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 * ----------------------------------------------------------------------------
9 * Just when we thought life were beautiful, reality pops its grim face over
12 * ] 20. ACPI Timer Errata
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.
23 * ] Workaround: Read the register twice and compare.
24 * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
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.
32 * $FreeBSD: src/sys/i386/i386/mp_clock.c,v 1.4.2.2 2000/09/30 02:49:32 ps Exp $
33 * $DragonFly: src/sys/platform/pc32/i386/mp_clock.c,v 1.4 2004/01/30 06:42:16 dillon Exp $
37 /* #include "opt_bus.h" */
38 /* #include "opt_pci.h" */
40 #include <sys/param.h>
41 #include <sys/systm.h>
43 #include <sys/kernel.h>
44 #include <sys/sysctl.h>
47 #include <bus/pci/pcivar.h>
51 static unsigned piix_get_timecount(struct timecounter
*tc
);
53 static u_int32_t piix_timecounter_address
;
54 static u_int piix_freq
= 14318182/4;
56 static struct timecounter piix_timecounter
= {
64 SYSCTL_OPAQUE(_debug
, OID_AUTO
, piix_timecounter
, CTLFLAG_RD
,
65 &piix_timecounter
, sizeof(piix_timecounter
), "S,timecounter", "");
68 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS
)
73 if (piix_timecounter
.tc_frequency
== 0)
76 error
= sysctl_handle_int(oidp
, &freq
, sizeof(freq
), req
);
77 if (error
== 0 && req
->newptr
!= NULL
) {
79 piix_timecounter
.tc_frequency
= piix_freq
;
80 update_timecounter(&piix_timecounter
);
85 SYSCTL_PROC(_machdep
, OID_AUTO
, piix_freq
, CTLTYPE_INT
| CTLFLAG_RW
,
86 0, sizeof(u_int
), sysctl_machdep_piix_freq
, "I", "");
89 piix_get_timecount(struct timecounter
*tc
)
93 u2
= inl(piix_timecounter_address
);
94 u3
= inl(piix_timecounter_address
);
98 u3
= inl(piix_timecounter_address
);
99 } while (u1
> u2
|| u2
> u3
);
104 piix_probe (device_t dev
)
108 switch (pci_get_devid(dev
)) {
110 d
= pci_read_config(dev
, 0x4, 2);
112 return 0; /* IO space not mapped */
113 d
= pci_read_config(dev
, 0x40, 4);
114 piix_timecounter_address
= (d
& 0xffc0) + 8;
115 piix_timecounter
.tc_frequency
= piix_freq
;
116 init_timecounter(&piix_timecounter
);
123 piix_attach (device_t dev
)
129 static device_method_t piix_methods
[] = {
130 /* Device interface */
131 DEVMETHOD(device_probe
, piix_probe
),
132 DEVMETHOD(device_attach
, piix_attach
),
136 static driver_t piix_driver
= {
142 static devclass_t piix_devclass
;
144 DRIVER_MODULE(piix
, pci
, piix_driver
, piix_devclass
, 0, 0);