112 lines
3.2 KiB
C
112 lines
3.2 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Emulate a local clock event device via a pseudo clock device.
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*/
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#include <linux/cpu.h>
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#include <linux/err.h>
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#include <linux/hrtimer.h>
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#include <linux/interrupt.h>
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#include <linux/percpu.h>
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#include <linux/profile.h>
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#include <linux/clockchips.h>
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#include <linux/sched.h>
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#include <linux/smp.h>
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#include <linux/module.h>
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#include "tick-internal.h"
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static struct hrtimer bctimer;
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static int bc_shutdown(struct clock_event_device *evt)
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{
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/*
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* Note, we cannot cancel the timer here as we might
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* run into the following live lock scenario:
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*
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* cpu 0 cpu1
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* lock(broadcast_lock);
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* hrtimer_interrupt()
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* bc_handler()
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* tick_handle_oneshot_broadcast();
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* lock(broadcast_lock);
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* hrtimer_cancel()
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* wait_for_callback()
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*/
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hrtimer_try_to_cancel(&bctimer);
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return 0;
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}
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/*
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* This is called from the guts of the broadcast code when the cpu
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* which is about to enter idle has the earliest broadcast timer event.
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*/
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static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
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{
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/*
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* This is called either from enter/exit idle code or from the
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* broadcast handler. In all cases tick_broadcast_lock is held.
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*
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* hrtimer_cancel() cannot be called here neither from the
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* broadcast handler nor from the enter/exit idle code. The idle
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* code can run into the problem described in bc_shutdown() and the
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* broadcast handler cannot wait for itself to complete for obvious
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* reasons.
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*
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* Each caller tries to arm the hrtimer on its own CPU, but if the
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* hrtimer callbback function is currently running, then
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* hrtimer_start() cannot move it and the timer stays on the CPU on
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* which it is assigned at the moment.
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*
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* As this can be called from idle code, the hrtimer_start()
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* invocation has to be wrapped with RCU_NONIDLE() as
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* hrtimer_start() can call into tracing.
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*/
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RCU_NONIDLE( {
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hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED_HARD);
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/*
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* The core tick broadcast mode expects bc->bound_on to be set
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* correctly to prevent a CPU which has the broadcast hrtimer
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* armed from going deep idle.
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*
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* As tick_broadcast_lock is held, nothing can change the cpu
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* base which was just established in hrtimer_start() above. So
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* the below access is safe even without holding the hrtimer
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* base lock.
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*/
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bc->bound_on = bctimer.base->cpu_base->cpu;
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} );
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return 0;
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}
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static struct clock_event_device ce_broadcast_hrtimer = {
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.name = "bc_hrtimer",
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.set_state_shutdown = bc_shutdown,
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.set_next_ktime = bc_set_next,
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.features = CLOCK_EVT_FEAT_ONESHOT |
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CLOCK_EVT_FEAT_KTIME |
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CLOCK_EVT_FEAT_HRTIMER,
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.rating = 0,
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.bound_on = -1,
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.min_delta_ns = 1,
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.max_delta_ns = KTIME_MAX,
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.min_delta_ticks = 1,
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.max_delta_ticks = ULONG_MAX,
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.mult = 1,
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.shift = 0,
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.cpumask = cpu_possible_mask,
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};
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static enum hrtimer_restart bc_handler(struct hrtimer *t)
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{
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ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
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return HRTIMER_NORESTART;
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}
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void tick_setup_hrtimer_broadcast(void)
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{
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hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
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bctimer.function = bc_handler;
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clockevents_register_device(&ce_broadcast_hrtimer);
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}
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