arch/parisc/lib/delay.c

   1 /*
   2  *      Precise Delay Loops for parisc
   3  *
   4  *      based on code by:
   5  *      Copyright (C) 1993 Linus Torvalds
   6  *      Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   7  *      Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
   8  *
   9  *      parisc implementation:
  10  *      Copyright (C) 2013 Helge Deller <deller@gmx.de>
  11  */
  12
  13
  14 #include <linux/module.h>
  15 #include <linux/preempt.h>
  16 #include <linux/init.h>
  17
  18 #include <asm/processor.h>
  19 #include <asm/delay.h>
  20
  21 #include <asm/special_insns.h>    /* for mfctl() */
  22 #include <asm/processor.h> /* for boot_cpu_data */
  23
  24 /* CR16 based delay: */
  25 static void __cr16_delay(unsigned long __loops)
  26 {
  27         /*
  28          * Note: Due to unsigned math, cr16 rollovers shouldn't be
  29          * a problem here. However, on 32 bit, we need to make sure
  30          * we don't pass in too big a value. The current default
  31          * value of MAX_UDELAY_MS should help prevent this.
  32          */
  33         u32 bclock, now, loops = __loops;
  34         int cpu;
  35
  36         preempt_disable();
  37         cpu = smp_processor_id();
  38         bclock = mfctl(16);
  39         for (;;) {
  40                 now = mfctl(16);
  41                 if ((now - bclock) >= loops)
  42                         break;
  43
  44                 /* Allow RT tasks to run */
  45                 preempt_enable();
  46                 asm volatile("  nop\n");
  47                 barrier();
  48                 preempt_disable();
  49
  50                 /*
  51                  * It is possible that we moved to another CPU, and
  52                  * since CR16's are per-cpu we need to calculate
  53                  * that. The delay must guarantee that we wait "at
  54                  * least" the amount of time. Being moved to another
  55                  * CPU could make the wait longer but we just need to
  56                  * make sure we waited long enough. Rebalance the
  57                  * counter for this CPU.
  58                  */
  59                 if (unlikely(cpu != smp_processor_id())) {
  60                         loops -= (now - bclock);
  61                         cpu = smp_processor_id();
  62                         bclock = mfctl(16);
  63                 }
  64         }
  65         preempt_enable();
  66 }
  67
  68
  69 void __udelay(unsigned long usecs)
  70 {
  71         __cr16_delay(usecs * ((unsigned long)boot_cpu_data.cpu_hz / 1000000UL));
  72 }
  73 EXPORT_SYMBOL(__udelay);