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  * ----------------------------------------------------------------------------
    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 
   10 #include <sys/cdefs.h>
   11 __FBSDID("$FreeBSD: stable/9/sys/i386/i386/mp_clock.c 170289 2007-06-04 18:25:08Z dwmalone $");
   12 
   13 /*-
   14  * Just when we thought life were beautiful, reality pops its grim face over
   15  * the edge again:
   16  *
   17  * ] 20. ACPI Timer Errata
   18  * ]
   19  * ]   Problem: The power management timer may return improper result when
   20  * ]   read. Although the timer value settles properly after incrementing,
   21  * ]   while incrementing there is a 3nS window every 69.8nS where the
   22  * ]   timer value is indeterminate (a 4.2% chance that the data will be
   23  * ]   incorrect when read). As a result, the ACPI free running count up
   24  * ]   timer specification is violated due to erroneous reads.  Implication:
   25  * ]   System hangs due to the "inaccuracy" of the timer when used by
   26  * ]   software for time critical events and delays.
   27  * ] 
   28  * ] Workaround: Read the register twice and compare.
   29  * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
   30  *
   31  * The counter is in other words not latched to the PCI bus clock when
   32  * read.  Notice the workaround isn't:  We need to read until we have
   33  * three monotonic samples and then use the middle one, otherwise we are
   34  * not protected against the fact that the bits can be wrong in two
   35  * directions.  If we only cared about monosity two reads would be enough.
   36  */
   37 
   38 /* #include "opt_bus.h" */
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/timetc.h>
   43 #include <sys/kernel.h>
   44 #include <sys/module.h>
   45 #include <sys/sysctl.h>
   46 #include <sys/bus.h>
   47 
   48 #include <dev/pci/pcireg.h>
   49 #include <dev/pci/pcivar.h>
   50 
   51 static unsigned piix_get_timecount(struct timecounter *tc);
   52 
   53 static u_int32_t piix_timecounter_address;
   54 static u_int piix_freq = 14318182/4;
   55 
   56 static struct timecounter piix_timecounter = {
   57         piix_get_timecount,     /* get_timecount */
   58         0,                      /* no poll_pps */
   59         0xffffff,               /* counter_mask */
   60         0,                      /* frequency */
   61         "PIIX"                  /* name */
   62 };
   63 
   64 
   65 static int
   66 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
   67 {
   68         int error;
   69         u_int freq;
   70 
   71         if (piix_timecounter.tc_frequency == 0)
   72                 return (EOPNOTSUPP);
   73         freq = piix_freq;
   74         error = sysctl_handle_int(oidp, &freq, 0, req);
   75         if (error == 0 && req->newptr != NULL) {
   76                 piix_freq = freq;
   77                 piix_timecounter.tc_frequency = piix_freq;
   78         }
   79         return (error);
   80 }
   81 
   82 SYSCTL_PROC(_machdep, OID_AUTO, piix_freq, CTLTYPE_INT | CTLFLAG_RW,
   83     0, sizeof(u_int), sysctl_machdep_piix_freq, "I", "");
   84 
   85 static unsigned
   86 piix_get_timecount(struct timecounter *tc)
   87 {
   88         unsigned u1, u2, u3;
   89 
   90         u2 = inl(piix_timecounter_address);
   91         u3 = inl(piix_timecounter_address);
   92         do {
   93                 u1 = u2;
   94                 u2 = u3;
   95                 u3 = inl(piix_timecounter_address);
   96         } while (u1 > u2 || u2 > u3);
   97         return (u2);
   98 }
   99 
  100 static int
  101 piix_probe(device_t dev)
  102 {
  103         u_int32_t d;
  104 
  105         if (devclass_get_device(devclass_find("acpi"), 0) != NULL)
  106                 return (ENXIO);
  107         switch (pci_get_devid(dev)) {
  108         case 0x71138086:
  109                 device_set_desc(dev, "PIIX Timecounter");
  110                 break;
  111         default:
  112                 return (ENXIO);
  113         }
  114 
  115         d = pci_read_config(dev, PCIR_COMMAND, 2);
  116         if (!(d & PCIM_CMD_PORTEN)) {
  117                 device_printf(dev, "PIIX I/O space not mapped\n");
  118                 return (ENXIO);
  119         }
  120         return (0);
  121 }
  122 
  123 static int
  124 piix_attach(device_t dev)
  125 {
  126         u_int32_t d;
  127 
  128         d = pci_read_config(dev, 0x40, 4);
  129         piix_timecounter_address = (d & 0xffc0) + 8;
  130         piix_timecounter.tc_frequency = piix_freq;
  131         tc_init(&piix_timecounter);
  132         return (0);
  133 }
  134 
  135 static device_method_t piix_methods[] = {
  136         /* Device interface */
  137         DEVMETHOD(device_probe,         piix_probe),
  138         DEVMETHOD(device_attach,        piix_attach),
  139         { 0, 0 }
  140 };
  141 
  142 static driver_t piix_driver = {
  143         "piix",
  144         piix_methods,
  145         1,
  146 };
  147 
  148 static devclass_t piix_devclass;
  149 
  150 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);

Cache object: 605ffa24efe8182c40e1c777cb6756ea


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