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/*
* Count register synchronisation.
*
* All CPUs will have their count registers synchronised to the CPU0 expirelo
* 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...)
*
* FIXME: broken for SMTC
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/irqflags.h>
#include <linux/r4k-timer.h>
#include <asm/atomic.h>
#include <asm/barrier.h>
#include <asm/cpumask.h>
#include <asm/mipsregs.h>
static atomic_t __initdata count_start_flag = ATOMIC_INIT(0);
static atomic_t __initdata count_count_start = ATOMIC_INIT(0);
static atomic_t __initdata count_count_stop = ATOMIC_INIT(0);
#define COUNTON 100
#define NR_LOOPS 5
void __init synchronise_count_master(void)
{
int i;
unsigned long flags;
unsigned int initcount;
int nslaves;
#ifdef CONFIG_MIPS_MT_SMTC
/*
* SMTC needs to synchronise per VPE, not per CPU
* ignore for now
*/
return;
#endif
pr_info("Checking COUNT synchronization across %u CPUs: ",
num_online_cpus());
local_irq_save(flags);
/*
* Notify the slaves that it's time to start
*/
atomic_set(&count_start_flag, 1);
smp_wmb();
/* Count will be initialised to expirelo for all CPU's */
initcount = expirelo;
/*
* 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.
*/
nslaves = num_online_cpus()-1;
for (i = 0; i < NR_LOOPS; i++) {
/* slaves loop on '!= ncpus' */
while (atomic_read(&count_count_start) != nslaves)
mb();
atomic_set(&count_count_stop, 0);
smp_wmb();
/* this lets the slaves write their count register */
atomic_inc(&count_count_start);
/*
* Everyone initialises count in the last loop:
*/
if (i == NR_LOOPS-1)
write_c0_count(initcount);
/*
* Wait for all slaves to leave the synchronization point:
*/
while (atomic_read(&count_count_stop) != nslaves)
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
*/
printk("done.\n");
}
void __init synchronise_count_slave(void)
{
int i;
unsigned long flags;
unsigned int initcount;
int ncpus;
#ifdef CONFIG_MIPS_MT_SMTC
/*
* SMTC needs to synchronise per VPE, not per CPU
* ignore for now
*/
return;
#endif
local_irq_save(flags);
/*
* Not every cpu is online at the time this gets called,
* so we first wait for the master to say everyone is ready
*/
while (!atomic_read(&count_start_flag))
mb();
/* Count will be initialised to expirelo for all CPU's */
initcount = expirelo;
ncpus = num_online_cpus();
for (i = 0; i < NR_LOOPS; i++) {
atomic_inc(&count_count_start);
while (atomic_read(&count_count_start) != ncpus)
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) != ncpus)
mb();
}
/* Arrange for an interrupt in a short while */
write_c0_compare(read_c0_count() + COUNTON);
local_irq_restore(flags);
}
#undef NR_LOOPS
#endif
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