text: // SPDX-License-Identifier: GPL-2.0
  /*
   *	Precise Delay Loops for parisc
   *
   *	based on code by:
   *	Copyright (C) 1993 Linus Torvalds
   *	Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
   *	Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com>
   *
   *	parisc implementation:
   *	Copyright (C) 2013 Helge Deller <deller@gmx.de>
   */
  
  
  #include <linux/module.h>
  #include <linux/preempt.h>
  #include <linux/init.h>
  
  #include <asm/delay.h>
  #include <asm/special_insns.h>    /* for mfctl() */
  #include <asm/processor.h> /* for boot_cpu_data */
  
  /* CR16 based delay: */
  static void __cr16_delay(unsigned long __loops)
  {
  	/*
  	 * Note: Due to unsigned math, cr16 rollovers shouldn't be
  	 * a problem here. However, on 32 bit, we need to make sure
  	 * we don't pass in too big a value. The current default
  	 * value of MAX_UDELAY_MS should help prevent this.
  	 */
  	u32 bclock, now, loops = __loops;
  	int cpu;
  
  	preempt_disable();
  	cpu = smp_processor_id();
  	bclock = mfctl(16);
  	for (;;) {
  		now = mfctl(16);
  		if ((now - bclock) >= loops)
  			break;
  
  		/* Allow RT tasks to run */
  		preempt_enable();
  		asm volatile("	nop\n");
  		barrier();
  		preempt_disable();
  
  		/*
  		 * It is possible that we moved to another CPU, and
  		 * since CR16's are per-cpu we need to calculate
  		 * that. The delay must guarantee that we wait "at
  		 * least" the amount of time. Being moved to another
  		 * CPU could make the wait longer but we just need to
  		 * make sure we waited long enough. Rebalance the
  		 * counter for this CPU.
  		 */
  		if (unlikely(cpu != smp_processor_id())) {
  			loops -= (now - bclock);
  			cpu = smp_processor_id();
  			bclock = mfctl(16);
  		}
  	}
  	preempt_enable();
  }
  
  
  void __udelay(unsigned long usecs)
  {
  	__cr16_delay(usecs * ((unsigned long)boot_cpu_data.cpu_hz / 1000000UL));
  }
  EXPORT_SYMBOL(__udelay);
  