2 * Precise Delay Loops for i386
4 * Copyright (C) 1993 Linus Torvalds
5 * Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
6 * Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
8 * The __delay function must _NOT_ be inlined as its execution time
9 * depends wildly on alignment on many x86 processors. The additional
10 * jump magic is needed to get the timing stable on all the CPU's
11 * we have to worry about.
14 #include <linux/module.h>
15 #include <linux/sched.h>
16 #include <linux/timex.h>
17 #include <linux/preempt.h>
18 #include <linux/delay.h>
19 #include <linux/init.h>
21 #include <asm/processor.h>
22 #include <asm/delay.h>
23 #include <asm/timer.h>
29 /* simple loop based delay: */
30 static void delay_loop(unsigned long loops
)
45 : /* we don't need output */
50 /* TSC based delay: */
51 static void delay_tsc(unsigned long __loops
)
53 u32 bclock
, now
, loops
= __loops
;
57 cpu
= smp_processor_id();
63 if ((now
- bclock
) >= loops
)
66 /* Allow RT tasks to run */
72 * It is possible that we moved to another CPU, and
73 * since TSC's are per-cpu we need to calculate
74 * that. The delay must guarantee that we wait "at
75 * least" the amount of time. Being moved to another
76 * CPU could make the wait longer but we just need to
77 * make sure we waited long enough. Rebalance the
78 * counter for this CPU.
80 if (unlikely(cpu
!= smp_processor_id())) {
81 loops
-= (now
- bclock
);
82 cpu
= smp_processor_id();
91 * Since we calibrate only once at boot, this
92 * function should be set once at boot and not changed
94 static void (*delay_fn
)(unsigned long) = delay_loop
;
96 void use_tsc_delay(void)
101 int __devinit
read_current_timer(unsigned long *timer_val
)
103 if (delay_fn
== delay_tsc
) {
110 void __delay(unsigned long loops
)
114 EXPORT_SYMBOL(__delay
);
116 inline void __const_udelay(unsigned long xloops
)
122 :"=d" (xloops
), "=&a" (d0
)
124 (this_cpu_read(cpu_info
.loops_per_jiffy
) * (HZ
/4)));
128 EXPORT_SYMBOL(__const_udelay
);
130 void __udelay(unsigned long usecs
)
132 __const_udelay(usecs
* 0x000010c7); /* 2**32 / 1000000 (rounded up) */
134 EXPORT_SYMBOL(__udelay
);
136 void __ndelay(unsigned long nsecs
)
138 __const_udelay(nsecs
* 0x00005); /* 2**32 / 1000000000 (rounded up) */
140 EXPORT_SYMBOL(__ndelay
);