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 } 51