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Re: [Qemu-devel] [PATCH arm-devs v2 1/2] hw/timer: Introduce ARM A9 Glob


From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH arm-devs v2 1/2] hw/timer: Introduce ARM A9 Global Timer.
Date: Mon, 15 Jul 2013 14:20:20 +0100

On 15 July 2013 06:19,  <address@hidden> wrote:
> From: Peter Crosthwaite <address@hidden>
>
> The ARM A9 MPCore has a timer that is global to all CPUs in the mpcore.
> The timer is shared but each CPU has a private independent comparator
> and interrupt.
>
> Based on version contributed by Francois LEGAL.
>
> Signed-off-by: Fran├žois LEGAL <address@hidden>
> [PC changes:
>  * New commit message
>  * Re-implemented as single timer model
>  * Fixed backwards counting issue in polled mode
>  * completed VMSD fields
>  * macroified magic numbers (and headerified reg definitions)
>  * split of as device-model-only patch
>  * use bitops for 64 bit register access
>  * Fixed auto increment mode to check condition properly
>  * general cleanup (names etc).
> ]
> Signed-off-by: Peter Crosthwaite <address@hidden>
> ---
> Changed since v1:
> Added /*< private >*/ to struct definition.
> Pulled register definitions out into a header (AF review)
> SOB Francois LEGAL with PC changes indicated.
>
>  hw/timer/Makefile.objs      |   2 +-
>  hw/timer/a9gtimer.c         | 412 
> ++++++++++++++++++++++++++++++++++++++++++++
>  include/hw/timer/a9gtimer.h |  33 ++++
>  3 files changed, 446 insertions(+), 1 deletion(-)
>  create mode 100644 hw/timer/a9gtimer.c
>  create mode 100644 include/hw/timer/a9gtimer.h
>
> diff --git a/hw/timer/Makefile.objs b/hw/timer/Makefile.objs
> index eca5905..42d96df 100644
> --- a/hw/timer/Makefile.objs
> +++ b/hw/timer/Makefile.objs
> @@ -1,5 +1,5 @@
>  common-obj-$(CONFIG_ARM_TIMER) += arm_timer.o
> -common-obj-$(CONFIG_ARM_MPTIMER) += arm_mptimer.o
> +common-obj-$(CONFIG_ARM_MPTIMER) += arm_mptimer.o a9gtimer.o

As I understand it, a new device should have its own
CONFIG_WHATEVER switch set in default-configs/arm-softmmu.mak;
we shouldn't share them. (The eventual idea is that you might
want to disable some boards, in which case a config with
only 11mpcore boards and no a9 boards would want the
arm_mptimer but not the a9gtimer compiled.)

