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/*
* Copyright (c) 2019 Intel Corporation
* SPDX-License-Identifier: Apache-2.0
*/
#include <zephyr/device.h>
#include <zephyr/drivers/timer/system_timer.h>
#include <zephyr/sys_clock.h>
#include <zephyr/spinlock.h>
#include <zephyr/drivers/interrupt_controller/loapic.h>
BUILD_ASSERT(!IS_ENABLED(CONFIG_SMP), "APIC timer doesn't support SMP");
/*
* Overview:
*
* This driver enables the local APIC as the Zephyr system timer. It supports
* both legacy ("tickful") mode as well as TICKLESS_KERNEL. The driver will
* work with any APIC that has the ARAT "always running APIC timer" feature
* (CPUID 0x06, EAX bit 2); for the more accurate sys_clock_cycle_get_32(),
* the invariant TSC feature (CPUID 0x80000007: EDX bit 8) is also required.
* (Ultimately systems with invariant TSCs should use a TSC-based driver,
* and the TSC-related parts should be stripped from this implementation.)
*
* Configuration:
*
* CONFIG_APIC_TIMER=y enables this timer driver.
* CONFIG_APIC_TIMER_IRQ=<irq> which IRQ to configure for the timer.
* CONFIG_APIC_TIMER_IRQ_PRIORITY=<p> priority for IRQ_CONNECT()
*
* CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=<hz> must contain the frequency seen
* by the local APIC timer block (before it gets to the timer divider).
*
* CONFIG_APIC_TIMER_TSC=y enables the more accurate TSC-based cycle counter
* for sys_clock_cycle_get_32(). This also requires the next options be set.
*
* CONFIG_APIC_TIMER_TSC_N=<n>
* CONFIG_APIC_TIMER_TSC_M=<m>
* When CONFIG_APIC_TIMER_TSC=y, these are set to indicate the ratio of
* the TSC frequency to CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC. This can be
* found via CPUID 0x15 (n = EBX, m = EAX) on most CPUs.
*/
/* These should be merged into include/drivers/interrupt_controller/loapic.h. */
#define DCR_DIVIDER_MASK 0x0000000F /* divider bits */
#define DCR_DIVIDER 0x0000000B /* divide by 1 */
#define LVT_MODE_MASK 0x00060000 /* timer mode bits */
#define LVT_MODE 0x00000000 /* one-shot */
/*
* CYCLES_PER_TICK must always be at least '2', otherwise MAX_TICKS
* will overflow int32_t, which is how 'ticks' are currently represented.
*/
#define CYCLES_PER_TICK \
(CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC / CONFIG_SYS_CLOCK_TICKS_PER_SEC)
BUILD_ASSERT(CYCLES_PER_TICK >= 2, "APIC timer: bad CYCLES_PER_TICK");
/* max number of ticks we can load into the timer in one shot */
#define MAX_TICKS (0xFFFFFFFFU / CYCLES_PER_TICK)
/*
* The spinlock protects all access to the local APIC timer registers,
* as well as 'total_cycles', 'last_announcement', and 'cached_icr'.
*
* One important invariant that must be observed: `total_cycles` + `cached_icr`
* is always an integral multiple of CYCLE_PER_TICK; this is, timer interrupts
* are only ever scheduled to occur at tick boundaries.
*/
static struct k_spinlock lock;
static uint64_t total_cycles;
static uint32_t cached_icr = CYCLES_PER_TICK;
#ifdef CONFIG_TICKLESS_KERNEL
static uint64_t last_announcement; /* last time we called sys_clock_announce() */
void sys_clock_set_timeout(int32_t n, bool idle)
{
ARG_UNUSED(idle);
uint32_t ccr;
int full_ticks; /* number of complete ticks we'll wait */
uint32_t full_cycles; /* full_ticks represented as cycles */
uint32_t partial_cycles; /* number of cycles to first tick boundary */
if (n < 1) {
full_ticks = 0;
} else if ((n == K_TICKS_FOREVER) || (n > MAX_TICKS)) {
full_ticks = MAX_TICKS - 1;
} else {
full_ticks = n - 1;
}
full_cycles = full_ticks * CYCLES_PER_TICK;
/*
* There's a wee race condition here. The timer may expire while
* we're busy reprogramming it; an interrupt will be queued at the
* local APIC and the ISR will be called too early, roughly right
* after we unlock, and not because the count we just programmed has
* counted down. Luckily this situation is easy to detect, which is
* why the ISR actually checks to be sure the CCR is 0 before acting.
