The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/mp_clock.c

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    1 /*-
    2  * SPDX-License-Identifier: Beerware
    3  *
    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  * ----------------------------------------------------------------------------
   10  */
   11 
   12 #include <sys/cdefs.h>
   13 __FBSDID("$FreeBSD$");
   14 
   15 /*-
   16  * Just when we thought life were beautiful, reality pops its grim face over
   17  * the edge again:
   18  *
   19  * ] 20. ACPI Timer Errata
   20  * ]
   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.
   29  * ] 
   30  * ] Workaround: Read the register twice and compare.
   31  * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
   32  *
   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.
   38  */
   39 
   40 /* #include "opt_bus.h" */
   41 
   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>
   48 #include <sys/bus.h>
   49 
   50 #include <dev/pci/pcireg.h>
   51 #include <dev/pci/pcivar.h>
   52 
   53 static unsigned piix_get_timecount(struct timecounter *tc);
   54 
   55 static u_int32_t piix_timecounter_address;
   56 static u_int piix_freq = 14318182/4;
   57 
   58 static struct timecounter piix_timecounter = {
   59         piix_get_timecount,     /* get_timecount */
   60         0,                      /* no poll_pps */
   61         0xffffff,               /* counter_mask */
   62         0,                      /* frequency */
   63         "PIIX"                  /* name */
   64 };
   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, 0, req);
   76         if (error == 0 && req->newptr != NULL) {
   77                 piix_freq = freq;
   78                 piix_timecounter.tc_frequency = piix_freq;
   79         }
   80         return (error);
   81 }
   82 
   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",
   86     "");
   87 
   88 static unsigned
   89 piix_get_timecount(struct timecounter *tc)
   90 {
   91         unsigned u1, u2, u3;
   92 
   93         u2 = inl(piix_timecounter_address);
   94         u3 = inl(piix_timecounter_address);
   95         do {
   96                 u1 = u2;
   97                 u2 = u3;
   98                 u3 = inl(piix_timecounter_address);
   99         } while (u1 > u2 || u2 > u3);
  100         return (u2);
  101 }
  102 
  103 static int
  104 piix_probe(device_t dev)
  105 {
  106         u_int32_t d;
  107 
  108         if (devclass_get_device(devclass_find("acpi"), 0) != NULL)
  109                 return (ENXIO);
  110         switch (pci_get_devid(dev)) {
  111         case 0x71138086:
  112                 device_set_desc(dev, "PIIX Timecounter");
  113                 break;
  114         default:
  115                 return (ENXIO);
  116         }
  117 
  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");
  121                 return (ENXIO);
  122         }
  123         return (0);
  124 }
  125 
  126 static int
  127 piix_attach(device_t dev)
  128 {
  129         u_int32_t d;
  130 
  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);
  135         return (0);
  136 }
  137 
  138 static device_method_t piix_methods[] = {
  139         /* Device interface */
  140         DEVMETHOD(device_probe,         piix_probe),
  141         DEVMETHOD(device_attach,        piix_attach),
  142         { 0, 0 }
  143 };
  144 
  145 static driver_t piix_driver = {
  146         "piix",
  147         piix_methods,
  148         1,
  149 };
  150 
  151 static devclass_t piix_devclass;
  152 
  153 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);

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