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

     /*-
      * ----------------------------------------------------------------------------
      * "THE BEER-WARE LICENSE" (Revision 42):
      * <phk@FreeBSD.ORG> wrote this file.  As long as you retain this notice you
      * can do whatever you want with this stuff. If we meet some day, and you think
      * this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
      * ----------------------------------------------------------------------------
      */
     
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/5.2/sys/i386/i386/mp_clock.c 121480 2003-10-24 21:01:31Z jhb $");
    
    /*-
     * Just when we thought life were beautiful, reality pops its grim face over
     * the edge again:
     *
     * ] 20. ACPI Timer Errata
     * ]
     * ]   Problem: The power management timer may return improper result when
     * ]   read. Although the timer value settles properly after incrementing,
     * ]   while incrementing there is a 3nS window every 69.8nS where the
     * ]   timer value is indeterminate (a 4.2% chance that the data will be
     * ]   incorrect when read). As a result, the ACPI free running count up
     * ]   timer specification is violated due to erroneous reads.  Implication:
     * ]   System hangs due to the "inaccuracy" of the timer when used by
     * ]   software for time critical events and delays.
     * ] 
     * ] Workaround: Read the register twice and compare.
     * ] Status: This will not be fixed in the PIIX4 or PIIX4E.
     *
     * The counter is in other words not latched to the PCI bus clock when
     * read.  Notice the workaround isn't:  We need to read until we have
     * three monotonic samples and then use the middle one, otherwise we are
     * not protected against the fact that the bits can be wrong in two
     * directions.  If we only cared about monosity two reads would be enough.
     */
    
    /* #include "opt_bus.h" */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/timetc.h>
    #include <sys/kernel.h>
    #include <sys/sysctl.h>
    #include <sys/bus.h>
    
    #include <dev/pci/pcireg.h>
    #include <dev/pci/pcivar.h>
    
    static unsigned piix_get_timecount(struct timecounter *tc);
    
    static u_int32_t piix_timecounter_address;
    static u_int piix_freq = 14318182/4;
    
    static struct timecounter piix_timecounter = {
            piix_get_timecount,     /* get_timecount */
            0,                      /* no poll_pps */
            0xffffff,               /* counter_mask */
            0,                      /* frequency */
            "PIIX"                  /* name */
    };
    
    
    static int
    sysctl_machdep_piix_freq(SYSCTL_HANDLER_ARGS)
    {
            int error;
            u_int freq;
    
            if (piix_timecounter.tc_frequency == 0)
                    return (EOPNOTSUPP);
            freq = piix_freq;
            error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
            if (error == 0 && req->newptr != NULL) {
                    piix_freq = freq;
                    piix_timecounter.tc_frequency = piix_freq;
            }
            return (error);
    }
    
    SYSCTL_PROC(_machdep, OID_AUTO, piix_freq, CTLTYPE_INT | CTLFLAG_RW,
        0, sizeof(u_int), sysctl_machdep_piix_freq, "I", "");
    
    static unsigned
    piix_get_timecount(struct timecounter *tc)
    {
            unsigned u1, u2, u3;
    
            u2 = inl(piix_timecounter_address);
            u3 = inl(piix_timecounter_address);
            do {
                    u1 = u2;
                    u2 = u3;
                    u3 = inl(piix_timecounter_address);
            } while (u1 > u2 || u2 > u3);
            return (u2);
    }
    
    static int
   piix_probe(device_t dev)
   {
           u_int32_t d;
   
           if (devclass_get_device(devclass_find("acpi"), 0) != NULL)
                   return (ENXIO);
           switch (pci_get_devid(dev)) {
           case 0x71138086:
                   device_set_desc(dev, "PIIX Timecounter");
                   break;
           default:
                   return (ENXIO);
           }
   
           d = pci_read_config(dev, PCIR_COMMAND, 2);
           if (!(d & PCIM_CMD_PORTEN)) {
                   device_printf(dev, "PIIX I/O space not mapped\n");
                   return (ENXIO);
           }
           return (0);
   }
   
   static int
   piix_attach(device_t dev)
   {
           u_int32_t d;
   
           d = pci_read_config(dev, 0x40, 4);
           piix_timecounter_address = (d & 0xffc0) + 8;
           piix_timecounter.tc_frequency = piix_freq;
           tc_init(&piix_timecounter);
           return (0);
   }
   
   static device_method_t piix_methods[] = {
           /* Device interface */
           DEVMETHOD(device_probe,         piix_probe),
           DEVMETHOD(device_attach,        piix_attach),
           { 0, 0 }
   };
   
   static driver_t piix_driver = {
           "piix",
           piix_methods,
           1,
   };
   
   static devclass_t piix_devclass;
   
   DRIVER_MODULE(piix, pci, piix_driver, piix_devclass, 0, 0);

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