>  common-obj-$(CONFIG_CADENCE) += cadence_ttc.o
>  common-obj-$(CONFIG_DS1338) += ds1338.o
>  common-obj-$(CONFIG_HPET) += hpet.o
> diff --git a/hw/timer/a9gtimer.c b/hw/timer/a9gtimer.c
> new file mode 100644
> index 0000000..72ebeba
> --- /dev/null
> +++ b/hw/timer/a9gtimer.c
> @@ -0,0 +1,412 @@
> +/*
> + * Global peripheral timer block for ARM A9MP
> + *
> + * (C) 2013 Xilinx Inc.
> + *
> + * Written by Fran├žois LEGAL
> + * Written by Peter Crosthwaite <address@hidden>
> + *
> + * 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 (at your option) 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, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include "hw/sysbus.h"
> +#include "qemu/timer.h"
> +#include "qemu/bitops.h"
> +#include "qemu/log.h"
> +
> +#include "hw/timer/a9gtimer.h"
> +
> +#ifndef ARM_GTIMER_ERR_DEBUG
> +#define ARM_GTIMER_ERR_DEBUG 0
> +#endif
> +
> +#define DB_PRINT_L(level, ...) do { \
> +    if (ARM_GTIMER_ERR_DEBUG > (level)) { \
> +        fprintf(stderr,  ": %s: ", __func__); \
> +        fprintf(stderr, ## __VA_ARGS__); \
> +    } \
> +} while (0);
> +
> +#define DB_PRINT(...) DB_PRINT_L(0, ## __VA_ARGS__)
> +
> +#define MAX_CPUS 4
> +
> +typedef struct A9GlobalTimerPerCPU A9GlobalTimerPerCPU;
> +typedef struct A9GlobalTimerState A9GlobalTimerState;
> +
> +struct A9GlobalTimerPerCPU {
> +    A9GlobalTimerState *parent;
> +
> +    uint32_t control; /* only per cpu banked bits valid */
> +    uint64_t compare;
> +    uint32_t status;
> +    uint32_t inc;
> +
> +    MemoryRegion iomem;
> +    qemu_irq irq; /* PPI interrupts */
> +};
> +
> +struct A9GlobalTimerState {
> +    /*< private >*/
> +    SysBusDevice parent_obj;
> +    /*< public >*/
> +
> +    MemoryRegion iomem;
> +    /* static props */
> +    uint32_t num_cpu;
> +
> +    QEMUTimer *timer;
> +
> +    uint64_t counter; /* current timer value */
> +
> +    uint64_t ref_counter;
> +    uint64_t cpu_ref_time; /* the cpu time as of last update of ref_counter 
> */

Is it really correct that we migrate one of these fields
but not the other, and don't clear either on reset?

> +    uint32_t control; /* only non per cpu banked bits valid */
> +
> +    A9GlobalTimerPerCPU per_cpu[MAX_CPUS];
> +};
> +
> +typedef struct A9GTimerUpdate {
> +    uint64_t now;
> +    uint64_t new;
> +} A9GTimerUpdate;
> +
> +static inline int a9_gtimer_get_current_cpu(A9GlobalTimerState *s)
> +{
> +    if (current_cpu->cpu_index >= s->num_cpu) {
> +        hw_error("arm_mptimer: num-cpu %d but this cpu is %d!\n",
> +                 s->num_cpu, current_cpu->cpu_index);
> +    }
> +    return current_cpu->cpu_index;
> +}
> +
> +static inline uint64_t a9_gtimer_get_conv(A9GlobalTimerState *s)
> +{
> +    uint64_t prescale = extract32(s->control, R_CONTROL_PRESCALER_SHIFT,
> +                                  R_CONTROL_PRESCALER_LEN);
> +
> +    return (prescale + 1) * 100;

Why do we use * 100 here, but only * 10 in the arm_mptimer
scaling function?

> +}
> +
> +static A9GTimerUpdate a9_gtimer_get_update(A9GlobalTimerState *s)
> +{
> +    A9GTimerUpdate ret;
> +
> +    ret.now = qemu_get_clock_ns(vm_clock);
> +    ret.new = s->ref_counter +
> +              (ret.now - s->cpu_ref_time) / a9_gtimer_get_conv(s);
> +    return ret;
> +}
> +
> +static void a9_gtimer_update(A9GlobalTimerState *s, bool sync)
> +{
> +
> +    A9GTimerUpdate update = a9_gtimer_get_update(s);
> +    int i;
> +    int64_t next_cdiff = 0;
> +
> +    for (i = 0; i < s->num_cpu; ++i) {
> +        A9GlobalTimerPerCPU *gtb = &s->per_cpu[i];
> +        int64_t cdiff = 0;
> +
> +        if ((s->control & R_CONTROL_TIMER_ENABLE) &&
> +                (gtb->control & R_CONTROL_COMP_ENABLE)) {
> +            /* R2p0+, where the compare function is > */

The TRM says it's "greater than or equal to". I think
your code is correct, but this comment is wrong.

