/* * 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 * Copyright (C) 2008 Kevin D. Kissell, Paralogos sarl */ #include #include #include #include #include #include #include /* * 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; }