arch/s390/lib/delay.c

   1 /*
   2  *  arch/s390/kernel/delay.c
   3  *    Precise Delay Loops for S390
   4  *
   5  *  S390 version
   6  *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
   7  *    Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com),
   8  *
   9  *  Derived from "arch/i386/lib/delay.c"
  10  *    Copyright (C) 1993 Linus Torvalds
  11  *    Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
  12  */
  13
  14 #include <linux/sched.h>
  15 #include <linux/delay.h>
  16
  17 #ifdef CONFIG_SMP
  18 #include <asm/smp.h>
  19 #endif
  20
  21 void __delay(unsigned long loops)
  22 {
  23         /*
  24          * To end the bloody studid and useless discussion about the
  25          * BogoMips number I took the liberty to define the __delay
  26          * function in a way that that resulting BogoMips number will
  27          * yield the megahertz number of the cpu. The important function
  28          * is udelay and that is done using the tod clock. -- martin.
  29          */
  30         __asm__ __volatile__(
  31                 "0: brct %0,0b"
  32                 : /* no outputs */ : "r" ((loops/2) + 1));
  33 }
  34
  35 /*
  36  * Waits for 'usecs' microseconds using the tod clock, giving up the time slice
  37  * of the virtual PU inbetween to avoid congestion.
  38  */
  39 void __udelay(unsigned long usecs)
  40 {
  41         uint64_t start_cc, end_cc;
  42
  43         if (usecs == 0)
  44                 return;
  45         asm volatile ("STCK %0" : "=m" (start_cc));
  46         do {
  47                 cpu_relax();
  48                 asm volatile ("STCK %0" : "=m" (end_cc));
  49         } while (((end_cc - start_cc)/4096) < usecs);
  50 }