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: head/sys/i386/i386/mp_clock.c 326408 2017-11-30 20:33:45Z pfg $");
   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 
   67 static int
   68 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
   69 {
   70         int error;
   71         u_int freq;
   72 
   73         if (piix_timecounter.tc_frequency == 0)
   74                 return (EOPNOTSUPP);
   75         freq = piix_freq;
   76         error = sysctl_handle_int(oidp, &freq, 0, req);
   77         if (error == 0 && req->newptr != NULL) {
   78                 piix_freq = freq;
   79                 piix_timecounter.tc_frequency = piix_freq;
   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         if (devclass_get_device(devclass_find("acpi"), 0) != NULL)
  108                 return (ENXIO);
  109         switch (pci_get_devid(dev)) {
  110         case 0x71138086:
  111                 device_set_desc(dev, "PIIX Timecounter");
  112                 break;
  113         default:
  114                 return (ENXIO);
  115         }
  116 
  117         d = pci_read_config(dev, PCIR_COMMAND, 2);
  118         if (!(d & PCIM_CMD_PORTEN)) {
  119                 device_printf(dev, "PIIX I/O space not mapped\n");
  120                 return (ENXIO);
  121         }
  122         return (0);
  123 }
  124 
  125 static int
  126 piix_attach(device_t dev)
  127 {
  128         u_int32_t d;
  129 
  130         d = pci_read_config(dev, 0x40, 4);
  131         piix_timecounter_address = (d & 0xffc0) + 8;
  132         piix_timecounter.tc_frequency = piix_freq;
  133         tc_init(&piix_timecounter);
  134         return (0);
  135 }
  136 
  137 static device_method_t piix_methods[] = {
  138         /* Device interface */
  139         DEVMETHOD(device_probe,         piix_probe),
  140         DEVMETHOD(device_attach,        piix_attach),
  141         { 0, 0 }
  142 };
  143 
  144 static driver_t piix_driver = {
  145         "piix",
  146         piix_methods,
  147         1,
  148 };
  149 
  150 static devclass_t piix_devclass;
  151 
  152 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);

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