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/config.h> 15 #include <linux/sched.h> 16 #include <linux/delay.h> 17 18 #ifdef CONFIG_SMP 19 #include <asm/smp.h> 20 #endif 21 22 void __delay(unsigned long loops) 23 { 24 /* 25 * To end the bloody studid and useless discussion about the 26 * BogoMips number I took the liberty to define the __delay 27 * function in a way that that resulting BogoMips number will 28 * yield the megahertz number of the cpu. The important function 29 * is udelay and that is done using the tod clock. -- martin. 30 */ 31 __asm__ __volatile__( 32 "0: brct %0,0b" 33 : /* no outputs */ : "r" ((loops/2) + 1)); 34 } 35 36 /* 37 * Waits for 'usecs' microseconds using the tod clock, giving up the time slice 38 * of the virtual PU inbetween to avoid congestion. 39 */ 40 void __udelay(unsigned long usecs) 41 { 42 uint64_t start_cc, end_cc; 43 44 if (usecs == 0) 45 return; 46 asm volatile ("STCK %0" : "=m" (start_cc)); 47 do { 48 cpu_relax(); 49 asm volatile ("STCK %0" : "=m" (end_cc)); 50 } while (((end_cc - start_cc)/4096) < usecs); 51 } 52