kernel-hacking-2024-linux-steffo/arch/arc/kernel/time.c

/*
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * vineetg: Jan 1011
 *  -sched_clock( ) no longer jiffies based. Uses the same clocksource
 *   as gtod
 *
 * Rajeshwarr/Vineetg: Mar 2008
 *  -Implemented CONFIG_GENERIC_TIME (rather deleted arch specific code)
 *   for arch independent gettimeofday()
 *  -Implemented CONFIG_GENERIC_CLOCKEVENTS as base for hrtimers
 *
 * Vineetg: Mar 2008: Forked off from time.c which now is time-jiff.c
 */

/* ARC700 has two 32bit independent prog Timers: TIMER0 and TIMER1
 * Each can programmed to go from @count to @limit and optionally
 * interrupt when that happens.
 * A write to Control Register clears the Interrupt
 *
 * We've designated TIMER0 for events (clockevents)
 * while TIMER1 for free running (clocksource)
 *
 * Newer ARC700 cores have 64bit clk fetching RTSC insn, preferred over TIMER1
 */

#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/profile.h>
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <asm/irq.h>
#include <asm/arcregs.h>
#include <asm/clk.h>
#include <asm/mach_desc.h>

#define ARC_TIMER_MAX	0xFFFFFFFF

/********** Clock Source Device *********/

#ifdef CONFIG_ARC_HAS_RTSC

int __cpuinit arc_counter_setup(void)
{
	/* RTSC insn taps into cpu clk, needs no setup */

	/* For SMP, only allowed if cross-core-sync, hence usable as cs */
	return 1;
}

static cycle_t arc_counter_read(struct clocksource *cs)
{
	unsigned long flags;
	union {
#ifdef CONFIG_CPU_BIG_ENDIAN
		struct { u32 high, low; };
#else
		struct { u32 low, high; };
#endif
		cycle_t  full;
	} stamp;

	flags = arch_local_irq_save();

	__asm__ __volatile(
	"	.extCoreRegister tsch, 58,  r, cannot_shortcut	\n"
	"	rtsc %0, 0	\n"
	"	mov  %1, tsch	\n"	/* TSCH is extn core reg 58 */
	: "=r" (stamp.low), "=r" (stamp.high));

	arch_local_irq_restore(flags);

	return stamp.full;
}

static struct clocksource arc_counter = {
	.name   = "ARC RTSC",
	.rating = 300,
	.read   = arc_counter_read,
	.mask   = CLOCKSOURCE_MASK(64),
	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
};

#else /* !CONFIG_ARC_HAS_RTSC */

static bool is_usable_as_clocksource(void)
{
#ifdef CONFIG_SMP
	return 0;
#else
	return 1;
#endif
}

/*
 * set 32bit TIMER1 to keep counting monotonically and wraparound
 */
int __cpuinit arc_counter_setup(void)
{
	write_aux_reg(ARC_REG_TIMER1_LIMIT, ARC_TIMER_MAX);
	write_aux_reg(ARC_REG_TIMER1_CNT, 0);
	write_aux_reg(ARC_REG_TIMER1_CTRL, TIMER_CTRL_NH);

	return is_usable_as_clocksource();
}

static cycle_t arc_counter_read(struct clocksource *cs)
{
	return (cycle_t) read_aux_reg(ARC_REG_TIMER1_CNT);
}

static struct clocksource arc_counter = {
	.name   = "ARC Timer1",
	.rating = 300,
	.read   = arc_counter_read,
	.mask   = CLOCKSOURCE_MASK(32),
	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
};

#endif

/********** Clock Event Device *********/

/*
 * Arm the timer to interrupt after @limit cycles
 * The distinction for oneshot/periodic is done in arc_event_timer_ack() below
 */
static void arc_timer_event_setup(unsigned int limit)
{
	write_aux_reg(ARC_REG_TIMER0_LIMIT, limit);
	write_aux_reg(ARC_REG_TIMER0_CNT, 0);	/* start from 0 */

	write_aux_reg(ARC_REG_TIMER0_CTRL, TIMER_CTRL_IE | TIMER_CTRL_NH);
}

/*
 * Acknowledge the interrupt (oneshot) and optionally re-arm it (periodic)
 * -Any write to CTRL Reg will ack the intr (NH bit: Count when not halted)
 * -Rearming is done by setting the IE bit
 *
 * Small optimisation: Normal code would have been
 *   if (irq_reenable)
 *     CTRL_REG = (IE | NH);
 *   else
 *     CTRL_REG = NH;
 * However since IE is BIT0 we can fold the branch
 */
static void arc_timer_event_ack(unsigned int irq_reenable)
{
	write_aux_reg(ARC_REG_TIMER0_CTRL, irq_reenable | TIMER_CTRL_NH);
}

static int arc_clkevent_set_next_event(unsigned long delta,
				       struct clock_event_device *dev)
{
	arc_timer_event_setup(delta);
	return 0;
}

