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path: root/hw/timer/sse-timer.c
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/*
 * Arm SSE Subsystem System Timer
 *
 * Copyright (c) 2020 Linaro Limited
 * Written by Peter Maydell
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 or
 * (at your option) any later version.
 */

/*
 * This is a model of the "System timer" which is documented in
 * the Arm SSE-123 Example Subsystem Technical Reference Manual:
 * https://developer.arm.com/documentation/101370/latest/
 *
 * The timer is based around a simple 64-bit incrementing counter
 * (readable from CNTPCT_HI/LO). The timer fires when
 *  Counter - CompareValue >= 0.
 * The CompareValue is guest-writable, via CNTP_CVAL_HI/LO.
 * CNTP_TVAL is an alternative view of the CompareValue defined by
 *  TimerValue = CompareValue[31:0] - Counter[31:0]
 * which can be both read and written.
 * This part is similar to the generic timer in an Arm A-class CPU.
 *
 * The timer also has a separate auto-increment timer. When this
 * timer is enabled, then the AutoIncrValue is set to:
 *  AutoIncrValue = Reload + Counter
 * and this timer fires when
 *  Counter - AutoIncrValue >= 0
 * at which point, an interrupt is generated and the new AutoIncrValue
 * is calculated.
 * When the auto-increment timer is enabled, interrupt generation
 * via the compare/timervalue registers is disabled.
 */
#include "qemu/osdep.h"
#include "qemu/log.h"
#include "qemu/timer.h"
#include "qapi/error.h"
#include "trace.h"
#include "hw/timer/sse-timer.h"
#include "hw/sysbus.h"
#include "hw/irq.h"
#include "hw/registerfields.h"
#include "hw/clock.h"
#include "hw/qdev-clock.h"
#include "migration/vmstate.h"

REG32(CNTPCT_LO, 0x0)
REG32(CNTPCT_HI, 0x4)
REG32(CNTFRQ, 0x10)
REG32(CNTP_CVAL_LO, 0x20)
REG32(CNTP_CVAL_HI, 0x24)
REG32(CNTP_TVAL, 0x28)
REG32(CNTP_CTL, 0x2c)
    FIELD(CNTP_CTL, ENABLE, 0, 1)
    FIELD(CNTP_CTL, IMASK, 1, 1)
    FIELD(CNTP_CTL, ISTATUS, 2, 1)
REG32(CNTP_AIVAL_LO, 0x40)
REG32(CNTP_AIVAL_HI, 0x44)
REG32(CNTP_AIVAL_RELOAD, 0x48)
REG32(CNTP_AIVAL_CTL, 0x4c)
    FIELD(CNTP_AIVAL_CTL, EN, 0, 1)
    FIELD(CNTP_AIVAL_CTL, CLR, 1, 1)
REG32(CNTP_CFG, 0x50)
    FIELD(CNTP_CFG, AIVAL, 0, 4)
#define R_CNTP_CFG_AIVAL_IMPLEMENTED 1
REG32(PID4, 0xFD0)
REG32(PID5, 0xFD4)
REG32(PID6, 0xFD8)
REG32(PID7, 0xFDC)
REG32(PID0, 0xFE0)
REG32(PID1, 0xFE4)
REG32(PID2, 0xFE8)
REG32(PID3, 0xFEC)
REG32(CID0, 0xFF0)
REG32(CID1, 0xFF4)
REG32(CID2, 0xFF8)
REG32(CID3, 0xFFC)

/* PID/CID values */
static const int timer_id[] = {
    0x04, 0x00, 0x00, 0x00, /* PID4..PID7 */
    0xb7, 0xb0, 0x0b, 0x00, /* PID0..PID3 */
    0x0d, 0xf0, 0x05, 0xb1, /* CID0..CID3 */
};

static bool sse_is_autoinc(SSETimer *s)
{
    return (s->cntp_aival_ctl & R_CNTP_AIVAL_CTL_EN_MASK) != 0;
}

static bool sse_enabled(SSETimer *s)
{
    return (s->cntp_ctl & R_CNTP_CTL_ENABLE_MASK) != 0;
}

static uint64_t sse_cntpct_for_timestamp(SSETimer *s, uint64_t now)
{
    /* Return the CNTPCT value for a particular timestamp (clock ns value) */
    return s->ticks_then + clock_ns_to_ticks(s->clk, now - s->ns_then);
}

