acpi_timer.c

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/*
 * Copyright (C) 2018 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

#include <unistd.h>
#include <errno.h>
#include <assert.h>
#include <byteswap.h>
#include <ipxe/io.h>
#include <ipxe/acpi.h>

/** @file
 *
 * ACPI power management timer
 *
 */

/** ACPI timer frequency (fixed 3.579545MHz) */
#define ACPI_TIMER_HZ 3579545

/** ACPI timer mask
 *
 * Timers may be implemented as either 24-bit or 32-bit counters.  We
 * simplify the code by pessimistically assuming that the timer has
 * only 24 bits.
 */
#define ACPI_TIMER_MASK 0x00ffffffUL

/** Power management timer register address */
static unsigned int pm_tmr;

struct timer acpi_timer __timer ( TIMER_PREFERRED );

/**
 * Get current system time in ticks
 *
 * @ret ticks           Current time, in ticks
 */
static unsigned long acpi_currticks ( void ) {
        static unsigned long offset;
        static uint32_t prev;
        uint32_t now;

        /* Read timer and account for wraparound */
        now = ( inl ( pm_tmr ) & ACPI_TIMER_MASK );
        if ( now < prev ) {
                offset += ( ( ACPI_TIMER_MASK + 1 ) /
                            ( ACPI_TIMER_HZ / TICKS_PER_SEC ) );
        }
        prev = now;

        /* Convert to timer ticks */
        return ( offset + ( now / ( ACPI_TIMER_HZ / TICKS_PER_SEC ) ) );
}

/**
 * Delay for a fixed number of microseconds
 *
 * @v usecs             Number of microseconds for which to delay
 */
static void acpi_udelay ( unsigned long usecs ) {
        uint32_t start;
        uint32_t elapsed;
        uint32_t threshold;

        /* Delay until a suitable number of ticks have elapsed.  We do
         * not need to allow for multiple wraparound, since the
         * wraparound period for a 24-bit timer at 3.579545MHz is
         * around 4700000us.
         */
        start = inl ( pm_tmr );
        threshold = ( ( usecs * ACPI_TIMER_HZ ) / 1000000 );
        do {
                elapsed = ( ( inl ( pm_tmr ) - start ) & ACPI_TIMER_MASK );
        } while ( elapsed < threshold );
}

/**
 * Probe ACPI power management timer
 *
 * @ret rc              Return status code
 */
static int acpi_timer_probe ( void ) {
        struct acpi_fadt fadtab;
        userptr_t fadt;
        unsigned int pm_tmr_blk;

        /* Locate FADT */
        fadt = acpi_table ( FADT_SIGNATURE, 0 );
        if ( ! fadt ) {
                DBGC ( &acpi_timer, "ACPI could not find FADT\n" );
                return -ENOENT;
        }

        /* Read FADT */
        copy_from_user ( &fadtab, fadt, 0, sizeof ( fadtab ) );
        pm_tmr_blk = le32_to_cpu ( fadtab.pm_tmr_blk );
        if ( ! pm_tmr_blk ) {
                DBGC ( &acpi_timer, "ACPI has no timer\n" );
                return -ENOENT;
        }

        /* Record power management timer register address */
        pm_tmr = ( pm_tmr_blk + ACPI_PM_TMR );

        return 0;
}

/** ACPI timer */
struct timer acpi_timer __timer ( TIMER_PREFERRED ) = {
        .name = "acpi",
        .probe = acpi_timer_probe,
        .currticks = acpi_currticks,
        .udelay = acpi_udelay,
};