2 * SPDX-License-Identifier: Beerware
4 * ----------------------------------------------------------------------------
5 * "THE BEER-WARE LICENSE" (Revision 42):
6 * <phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
7 * can do whatever you want with this stuff. If we meet some day, and you think
8 * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
9 * ----------------------------------------------------------------------------
12 #include <sys/cdefs.h>
13 __FBSDID("$FreeBSD$");
16 * Just when we thought life were beautiful, reality pops its grim face over
19 * ] 20. ACPI Timer Errata
21 * ] Problem: The power management timer may return improper result when
22 * ] read. Although the timer value settles properly after incrementing,
23 * ] while incrementing there is a 3nS window every 69.8nS where the
24 * ] timer value is indeterminate (a 4.2% chance that the data will be
25 * ] incorrect when read). As a result, the ACPI free running count up
26 * ] timer specification is violated due to erroneous reads. Implication:
27 * ] System hangs due to the "inaccuracy" of the timer when used by
28 * ] software for time critical events and delays.
30 * ] Workaround: Read the register twice and compare.
31 * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
33 * The counter is in other words not latched to the PCI bus clock when
34 * read. Notice the workaround isn't: We need to read until we have
35 * three monotonic samples and then use the middle one, otherwise we are
36 * not protected against the fact that the bits can be wrong in two
37 * directions. If we only cared about monosity two reads would be enough.
40 /* #include "opt_bus.h" */
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/timetc.h>
45 #include <sys/kernel.h>
46 #include <sys/module.h>
47 #include <sys/sysctl.h>
50 #include <dev/pci/pcireg.h>
51 #include <dev/pci/pcivar.h>
53 static unsigned piix_get_timecount(struct timecounter *tc);
55 static u_int32_t piix_timecounter_address;
56 static u_int piix_freq = 14318182/4;
58 static struct timecounter piix_timecounter = {
59 piix_get_timecount, /* get_timecount */
61 0xffffff, /* counter_mask */
67 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
72 if (piix_timecounter.tc_frequency == 0)
75 error = sysctl_handle_int(oidp, &freq, 0, req);
76 if (error == 0 && req->newptr != NULL) {
78 piix_timecounter.tc_frequency = piix_freq;
83 SYSCTL_PROC(_machdep, OID_AUTO, piix_freq,
84 CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 0, sizeof(u_int),
85 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 if (devclass_get_device(devclass_find("acpi"), 0) != NULL)
110 switch (pci_get_devid(dev)) {
112 device_set_desc(dev, "PIIX Timecounter");
118 d = pci_read_config(dev, PCIR_COMMAND, 2);
119 if (!(d & PCIM_CMD_PORTEN)) {
120 device_printf(dev, "PIIX I/O space not mapped\n");
127 piix_attach(device_t dev)
131 d = pci_read_config(dev, 0x40, 4);
132 piix_timecounter_address = (d & 0xffc0) + 8;
133 piix_timecounter.tc_frequency = piix_freq;
134 tc_init(&piix_timecounter);
138 static device_method_t piix_methods[] = {
139 /* Device interface */
140 DEVMETHOD(device_probe, piix_probe),
141 DEVMETHOD(device_attach, piix_attach),
145 static driver_t piix_driver = {
151 static devclass_t piix_devclass;
153 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);