static uint64_t sse_cntpct(SSETimer *s)
{
    /* Return the CNTPCT value for the current time */
    return sse_cntpct_for_timestamp(s, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL));
}

static bool sse_timer_status(SSETimer *s)
{
    /*
     * Return true if timer condition is met. This is used for both
     * the CNTP_CTL.ISTATUS bit and for whether (unless masked) we
     * assert our IRQ.
     * The documentation is unclear about the behaviour of ISTATUS when
     * in autoincrement mode; we assume that it follows CNTP_AIVAL_CTL.CLR
     * (ie whether the autoincrement timer is asserting the interrupt).
     */
    if (!sse_enabled(s)) {
        return false;
    }

    if (sse_is_autoinc(s)) {
        return s->cntp_aival_ctl & R_CNTP_AIVAL_CTL_CLR_MASK;
    } else {
        return sse_cntpct(s) >= s->cntp_cval;
    }
}

static void sse_update_irq(SSETimer *s)
{
    bool irqstate = (!(s->cntp_ctl & R_CNTP_CTL_IMASK_MASK) &&
                     sse_timer_status(s));

    qemu_set_irq(s->irq, irqstate);
}

static void sse_set_timer(SSETimer *s, uint64_t nexttick)
{
    /* Set the timer to expire at nexttick */
    uint64_t expiry = clock_ticks_to_ns(s->clk, nexttick);

    if (expiry <= INT64_MAX) {
        timer_mod_ns(&s->timer, expiry);
    } else {
        /*
         * nexttick is so far in the future that it would overflow the
         * signed 64-bit range of a QEMUTimer. Since timer_mod_ns()
         * expiry times are absolute, not relative, we are never going
         * to be able to set the timer to this value, so we must just
         * assume that guest execution can never run so long that it
         * reaches the theoretical point when the timer fires.
         */
        timer_del(&s->timer);
    }
}

static void sse_recalc_timer(SSETimer *s)
{
    /* Recalculate the normal timer */
    uint64_t count, nexttick;

    if (sse_is_autoinc(s)) {
        return;
    }

    if (!sse_enabled(s)) {
        timer_del(&s->timer);
        return;
    }

    count = sse_cntpct(s);

    if (count >= s->cntp_cval) {
        /*
         * Timer condition already met. In theory we have a transition when
         * the count rolls back over to 0, but that is so far in the future
         * that it is not representable as a timer_mod() expiry, so in
         * fact sse_set_timer() will always just delete the timer.
         */
        nexttick = UINT64_MAX;
    } else {
        /* Next transition is when count hits cval */
        nexttick = s->cntp_cval;
    }
    sse_set_timer(s, nexttick);
}

static void sse_autoinc(SSETimer *s)
{
    /* Auto-increment the AIVAL, and set the timer accordingly */
    s->cntp_aival = sse_cntpct(s) + s->cntp_aival_reload;
    sse_set_timer(s, s->cntp_aival);
}

static void sse_timer_cb(void *opaque)
{
    SSETimer *s = SSE_TIMER(opaque);

    if (sse_is_autoinc(s)) {
        uint64_t count = sse_cntpct(s);

        if (count >= s->cntp_aival) {
            /* Timer condition met, set CLR and do another autoinc */
            s->cntp_aival_ctl |= R_CNTP_AIVAL_CTL_CLR_MASK;
            s->cntp_aival = count + s->cntp_aival_reload;
        }
        sse_set_timer(s, s->cntp_aival);
    } else {
        sse_recalc_timer(s);
    }
}

static uint64_t sse_timer_read(void *opaque, hwaddr offset, unsigned size)
{
    SSETimer *s = SSE_TIMER(opaque);
    uint64_t r;

