/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 2007 MIPS Technologies, Inc.
* Copyright (C) 2007 Ralf Baechle <ralf@linux-mips.org>
* Copyright (C) 2008 Kevin D. Kissell, Paralogos sarl
*/
#include <linux/clockchips.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/smp.h>
#include <asm/smtc_ipi.h>
#include <asm/time.h>
#include <asm/cevt-r4k.h>
/*
* Variant clock event timer support for SMTC on MIPS 34K, 1004K
* or other MIPS MT cores.
*
* Notes on SMTC Support:
*
* SMTC has multiple microthread TCs pretending to be Linux CPUs.
* But there's only one Count/Compare pair per VPE, and Compare
* interrupts are taken opportunisitically by available TCs
* bound to the VPE with the Count register. The new timer
* framework provides for global broadcasts, but we really
* want VPE-level multicasts for best behavior. So instead
* of invoking the high-level clock-event broadcast code,
* this version of SMTC support uses the historical SMTC
* multicast mechanisms "under the hood", appearing to the
* generic clock layer as if the interrupts are per-CPU.
*
* The approach taken here is to maintain a set of NR_CPUS
* virtual timers, and track which "CPU" needs to be alerted
* at each event.
*
* It's unlikely that we'll see a MIPS MT core with more than
* 2 VPEs, but we *know* that we won't need to handle more
* VPEs than we have "CPUs". So NCPUs arrays of NCPUs elements
* is always going to be overkill, but always going to be enough.
*/
unsigned long smtc_nexttime[NR_CPUS][NR_CPUS];
static int smtc_nextinvpe[NR_CPUS];
/*
* Timestamps stored are absolute values to be programmed
* into Count register. Valid timestamps will never be zero.
* If a Zero Count value is actually calculated, it is converted
* to be a 1, which will introduce 1 or two CPU cycles of error
* roughly once every four billion events, which at 1000 HZ means
* about once every 50 days. If that's actually a problem, one
* could alternate squashing 0 to 1 and to -1.
*/
#define MAKEVALID(x) (((x) == 0L) ? 1L : (x))
#define ISVALID(x) ((x) != 0L)
/*
* Time comparison is subtle, as it's really truncated
* modular arithmetic.
*/
#define IS_SOONER(a, b, reference) \
(((a) - (unsigned long)(reference)) < ((b) - (unsigned long)(reference)))
/*
* CATCHUP_INCREMENT, used when the function falls behind the counter.
* Could be an increasing function instead of a constant;
*/
#define CATCHUP_INCREMENT 64
static int mips_next_event(unsigned long delta,
struct clock_event_device *evt)
{
unsigned long flags;
unsigned int mtflags;
unsigned long timestamp, reference, previous;
unsigned long nextcomp = 0L;
int vpe = current_cpu_data.vpe_id;
int cpu = smp_processor_id();
local_irq_save(flags);
mtflags = dmt();
/*
* Maintain the per-TC virtual timer
* and program the per-VPE shared Count register
* as appropriate here...
*/
reference = (unsigned long)read_c0_count();
timestamp = MAKEVALID(reference + delta);
/*
* To really model the clock, we have to catch the case
* where the current next-in-VPE timestamp is the old
* timestamp for the calling CPE, but the new value is
* in fact later. In that case, we have to do a full
* scan and discover the new next-in-VPE CPU id and
* timestamp.
*/
previous = smtc_nexttime[vpe][cpu];
if (cpu == smtc_nextinvpe[vpe] && ISVALID(previous)
&& IS_SOONER(previous, timestamp, reference)) {
int i;
int soonest = cpu;
/*
* Update timestamp array here, so that new
* value gets considered along with those of
* other virtual CPUs on the VPE.
*/
smtc_nexttime[vpe][cpu] = timestamp;
for_each_online_cpu(i) {
if (ISVALID(smtc_nexttime[vpe][i])
&& IS_SOONER(smtc_nexttime[vpe][i],
smtc_nexttime[vpe][soonest], reference)) {
soonest = i;
}
}
smtc_nextinvpe[vpe] = soonest;
nextcomp = smtc_nexttime[vpe][soonest];
/*
* Otherwise, we don't have to process the whole array rank,
* we just have to see if the event horizon has gotten closer.
*/
} else {
if (!ISVALID(smtc_nexttime[vpe][smtc_nextinvpe[vpe]]) ||
IS_SOONER(timestamp,
smtc_nexttime[vpe][smtc_nextinvpe[vpe]], reference)) {
smtc_nextinvpe[vpe] = cpu;
nextcomp = timestamp;
}
/*
* Since next-in-VPE may me the same as the executing
* virtual CPU, we update the array *after* checking
* its value.
*/
smtc_nexttime[vpe][cpu] = timestamp;
}
/*
* It may be that, in fact, we don't need to update Compare,
* but if we do, we want to make sure we didn't fall into
* a crack just behind Count.
