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/*
* Count register synchronisation.
*
* All CPUs will have their count registers synchronised to the CPU0 next time
* value. This can cause a small timewarp for CPU0. All other CPU's should
* not have done anything significant (but they may have had interrupts
* enabled briefly - prom_smp_finish() should not be responsible for enabling
* interrupts...)
*/
#include <linux/kernel.h>
#include <linux/irqflags.h>
#include <linux/cpumask.h>
#include <asm/r4k-timer.h>
#include <linux/atomic.h>
#include <asm/barrier.h>
#include <asm/mipsregs.h>
static unsigned int initcount = 0;
static atomic_t count_count_start = ATOMIC_INIT(0);
static atomic_t count_count_stop = ATOMIC_INIT(0);
#define COUNTON 100
#define NR_LOOPS 3
void synchronise_count_master(int cpu)
{
int i;
unsigned long flags;
pr_info("Synchronize counters for CPU %u: ", cpu);
local_irq_save(flags);
/*
* We loop a few times to get a primed instruction cache,
* then the last pass is more or less synchronised and
* the master and slaves each set their cycle counters to a known
* value all at once. This reduces the chance of having random offsets
* between the processors, and guarantees that the maximum
* delay between the cycle counters is never bigger than
* the latency of information-passing (cachelines) between
* two CPUs.
*/
for (i = 0; i < NR_LOOPS; i++) {
/* slaves loop on '!= 2' */
while (atomic_read(&count_count_start) != 1)
mb();
atomic_set(&count_count_stop, 0);
smp_wmb();
/* Let the slave writes its count register */
atomic_inc(&count_count_start);
/* Count will be initialised to current timer */
if (i == 1)
initcount = read_c0_count();
/*
* Everyone initialises count in the last loop:
*/
if (i == NR_LOOPS-1)
write_c0_count(initcount);
/*
* Wait for slave to leave the synchronization point:
*/
while (atomic_read(&count_count_stop) != 1)
mb();
atomic_set(&count_count_start, 0);
smp_wmb();
atomic_inc(&count_count_stop);
}
/* Arrange for an interrupt in a short while */
write_c0_compare(read_c0_count() + COUNTON);
local_irq_restore(flags);
/*
* i386 code reported the skew here, but the
* count registers were almost certainly out of sync
* so no point in alarming people
*/
pr_cont("done.\n");
}
void synchronise_count_slave(int cpu)
{
int i;
/*
* Not every cpu is online at the time this gets called,
* so we first wait for the master to say everyone is ready
*/
for (i = 0; i < NR_LOOPS; i++) {
atomic_inc(&count_count_start);
while (atomic_read(&count_count_start) != 2)
mb();
/*
* Everyone initialises count in the last loop:
*/
if (i == NR_LOOPS-1)
write_c0_count(initcount);
atomic_inc(&count_count_stop);
while (atomic_read(&count_count_stop) != 2)
mb();
}
/* Arrange for an interrupt in a short while */
write_c0_compare(read_c0_count() + COUNTON);
}
#undef NR_LOOPS
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