    switch (offset) {
    case A_CNTPCT_LO:
        r = extract64(sse_cntpct(s), 0, 32);
        break;
    case A_CNTPCT_HI:
        r = extract64(sse_cntpct(s), 32, 32);
        break;
    case A_CNTFRQ:
        r = s->cntfrq;
        break;
    case A_CNTP_CVAL_LO:
        r = extract64(s->cntp_cval, 0, 32);
        break;
    case A_CNTP_CVAL_HI:
        r = extract64(s->cntp_cval, 32, 32);
        break;
    case A_CNTP_TVAL:
        r = extract64(s->cntp_cval - sse_cntpct(s), 0, 32);
        break;
    case A_CNTP_CTL:
        r = s->cntp_ctl;
        if (sse_timer_status(s)) {
            r |= R_CNTP_CTL_ISTATUS_MASK;
        }
        break;
    case A_CNTP_AIVAL_LO:
        r = extract64(s->cntp_aival, 0, 32);
        break;
    case A_CNTP_AIVAL_HI:
        r = extract64(s->cntp_aival, 32, 32);
        break;
    case A_CNTP_AIVAL_RELOAD:
        r = s->cntp_aival_reload;
        break;
    case A_CNTP_CFG:
        r = R_CNTP_CFG_AIVAL_IMPLEMENTED << R_CNTP_CFG_AIVAL_SHIFT;
        break;
    case A_PID4 ... A_CID3:
        r = timer_id[(offset - A_PID4) / 4];
        break;
    case A_CNTP_AIVAL_CTL:
        qemu_log_mask(LOG_GUEST_ERROR,
                      "SSE System Timer read: read to WO offset 0x%x\n",
                      (unsigned)offset);
        r = 0;
        break;
    default:
        qemu_log_mask(LOG_GUEST_ERROR,
                      "SSE System Timer read: bad offset 0x%x",
                      (unsigned) offset);
        r = 0;
        break;
    }

    trace_sse_timer_read(offset, r, size);
    return r;
}

static void sse_timer_write(void *opaque, hwaddr offset, uint64_t value,
                            unsigned size)
{
    SSETimer *s = SSE_TIMER(opaque);

    trace_sse_timer_write(offset, value, size);

    switch (offset) {
    case A_CNTFRQ:
        s->cntfrq = value;
        break;
    case A_CNTP_CVAL_LO:
        s->cntp_cval = deposit64(s->cntp_cval, 0, 32, value);
        sse_recalc_timer(s);
        break;
    case A_CNTP_CVAL_HI:
        s->cntp_cval = deposit64(s->cntp_cval, 32, 32, value);
        sse_recalc_timer(s);
        break;
    case A_CNTP_TVAL:
        s->cntp_cval = sse_cntpct(s) + sextract64(value, 0, 32);
        sse_recalc_timer(s);
        break;
    case A_CNTP_CTL:
    {
        uint32_t old_ctl = s->cntp_ctl;
        value &= R_CNTP_CTL_ENABLE_MASK | R_CNTP_CTL_IMASK_MASK;
        s->cntp_ctl = value;
        if ((old_ctl ^ s->cntp_ctl) & R_CNTP_CTL_ENABLE_MASK) {
            if (sse_enabled(s)) {
                if (sse_is_autoinc(s)) {
                    sse_autoinc(s);
                } else {
                    sse_recalc_timer(s);
                }
            }
        }
        sse_update_irq(s);
        break;
    }
    case A_CNTP_AIVAL_RELOAD:
        s->cntp_aival_reload = value;
        break;
    case A_CNTP_AIVAL_CTL:
    {
        uint32_t old_ctl = s->cntp_aival_ctl;

        /* EN bit is writeable; CLR bit is write-0-to-clear, write-1-ignored */
        s->cntp_aival_ctl &= ~R_CNTP_AIVAL_CTL_EN_MASK;
        s->cntp_aival_ctl |= value & R_CNTP_AIVAL_CTL_EN_MASK;
        if (!(value & R_CNTP_AIVAL_CTL_CLR_MASK)) {
            s->cntp_aival_ctl &= ~R_CNTP_AIVAL_CTL_CLR_MASK;
        }
        if ((old_ctl ^ s->cntp_aival_ctl) & R_CNTP_AIVAL_CTL_EN_MASK) {
            /* Auto-increment toggled on/off */
            if (sse_enabled(s)) {
                if (sse_is_autoinc(s)) {
                    sse_autoinc(s);
                } else {
                    sse_recalc_timer(s);
                }
            }
        }
        sse_update_irq(s);
        break;
    }
    case A_CNTPCT_LO:
    case A_CNTPCT_HI:
    case A_CNTP_CFG:
    case A_CNTP_AIVAL_LO:
    case A_CNTP_AIVAL_HI:
    case A_PID4 ... A_CID3:
        qemu_log_mask(LOG_GUEST_ERROR,
                      "SSE System Timer write: write to RO offset 0x%x\n",
                      (unsigned)offset);
        break;
    default:
        qemu_log_mask(LOG_GUEST_ERROR,
                      "SSE System Timer write: bad offset 0x%x\n",
                      (unsigned)offset);
        break;
    }
}

