delay.c

/*
 *    Precise Delay Loops for S390
 *
 *    Copyright IBM Corp. 1999,2008
 *    Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>,
 *		 Heiko Carstens <heiko.carstens@de.ibm.com>,
 */

#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/timex.h>
#include <linux/module.h>
#include <linux/irqflags.h>
#include <linux/interrupt.h>

void __delay(unsigned long loops)
{
        /*
         * To end the bloody studid and useless discussion about the
         * BogoMips number I took the liberty to define the __delay
         * function in a way that that resulting BogoMips number will
         * yield the megahertz number of the cpu. The important function
         * is udelay and that is done using the tod clock. -- martin.
         */
	asm volatile("0: brct %0,0b" : : "d" ((loops/2) + 1));
}

static void __udelay_disabled(unsigned long usecs)
{
	unsigned long mask, cr0, cr0_saved;
	u64 clock_saved;

	clock_saved = local_tick_disable();
	set_clock_comparator(get_clock() + ((u64) usecs << 12));
	__ctl_store(cr0_saved, 0, 0);
	cr0 = (cr0_saved & 0xffff00e0) | 0x00000800;
	__ctl_load(cr0 , 0, 0);
	mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_EXT;
	lockdep_off();
	trace_hardirqs_on();
	__load_psw_mask(mask);
	local_irq_disable();
	lockdep_on();
	__ctl_load(cr0_saved, 0, 0);
	local_tick_enable(clock_saved);
	set_clock_comparator(S390_lowcore.clock_comparator);
}

static void __udelay_enabled(unsigned long usecs)
{
	unsigned long mask;
	u64 clock_saved;
	u64 end;

	mask = psw_kernel_bits | PSW_MASK_WAIT | PSW_MASK_EXT | PSW_MASK_IO;
	end = get_clock() + ((u64) usecs << 12);
	do {
		clock_saved = 0;
		if (end < S390_lowcore.clock_comparator) {
			clock_saved = local_tick_disable();
			set_clock_comparator(end);
		}
		trace_hardirqs_on();
		__load_psw_mask(mask);
		local_irq_disable();
		if (clock_saved)
			local_tick_enable(clock_saved);
	} while (get_clock() < end);
	set_clock_comparator(S390_lowcore.clock_comparator);
}

/*
 * Waits for 'usecs' microseconds using the TOD clock comparator.
 */
void __udelay(unsigned long usecs)
{
	unsigned long flags;

	preempt_disable();
	local_irq_save(flags);
	if (in_irq()) {
		__udelay_disabled(usecs);
		goto out;
	}
	if (in_softirq()) {
		if (raw_irqs_disabled_flags(flags))
			__udelay_disabled(usecs);
		else
			__udelay_enabled(usecs);
		goto out;
	}
	if (raw_irqs_disabled_flags(flags)) {
		local_bh_disable();
		__udelay_disabled(usecs);
		_local_bh_enable();
		goto out;
	}
	__udelay_enabled(usecs);
out:
	local_irq_restore(flags);
	preempt_enable();
}
EXPORT_SYMBOL(__udelay);

/*
 * Simple udelay variant. To be used on startup and reboot
 * when the interrupt handler isn't working.
 */
void udelay_simple(unsigned long usecs)
{
	u64 end;

	end = get_clock() + ((u64) usecs << 12);
	while (get_clock() < end)
		cpu_relax();
}