static void arc_clkevent_set_mode(enum clock_event_mode mode,
				  struct clock_event_device *dev)
{
	switch (mode) {
	case CLOCK_EVT_MODE_PERIODIC:
		arc_timer_event_setup(arc_get_core_freq() / HZ);
		break;
	case CLOCK_EVT_MODE_ONESHOT:
		break;
	default:
		break;
	}

	return;
}

static DEFINE_PER_CPU(struct clock_event_device, arc_clockevent_device) = {
	.name		= "ARC Timer0",
	.features	= CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC,
	.mode		= CLOCK_EVT_MODE_UNUSED,
	.rating		= 300,
	.irq		= TIMER0_IRQ,	/* hardwired, no need for resources */
	.set_next_event = arc_clkevent_set_next_event,
	.set_mode	= arc_clkevent_set_mode,
};

static irqreturn_t timer_irq_handler(int irq, void *dev_id)
{
	struct clock_event_device *clk = &__get_cpu_var(arc_clockevent_device);

	arc_timer_event_ack(clk->mode == CLOCK_EVT_MODE_PERIODIC);
	clk->event_handler(clk);
	return IRQ_HANDLED;
}

static struct irqaction arc_timer_irq = {
	.name    = "Timer0 (clock-evt-dev)",
	.flags   = IRQF_TIMER | IRQF_PERCPU,
	.handler = timer_irq_handler,
};

/*
 * Setup the local event timer for @cpu
 * N.B. weak so that some exotic ARC SoCs can completely override it
 */
void __attribute__((weak)) __cpuinit arc_local_timer_setup(unsigned int cpu)
{
	struct clock_event_device *clk = &per_cpu(arc_clockevent_device, cpu);

	clockevents_calc_mult_shift(clk, arc_get_core_freq(), 5);

	clk->max_delta_ns = clockevent_delta2ns(ARC_TIMER_MAX, clk);
	clk->cpumask = cpumask_of(cpu);

	clockevents_register_device(clk);

	/*
	 * setup the per-cpu timer IRQ handler - for all cpus
	 * For non boot CPU explicitly unmask at intc
	 * setup_irq() -> .. -> irq_startup() already does this on boot-cpu
	 */
	if (!cpu)
		setup_irq(TIMER0_IRQ, &arc_timer_irq);
	else
		arch_unmask_irq(TIMER0_IRQ);
}

/*
 * Called from start_kernel() - boot CPU only
 *
 * -Sets up h/w timers as applicable on boot cpu
 * -Also sets up any global state needed for timer subsystem:
 *    - for "counting" timer, registers a clocksource, usable across CPUs
 *      (provided that underlying counter h/w is synchronized across cores)
 *    - for "event" timer, sets up TIMER0 IRQ (as that is platform agnostic)
 */
void __init time_init(void)
{
	/*
	 * sets up the timekeeping free-flowing counter which also returns
	 * whether the counter is usable as clocksource
	 */
	if (arc_counter_setup())
		/*
		 * CLK upto 4.29 GHz can be safely represented in 32 bits
		 * because Max 32 bit number is 4,294,967,295
		 */
		clocksource_register_hz(&arc_counter, arc_get_core_freq());

	/* sets up the periodic event timer */
	arc_local_timer_setup(smp_processor_id());

	if (machine_desc->init_time)
		machine_desc->init_time();
}

#ifdef CONFIG_ARC_HAS_RTSC
/*
 * sched_clock math assist
 * ns = cycles * (ns_per_sec / cpu_freq_hz)
 * ns = cycles * (10^6 / cpu_freq_khz)
 * ns = cycles * (10^6 * 2^SF / cpu_freq_khz) / 2^SF
 * ns = cycles * cyc2ns_scale >> SF
 */
#define CYC2NS_SF	10  /* 2^10, carefully chosen */
#define CYC2NS_SCALE	((1000000 << CYC2NS_SF) / (arc_get_core_freq() / 1000))

static unsigned long long cycles2ns(unsigned long long cyc)
{
	return (cyc * CYC2NS_SCALE ) >> CYC2NS_SF;
}

/*
 * Scheduler clock - a monotonically increasing clock in nanosec units.
 * It's return value must NOT wrap around.
 *
 * - Since 32bit TIMER1 will overflow almost immediately (53sec @ 80MHz), it
 *   can't be used directly.
 * - Using getrawmonotonic (TIMER1 based, but with state for last + current
 *   snapshots), is no-good either because of seqlock deadlock possibilities
 * - So only with native 64bit timer we do this, otherwise fallback to generic
 *   jiffies based version - which despite not being fine grained gaurantees
 *   the monotonically increasing semantics.
 */
unsigned long long sched_clock(void)
{
	return cycles2ns(arc_counter_read(NULL));
}
#endif