static const MemoryRegionOps sse_timer_ops = {
    .read = sse_timer_read,
    .write = sse_timer_write,
    .endianness = DEVICE_LITTLE_ENDIAN,
    .valid.min_access_size = 4,
    .valid.max_access_size = 4,
};

static void sse_timer_reset(DeviceState *dev)
{
    SSETimer *s = SSE_TIMER(dev);

    trace_sse_timer_reset();

    timer_del(&s->timer);
    s->cntfrq = 0;
    s->cntp_ctl = 0;
    s->cntp_cval = 0;
    s->cntp_aival = 0;
    s->cntp_aival_ctl = 0;
    s->cntp_aival_reload = 0;
    s->ns_then = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
    s->ticks_then = 0;
}

static void sse_clk_callback(void *opaque, ClockEvent event)
{
    SSETimer *s = SSE_TIMER(opaque);
    uint64_t now;

    switch (event) {
    case ClockPreUpdate:
        /*
         * Before the clock period updates, set (ticks_then, ns_then)
         * to the current time and tick count (as calculated with
         * the old clock period).
         */
        now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
        s->ticks_then = sse_cntpct_for_timestamp(s, now);
        s->ns_then = now;
        break;
    case ClockUpdate:
        /* Now the clock period has updated, recalculate the timer expiry */
        if (sse_enabled(s)) {
            if (sse_is_autoinc(s)) {
                sse_set_timer(s, s->cntp_aival);
            } else {
                sse_recalc_timer(s);
            }
        }
        break;
    default:
        break;
    }
}

static void sse_timer_init(Object *obj)
{
    SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
    SSETimer *s = SSE_TIMER(obj);

    s->clk = qdev_init_clock_in(DEVICE(obj), "CLK", sse_clk_callback, s,
                                ClockPreUpdate | ClockUpdate);
    memory_region_init_io(&s->iomem, obj, &sse_timer_ops,
                          s, "sse-timer", 0x1000);
    sysbus_init_mmio(sbd, &s->iomem);
    sysbus_init_irq(sbd, &s->irq);
}

static void sse_timer_realize(DeviceState *dev, Error **errp)
{
    SSETimer *s = SSE_TIMER(dev);

    if (!clock_has_source(s->clk)) {
        error_setg(errp, "SSE system timer: CLK must be connected");
        return;
    }

    timer_init_ns(&s->timer, QEMU_CLOCK_VIRTUAL, sse_timer_cb, s);
}

static const VMStateDescription sse_timer_vmstate = {
    .name = "sse-timer",
    .version_id = 1,
    .minimum_version_id = 1,
    .fields = (VMStateField[]) {
        VMSTATE_CLOCK(clk, SSETimer),
        VMSTATE_TIMER(timer, SSETimer),
        VMSTATE_UINT32(cntfrq, SSETimer),
        VMSTATE_UINT32(cntp_ctl, SSETimer),
        VMSTATE_UINT64(cntp_cval, SSETimer),
        VMSTATE_UINT64(cntp_aival, SSETimer),
        VMSTATE_UINT32(cntp_aival_ctl, SSETimer),
        VMSTATE_UINT32(cntp_aival_reload, SSETimer),
        VMSTATE_END_OF_LIST()
    }
};

static void sse_timer_class_init(ObjectClass *klass, void *data)
{
    DeviceClass *dc = DEVICE_CLASS(klass);

    dc->realize = sse_timer_realize;
    dc->vmsd = &sse_timer_vmstate;
    dc->reset = sse_timer_reset;
}

static const TypeInfo sse_timer_info = {
    .name = TYPE_SSE_TIMER,
    .parent = TYPE_SYS_BUS_DEVICE,
    .instance_size = sizeof(SSETimer),
    .instance_init = sse_timer_init,
    .class_init = sse_timer_class_init,
};

static void sse_timer_register_types(void)
{
    type_register_static(&sse_timer_info);
}

type_init(sse_timer_register_types);