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/*
*
* Copyright (C) 2018 Google LLC
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <libpayload.h>
#include <arch/apic.h>
/* The pause instruction can delay 10-140 CPU cycles, so avoid calling it when
* getting close to finishing. Depending on the timer source, the timer can be
* running at CPU frequency, bus frequency, or some arbitrary value. We assume
* that the timer is running at the CPU frequency. */
#define PAUSE_THRESHOLD_TICKS 150
/* Let's assume APIC interrupts take at least 100us */
#define APIC_INTERRUPT_LATENCY_NS (100 * NSECS_PER_USEC)
void arch_ndelay(uint64_t ns)
{
uint64_t delta = ns * timer_hz() / NSECS_PER_SEC;
uint64_t pause_delta = 0;
uint64_t apic_us = 0;
uint64_t start = timer_raw_value();
if (ns > APIC_INTERRUPT_LATENCY_NS)
apic_us = (ns - APIC_INTERRUPT_LATENCY_NS) / NSECS_PER_USEC;
if (CONFIG(LP_ENABLE_APIC) && apic_initialized() && apic_us)
apic_delay(apic_us);
if (delta > PAUSE_THRESHOLD_TICKS)
pause_delta = delta - PAUSE_THRESHOLD_TICKS;
while (timer_raw_value() - start < pause_delta)
asm volatile("pause\n\t");
while (timer_raw_value() - start < delta)
continue;
}
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