*/
if (ISVALID(nextcomp)) {
write_c0_compare(nextcomp);
ehb();
/*
* We never return an error, we just make sure
* that we trigger the handlers as quickly as
* we can if we fell behind.
*/
while ((nextcomp - (unsigned long)read_c0_count())
> (unsigned long)LONG_MAX) {
nextcomp += CATCHUP_INCREMENT;
write_c0_compare(nextcomp);
ehb();
}
}
emt(mtflags);
local_irq_restore(flags);
return 0;
}
void smtc_distribute_timer(int vpe)
{
unsigned long flags;
unsigned int mtflags;
int cpu;
struct clock_event_device *cd;
unsigned long nextstamp;
unsigned long reference;
repeat:
nextstamp = 0L;
for_each_online_cpu(cpu) {
/*
* Find virtual CPUs within the current VPE who have
* unserviced timer requests whose time is now past.
*/
local_irq_save(flags);
mtflags = dmt();
if (cpu_data[cpu].vpe_id == vpe &&
ISVALID(smtc_nexttime[vpe][cpu])) {
reference = (unsigned long)read_c0_count();
if ((smtc_nexttime[vpe][cpu] - reference)
> (unsigned long)LONG_MAX) {
smtc_nexttime[vpe][cpu] = 0L;
emt(mtflags);
local_irq_restore(flags);
/*
* We don't send IPIs to ourself.
*/
if (cpu != smp_processor_id()) {
smtc_send_ipi(cpu, SMTC_CLOCK_TICK, 0);
} else {
cd = &per_cpu(mips_clockevent_device, cpu);
cd->event_handler(cd);
}
} else {
/* Local to VPE but Valid Time not yet reached. */
if (!ISVALID(nextstamp) ||
IS_SOONER(smtc_nexttime[vpe][cpu], nextstamp,
reference)) {
smtc_nextinvpe[vpe] = cpu;
nextstamp = smtc_nexttime[vpe][cpu];
}
emt(mtflags);
local_irq_restore(flags);
}
} else {
emt(mtflags);
local_irq_restore(flags);
}
}
/* Reprogram for interrupt at next soonest timestamp for VPE */
if (ISVALID(nextstamp)) {
write_c0_compare(nextstamp);
ehb();
if ((nextstamp - (unsigned long)read_c0_count())
> (unsigned long)LONG_MAX)
goto repeat;
}
}
irqreturn_t c0_compare_interrupt(int irq, void *dev_id)
{
int cpu = smp_processor_id();
/* If we're running SMTC, we've got MIPS MT and therefore MIPS32R2 */
handle_perf_irq(1);
if (read_c0_cause() & (1 << 30)) {
/* Clear Count/Compare Interrupt */
write_c0_compare(read_c0_compare());
smtc_distribute_timer(cpu_data[cpu].vpe_id);
}
return IRQ_HANDLED;
}
int __cpuinit smtc_clockevent_init(void)
{
uint64_t mips_freq = mips_hpt_frequency;
unsigned int cpu = smp_processor_id();
struct clock_event_device *cd;
unsigned int irq;
int i;
int j;
if (!cpu_has_counter || !mips_hpt_frequency)
return -ENXIO;
if (cpu == 0) {
for (i = 0; i < num_possible_cpus(); i++) {
smtc_nextinvpe[i] = 0;
for (j = 0; j < num_possible_cpus(); j++)
smtc_nexttime[i][j] = 0L;
}
/*
* SMTC also can't have the usablility test
* run by secondary TCs once Compare is in use.
*/
if (!c0_compare_int_usable())
return -ENXIO;
}
/*
* With vectored interrupts things are getting platform specific.
* get_c0_compare_int is a hook to allow a platform to return the
* interrupt number of it's liking.
*/
irq = MIPS_CPU_IRQ_BASE + cp0_compare_irq;
if (get_c0_compare_int)
irq = get_c0_compare_int();
cd = &per_cpu(mips_clockevent_device, cpu);
cd->name = "MIPS";
cd->features = CLOCK_EVT_FEAT_ONESHOT;
/* Calculate the min / max delta */
cd->mult = div_sc((unsigned long) mips_freq, NSEC_PER_SEC, 32);
cd->shift = 32;
cd->max_delta_ns = clockevent_delta2ns(0x7fffffff, cd);
cd->min_delta_ns = clockevent_delta2ns(0x300, cd);
cd->rating = 300;
cd->irq = irq;
cd->cpumask = cpumask_of(cpu);
cd->set_next_event = mips_next_event;
cd->set_mode = mips_set_clock_mode;
cd->event_handler = mips_event_handler;
clockevents_register_device(cd);
/*
* On SMTC we only want to do the data structure
* initialization and IRQ setup once.
*/
if (cpu)
return 0;
/*
* And we need the hwmask associated with the c0_compare
* vector to be initialized.
*/
irq_hwmask[irq] = (0x100 << cp0_compare_irq);
if (cp0_timer_irq_installed)
return 0;
cp0_timer_irq_installed = 1;
setup_irq(irq, &c0_compare_irqaction);
return 0;
}