> +            while (gtb->compare < update.new) {
> +                DB_PRINT("Compare event happened for CPU %d\n", i);
> +                gtb->status = 1;
> +                if (gtb->control & R_CONTROL_AUTO_INCREMENT) {
> +                    DB_PRINT("Auto incrementing timer compare by %" PRId32 
> "\n",
> +                             gtb->inc);
> +                    gtb->compare += gtb->inc;
> +                } else {
> +                    break;
> +                }
> +            }
> +            cdiff = (int64_t)gtb->compare - (int64_t)update.new + 1;

It looks odd that we're doing our "time to next comparison" in
signed arithmetic, but our "have we fired yet?" check above is
doing an unsigned comparison.

> +            if (cdiff > 0 && (cdiff < next_cdiff || !next_cdiff)) {
> +                next_cdiff = cdiff;
> +            }
> +        }
> +
> +        qemu_set_irq(gtb->irq,
> +                     gtb->status && (gtb->control & R_CONTROL_IRQ_ENABLE));
> +    }
> +
> +    qemu_del_timer(s->timer);
> +    if (next_cdiff) {
> +        DB_PRINT("scheduling qemu_timer to fire again in %"
> +                 PRIx64 " cycles\n", next_cdiff);
> +        qemu_mod_timer(s->timer,
> +                       update.now + next_cdiff * a9_gtimer_get_conv(s));
> +    }
> +
> +    if (s->control & R_CONTROL_TIMER_ENABLE) {
> +        s->counter = update.new;
> +    }
> +
> +    if (sync) {
> +        s->cpu_ref_time = update.now;
> +        s->ref_counter = s->counter;
> +    }
> +}



> +
> +static void a9_gtimer_write(void *opaque, hwaddr addr, uint64_t value,
> +                            unsigned size)
> +{
> +    A9GlobalTimerPerCPU *gtb = (A9GlobalTimerPerCPU *)opaque;
> +    A9GlobalTimerState *s = gtb->parent;
> +    int shift = 0;
> +
> +    DB_PRINT("addr:%#x data:%#08" PRIx64 "\n", (unsigned)addr, value);
> +
> +    switch (addr) {
> +    case R_COUNTER_HI:
> +        shift = 32;
> +        /* fallthrough */
> +    case R_COUNTER_LO:
> +        /*
> +         * Keep it simple - ARM docco explicitly says to disable timer before
> +         * modding it, so dont bother trying to do all the difficult on the 
> fly
> +         * timer modifications - (if they even work in real hardware??).
> +         */

I'm pretty sure the remarks in the TRM are intended as a note to
software authors about how to reliably modify the timer, given
it's a 64 bit field that you can only write 32 bits at a time.
I haven't tested but you'd probably have to go out of your way to
make the h/w not just update the appropriate 32 bits...
I'm happy with this log-and-do-nothing implementation though.

> +        if (s->control & R_CONTROL_TIMER_ENABLE) {
> +            qemu_log_mask(LOG_GUEST_ERROR, "Cannot mod running ARM 
> gtimer\n");
> +            return;
> +        }
> +        s->counter = deposit64(s->counter, shift, 32, value);
> +        return;

> +static void a9_gtimer_reset(DeviceState *dev)
> +{
> +    A9GlobalTimerState *s = ARM_GTIMER(dev);
> +    int i;
> +
> +    s->counter = 0;
> +    s->control = 0;
> +
> +    for (i = 0; i < s->num_cpu; i++) {
> +        A9GlobalTimerPerCPU *gtb = &s->per_cpu[i];
> +
> +        gtb->control = 0;
> +        gtb->status = 0;
> +        gtb->compare = 0;

Missing gtb->inc reset.

