mp_clock.c revision 62573 
1/*
2 * ----------------------------------------------------------------------------
3 * "THE BEER-WARE LICENSE" (Revision 42):
4 * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
5 * can do whatever you want with this stuff. If we meet some day, and you think
6 * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
7 * ----------------------------------------------------------------------------
8 *
9 * Just when we thought life were beautiful, reality pops its grim face over
10 * the edge again:
11 *
12 * ] 20. ACPI Timer Errata
13 * ]
14 * ]   Problem: The power management timer may return improper result when
15 * ]   read. Although the timer value settles properly after incrementing,
16 * ]   while incrementing there is a 3nS window every 69.8nS where the
17 * ]   timer value is indeterminate (a 4.2% chance that the data will be
18 * ]   incorrect when read). As a result, the ACPI free running count up
19 * ]   timer specification is violated due to erroneous reads.  Implication:
20 * ]   System hangs due to the "inaccuracy" of the timer when used by
21 * ]   software for time critical events and delays.
22 * ]
23 * ] Workaround: Read the register twice and compare.
24 * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
25 *
26 * The counter is in other words not latched to the PCI bus clock when
27 * read.  Notice the workaround isn't:  We need to read until we have
28 * three monotonic samples and then use the middle one, otherwise we are
29 * not protected against the fact that the bits can be wrong in two
30 * directions.  If we only cared about monosity two reads would be enough.
31 *
32 * $FreeBSD: head/sys/i386/i386/mp_clock.c 62573 2000-07-04 11:25:35Z phk $
33 *
34 */
35
36/* #include "opt_bus.h" */
37/* #include "opt_pci.h" */
38/* #include "opt_smp.h" */
39
40#include <sys/param.h>
41#include <sys/systm.h>
42#include <sys/timetc.h>
43#include <sys/kernel.h>
44#include <sys/sysctl.h>
45#include <sys/bus.h>
46
47#include <pci/pcivar.h>
48
49static unsigned piix_get_timecount(struct timecounter *tc);
50
51static u_int32_t piix_timecounter_address;
52static u_int piix_freq = 14318182/4;
53
54static struct timecounter piix_timecounter = {
55	piix_get_timecount,
56	0,
57	0xffffff,
58	0,
59	"PIIX"
60};
61
62SYSCTL_OPAQUE(_debug, OID_AUTO, piix_timecounter, CTLFLAG_RD,
63	&piix_timecounter, sizeof(piix_timecounter), "S,timecounter", "");
64
65static int
66sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
67{
68	int error;
69	u_int freq;
70
71	if (piix_timecounter.tc_frequency == 0)
72		return (EOPNOTSUPP);
73	freq = piix_freq;
74	error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
75	if (error == 0 && req->newptr != NULL) {
76		piix_freq = freq;
77		piix_timecounter.tc_frequency = piix_freq;
78		tc_update(&piix_timecounter);
79	}
80	return (error);
81}
82
83SYSCTL_PROC(_machdep, OID_AUTO, piix_freq, CTLTYPE_INT | CTLFLAG_RW,
84    0, sizeof(u_int), sysctl_machdep_piix_freq, "I", "");
85
86static unsigned
87piix_get_timecount(struct timecounter *tc)
88{
89	unsigned u1, u2, u3;
90
91	u2 = inl(piix_timecounter_address);
92	u3 = inl(piix_timecounter_address);
93	do {
94		u1 = u2;
95		u2 = u3;
96		u3 = inl(piix_timecounter_address);
97	} while (u1 > u2 || u2 > u3);
98	return (u2);
99}
100
101static int
102piix_probe (device_t dev)
103{
104	u_int32_t	d;
105
106	switch (pci_get_devid(dev)) {
107	case 0x71138086:
108		d = pci_read_config(dev, 0x4, 2);
109		if (!(d & 1))
110			return 0;	/* IO space not mapped */
111		d = pci_read_config(dev, 0x40, 4);
112		piix_timecounter_address = (d & 0xffc0) + 8;
113		piix_timecounter.tc_frequency = piix_freq;
114		tc_init(&piix_timecounter);
115		return (ENXIO);
116	};
117	return (ENXIO);
118}
119
120static int
121piix_attach (device_t dev)
122{
123
124	return 0;
125}
126
127static device_method_t piix_methods[] = {
128	/* Device interface */
129	DEVMETHOD(device_probe,		piix_probe),
130	DEVMETHOD(device_attach,	piix_attach),
131	{ 0, 0 }
132};
133
134static driver_t piix_driver = {
135	"piix",
136	piix_methods,
137	1,
138};
139
140static devclass_t piix_devclass;
141
142DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);
143