sys/platform/pc32/i386/mp_clock.c

   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: 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 05:42:16 dillon Exp $
  34  *
  35  */
  36
  37 /* #include "opt_bus.h" */
  38
  39 #include <sys/param.h>
  40 #include <sys/systm.h>
  41 #include <sys/time.h>
  42 #include <sys/kernel.h>
  43 #include <sys/sysctl.h>
  44 #include <sys/bus.h>
  45
  46 #include <bus/pci/pcivar.h>
  47
  48 #if 0
  49
  50 static unsigned piix_get_timecount(struct timecounter *tc);
  51
  52 static u_int32_t piix_timecounter_address;
  53 static u_int piix_freq = 14318182/4;
  54
  55 static struct timecounter piix_timecounter = {
  56         piix_get_timecount,
  57         0,
  58         0xffffff,
  59         0,
  60         "PIIX"
  61 };
  62
  63 SYSCTL_OPAQUE(_debug, OID_AUTO, piix_timecounter, CTLFLAG_RD,
  64         &piix_timecounter, sizeof(piix_timecounter), "S,timecounter", "");
  65
  66 static int
  67 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
  68 {
  69         int error;
  70         u_int freq;
  71
  72         if (piix_timecounter.tc_frequency == 0)
  73                 return (EOPNOTSUPP);
  74         freq = piix_freq;
  75         error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
  76         if (error == 0 && req->newptr != NULL) {
  77                 piix_freq = freq;
  78                 piix_timecounter.tc_frequency = piix_freq;
  79                 update_timecounter(&piix_timecounter);
  80         }
  81         return (error);
  82 }
  83
  84 SYSCTL_PROC(_machdep, OID_AUTO, piix_freq, CTLTYPE_INT | CTLFLAG_RW,
  85     0, sizeof(u_int), sysctl_machdep_piix_freq, "I", "");
  86
  87 static unsigned
  88 piix_get_timecount(struct timecounter *tc)
  89 {
  90         unsigned u1, u2, u3;
  91
  92         u2 = inl(piix_timecounter_address);
  93         u3 = inl(piix_timecounter_address);
  94         do {
  95                 u1 = u2;
  96                 u2 = u3;
  97                 u3 = inl(piix_timecounter_address);
  98         } while (u1 > u2 || u2 > u3);
  99         return (u2);
 100 }
 101
 102 static int
 103 piix_probe (device_t dev)
 104 {
 105         u_int32_t       d;
 106
 107         switch (pci_get_devid(dev)) {
 108         case 0x71138086:
 109                 d = pci_read_config(dev, 0x4, 2);
 110                 if (!(d & 1))
 111                         return 0;       /* IO space not mapped */
 112                 d = pci_read_config(dev, 0x40, 4);
 113                 piix_timecounter_address = (d & 0xffc0) + 8;
 114                 piix_timecounter.tc_frequency = piix_freq;
 115                 init_timecounter(&piix_timecounter);
 116                 return (ENXIO);
 117         };
 118         return (ENXIO);
 119 }
 120
 121 static int
 122 piix_attach (device_t dev)
 123 {
 124
 125         return 0;
 126 }
 127
 128 static device_method_t piix_methods[] = {
 129         /* Device interface */
 130         DEVMETHOD(device_probe,         piix_probe),
 131         DEVMETHOD(device_attach,        piix_attach),
 132         { 0, 0 }
 133 };
 134
 135 static driver_t piix_driver = {
 136         "piix",
 137         piix_methods,
 138         1,
 139 };
 140
 141 static devclass_t piix_devclass;
 142
 143 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);
 144
 145 #endif
 146