> +    }
> +    a9_gtimer_update(s, false);
> +}
> +
> +static void a9_gtimer_realize(DeviceState *dev, Error **errp)
> +{
> +    A9GlobalTimerState *s = ARM_GTIMER(dev);
> +    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> +    int i;
> +
> +    if (s->num_cpu < 1 || s->num_cpu > MAX_CPUS) {
> +        error_setg(errp, "%s: num-cpu must be between 1 and %d\n",
> +                   __func__, MAX_CPUS);
> +    }
> +
> +    memory_region_init_io(&s->iomem, OBJECT(dev), &a9_gtimer_this_ops, s,
> +                          "MMIO shared", 0x20);

This makes the memory region pretty much anonymous in the debugger:

(gdb) print s->iomem
$1 = {ops = 0x555555dca4a0, iommu_ops = 0x0, opaque = 0x5555563e5ab0,
owner = 0x0, parent = 0x0, size = {lo = 32,
    hi = 0}, addr = 0, destructor = 0x5555559420d7
<memory_region_destructor_none>,
  ram_addr = 18446744073709551615, subpage = false, terminates = true,
romd_mode = true, ram = false,
  readonly = false, enabled = true, rom_device = false,
warning_printed = false, flush_coalesced_mmio = false,
  alias = 0x0, alias_offset = 0, priority = 0, may_overlap = false,
subregions = {tqh_first = 0x0,
    tqh_last = 0x5555563e7e50}, subregions_link = {tqe_next = 0x0,
tqe_prev = 0x0}, coalesced = {tqh_first = 0x0,
    tqh_last = 0x5555563e7e70}, name = 0x555556348620 "MMIO shared",
dirty_log_mask = 0 '\000', ioeventfd_nb = 0,
  ioeventfds = 0x0, iommu_notify = {notifiers = {lh_first = 0x0}}}

which isn't very nice given that debugging is the main reason
for naming MMIO regions. Can we have something slightly less
ambiguous, please?

> diff --git a/include/hw/timer/a9gtimer.h b/include/hw/timer/a9gtimer.h
> new file mode 100644
> index 0000000..f4c1499
> --- /dev/null
> +++ b/include/hw/timer/a9gtimer.h
> @@ -0,0 +1,33 @@
> +#ifndef A9GTIMER_H
> +#define A9GTIMER_H
> +
> +#include "qom/object.h"
> +
> +#define TYPE_ARM_GTIMER "arm.cortex-a9-global-timer"

This doesn't match the name you pass to qdev_create() in patch 2,
and so we assert on startup.

> +#define ARM_GTIMER(obj) OBJECT_CHECK(A9GlobalTimerState, (obj), 
> TYPE_ARM_GTIMER)
> +
> +#define R_COUNTER_LO                0x00
> +#define R_COUNTER_HI                0x04
> +
> +#define R_CONTROL                   0x08
> +#define R_CONTROL_TIMER_ENABLE      (1 << 0)
> +#define R_CONTROL_COMP_ENABLE       (1 << 1)
> +#define R_CONTROL_IRQ_ENABLE        (1 << 2)
> +#define R_CONTROL_AUTO_INCREMENT    (1 << 2)
> +#define R_CONTROL_PRESCALER_SHIFT   8
> +#define R_CONTROL_PRESCALER_LEN     8
> +#define R_CONTROL_PRESCALER_MASK    (((1 << R_CONTROL_PRESCALER_LEN) - 1) << 
> \
> +                                     R_CONTROL_PRESCALER_SHIFT)
> +
> +#define R_CONTROL_BANKED            (R_CONTROL_COMP_ENABLE | \
> +                                     R_CONTROL_IRQ_ENABLE | \
> +                                     R_CONTROL_AUTO_INCREMENT)
> +#define R_CONTROL_NEEDS_SYNC        (R_CONTROL_TIMER_ENABLE | \
> +                                     R_CONTROL_PRESCALER_MASK)
> +
> +#define R_INTERRUPT_STATUS          0x0C
> +#define R_COMPARATOR_LO             0x10
> +#define R_COMPARATOR_HI             0x14
> +#define R_AUTO_INCREMENT            0x18

Shouldn't most of these defines be in the .c file, given that
they're only needed by the implementation, not by users of the
device ?

thanks
-- PMM



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