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Diffstat (limited to 'arch/mips/kernel/cevt-smtc.c')
| -rw-r--r-- | arch/mips/kernel/cevt-smtc.c | 321 |
1 files changed, 321 insertions, 0 deletions
diff --git a/arch/mips/kernel/cevt-smtc.c b/arch/mips/kernel/cevt-smtc.c new file mode 100644 index 00000000000..5162fe4b595 --- /dev/null +++ b/arch/mips/kernel/cevt-smtc.c @@ -0,0 +1,321 @@ +/* + * 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 <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 = 0L; + unsigned long reference; + + +repeat: + 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 mips_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(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; +} |