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  * 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  * $FreeBSD$
   33  *
   34  */
   35 
   36 /* #include "opt_bus.h" */
   37 /* #include "opt_pci.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 <pci/pcivar.h>
   47 
   48 static unsigned piix_get_timecount(struct timecounter *tc);
   49 
   50 static u_int32_t piix_timecounter_address;
   51 static u_int piix_freq = 14318182/4;
   52 
   53 static struct timecounter piix_timecounter = {
   54         piix_get_timecount,
   55         0,
   56         0xffffff,
   57         0,
   58         "PIIX"
   59 };
   60 
   61 SYSCTL_OPAQUE(_debug, OID_AUTO, piix_timecounter, CTLFLAG_RD,
   62         &piix_timecounter, sizeof(piix_timecounter), "S,timecounter", "");
   63 
   64 static int
   65 sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
   66 {
   67         int error;
   68         u_int freq;
   69 
   70         if (piix_timecounter.tc_frequency == 0)
   71                 return (EOPNOTSUPP);
   72         freq = piix_freq;
   73         error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
   74         if (error == 0 && req->newptr != NULL) {
   75                 piix_freq = freq;
   76                 piix_timecounter.tc_frequency = piix_freq;
   77                 update_timecounter(&piix_timecounter);
   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         switch (pci_get_devid(dev)) {
  106         case 0x71138086:
  107                 d = pci_read_config(dev, 0x4, 2);
  108                 if (!(d & 1))
  109                         return 0;       /* IO space not mapped */
  110                 d = pci_read_config(dev, 0x40, 4);
  111                 piix_timecounter_address = (d & 0xffc0) + 8;
  112                 piix_timecounter.tc_frequency = piix_freq;
  113                 init_timecounter(&piix_timecounter);
  114                 return (ENXIO);
  115         };
  116         return (ENXIO);
  117 }
  118 
  119 static int
  120 piix_attach (device_t dev)
  121 {
  122         
  123         return 0;
  124 }
  125 
  126 static device_method_t piix_methods[] = {
  127         /* Device interface */
  128         DEVMETHOD(device_probe,         piix_probe),
  129         DEVMETHOD(device_attach,        piix_attach),
  130         { 0, 0 }
  131 };
  132 
  133 static driver_t piix_driver = {
  134         "piix",
  135         piix_methods,
  136         1,
  137 };
  138 
  139 static devclass_t piix_devclass;
  140 
  141 DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);

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

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