed Event is allowed,
113		i.e. user can only change the status of runtime GPE and
114		Fixed Event with event handler installed.
115
116		Let's take power button fixed event for example, please kill acpid
117		and other user space applications so that the machine won't shutdown
118		when pressing the power button.
119		# cat ff_pwr_btn
120		0
121		# press the power button for 3 times;
122		# cat ff_pwr_btn
123		3
124		# echo disable > ff_pwr_btn
125		# cat ff_pwr_btn
126		disable
127		# press the power button for 3 times;
128		# cat ff_pwr_btn
129		disable
130		# echo enable > ff_pwr_btn
131		# cat ff_pwr_btn
132		4
133		/*
134		 * this is because the status bit is set even if the enable bit is cleared,
135		 * and it triggers an ACPI fixed event when the enable bit is set again
136		 */
137		# press the power button for 3 times;
138		# cat ff_pwr_btn
139		7
140		# echo disable > ff_pwr_btn
141		# press the power button for 3 times;
142		# echo clear > ff_pwr_btn	/* clear the status bit */
143		# echo disable > ff_pwr_btn
144		# cat ff_pwr_btn
145		7
146
147