xref: /linux/arch/s390/lib/delay.c (revision f3d9478b2ce468c3115b02ecae7e975990697f15)
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