*/
k_spinlock_key_t key = k_spin_lock(&lock);
ccr = x86_read_loapic(LOAPIC_TIMER_CCR);
total_cycles += (cached_icr - ccr);
partial_cycles = CYCLES_PER_TICK - (total_cycles % CYCLES_PER_TICK);
cached_icr = full_cycles + partial_cycles;
x86_write_loapic(LOAPIC_TIMER_ICR, cached_icr);
k_spin_unlock(&lock, key);
}
uint32_t sys_clock_elapsed(void)
{
uint32_t ccr;
uint32_t ticks;
k_spinlock_key_t key = k_spin_lock(&lock);
ccr = x86_read_loapic(LOAPIC_TIMER_CCR);
ticks = total_cycles - last_announcement;
ticks += cached_icr - ccr;
k_spin_unlock(&lock, key);
ticks /= CYCLES_PER_TICK;
return ticks;
}
static void isr(const void *arg)
{
ARG_UNUSED(arg);
uint32_t cycles;
int32_t ticks;
k_spinlock_key_t key = k_spin_lock(&lock);
/*
* If we get here and the CCR isn't zero, then this interrupt is
* stale: it was queued while sys_clock_set_timeout() was setting
* a new counter. Just ignore it. See above for more info.
*/
if (x86_read_loapic(LOAPIC_TIMER_CCR) != 0) {
k_spin_unlock(&lock, key);
return;
}
/* Restart the timer as early as possible to minimize drift... */
x86_write_loapic(LOAPIC_TIMER_ICR, MAX_TICKS * CYCLES_PER_TICK);
cycles = cached_icr;
cached_icr = MAX_TICKS * CYCLES_PER_TICK;
total_cycles += cycles;
ticks = (total_cycles - last_announcement) / CYCLES_PER_TICK;
last_announcement = total_cycles;
k_spin_unlock(&lock, key);
sys_clock_announce(ticks);
}
#else
static void isr(const void *arg)
{
ARG_UNUSED(arg);
k_spinlock_key_t key = k_spin_lock(&lock);
total_cycles += CYCLES_PER_TICK;
x86_write_loapic(LOAPIC_TIMER_ICR, cached_icr);
k_spin_unlock(&lock, key);
sys_clock_announce(1);
}
uint32_t sys_clock_elapsed(void)
{
return 0U;
}
#endif /* CONFIG_TICKLESS_KERNEL */
#ifdef CONFIG_APIC_TIMER_TSC
uint32_t sys_clock_cycle_get_32(void)
{
uint64_t tsc = z_tsc_read();
uint32_t cycles;
cycles = (tsc * CONFIG_APIC_TIMER_TSC_M) / CONFIG_APIC_TIMER_TSC_N;
return cycles;
}
#else
uint32_t sys_clock_cycle_get_32(void)
{
uint32_t ret;
uint32_t ccr;
k_spinlock_key_t key = k_spin_lock(&lock);
ccr = x86_read_loapic(LOAPIC_TIMER_CCR);
ret = total_cycles + (cached_icr - ccr);
k_spin_unlock(&lock, key);
return ret;
}
#endif
static int sys_clock_driver_init(const struct device *dev)
{
uint32_t val;
ARG_UNUSED(dev);
val = x86_read_loapic(LOAPIC_TIMER_CONFIG); /* set divider */
val &= ~DCR_DIVIDER_MASK;
val |= DCR_DIVIDER;
x86_write_loapic(LOAPIC_TIMER_CONFIG, val);
val = x86_read_loapic(LOAPIC_TIMER); /* set timer mode */
val &= ~LVT_MODE_MASK;
val |= LVT_MODE;
x86_write_loapic(LOAPIC_TIMER, val);
/* remember, wiring up the interrupt will mess with the LVT, too */
IRQ_CONNECT(CONFIG_APIC_TIMER_IRQ,
CONFIG_APIC_TIMER_IRQ_PRIORITY,
isr, 0, 0);
x86_write_loapic(LOAPIC_TIMER_ICR, cached_icr);
irq_enable(CONFIG_APIC_TIMER_IRQ);
return 0;
}
SYS_INIT(sys_clock_driver_init, PRE_KERNEL_2,
CONFIG_SYSTEM_CLOCK_INIT_PRIORITY);