Re: [Qemu-devel] [PATCH] timer/aspeed: fix timer enablement when a reload is not set

[Andrew Jeffery <andrew@aj.id.au>]

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On Tue, 2017-06-06 at 10:55 +0200, Cédric Le Goater wrote:
> When a timer is enabled before a reload value is set, the controller
> waits for a reload value to be set before starting decrementing. This
> fix tries to cover that case by changing the timer expiry only when
> a reload value is valid.
> 
> > Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---
>  hw/timer/aspeed_timer.c | 37 +++++++++++++++++++++++++++++--------
>  1 file changed, 29 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/timer/aspeed_timer.c b/hw/timer/aspeed_timer.c
> index 9b70ee09b07f..50acbf530a3a 100644
> --- a/hw/timer/aspeed_timer.c
> +++ b/hw/timer/aspeed_timer.c
> @@ -130,15 +130,26 @@ static uint64_t calculate_next(struct AspeedTimer *t)
>              next = seq[1];
>          } else if (now < seq[2]) {
>              next = seq[2];
> -        } else {
> +        } else if (t->reload) {
>              reload_ns = muldiv64(t->reload, NANOSECONDS_PER_SECOND, rate);
>              t->start = now - ((now - t->start) % reload_ns);
> +        } else {
> +            /* no reload value, return 0 */
> +            break;
>          }
>      }
>  
>      return next;
>  }
>  
> +static void aspeed_timer_mod(AspeedTimer *t)
> +{
> +    uint64_t next = calculate_next(t);
> +    if (next) {
> +        timer_mod(&t->timer, next);
> +    }
> +}
> +
>  static void aspeed_timer_expire(void *opaque)
>  {
>      AspeedTimer *t = opaque;
> @@ -164,7 +175,7 @@ static void aspeed_timer_expire(void *opaque)
>          qemu_set_irq(t->irq, t->level);
>      }
>  
> -    timer_mod(&t->timer, calculate_next(t));
> +    aspeed_timer_mod(t);
>  }
>  
>  static uint64_t aspeed_timer_get_value(AspeedTimer *t, int reg)
> @@ -227,10 +238,23 @@ static void aspeed_timer_set_value(AspeedTimerCtrlState *s, int timer, int reg,
>                                     uint32_t value)
>  {
>      AspeedTimer *t;
> +    uint32_t old_reload;
>  
>      trace_aspeed_timer_set_value(timer, reg, value);
>      t = &s->timers[timer];
>      switch (reg) {
> +    case TIMER_REG_RELOAD:
> +        old_reload = t->reload;
> +        t->reload = value;
> +
> +        /* If the reload value was not previously set, or zero, and
> +         * the current value is valid, try to start the timer if it is
> +         * enabled.
> +         */
> +        if (old_reload || !t->reload) {
> +            break;
> +        }

Maybe I need more caffeine, but I initially struggled to reconcile the
condition with the comment, as the condition checks the inverse in
order to break while the comment discusses the non-breaking case. 

However, after trying for several minutes, I'm not sure there's an easy
way to improve it.

> +
>      case TIMER_REG_STATUS:
>          if (timer_enabled(t)) {
>              uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> @@ -238,17 +262,14 @@ static void aspeed_timer_set_value(AspeedTimerCtrlState *s, int timer, int reg,
>              uint32_t rate = calculate_rate(t);
>  
>              t->start += muldiv64(delta, NANOSECONDS_PER_SECOND, rate);
> -            timer_mod(&t->timer, calculate_next(t));
> +            aspeed_timer_mod(t);
>          }
>          break;
> -    case TIMER_REG_RELOAD:
> -        t->reload = value;
> -        break;
>      case TIMER_REG_MATCH_FIRST:
>      case TIMER_REG_MATCH_SECOND:
>          t->match[reg - 2] = value;
>          if (timer_enabled(t)) {
> -            timer_mod(&t->timer, calculate_next(t));
> +            aspeed_timer_mod(t);
>          }
>          break;
>      default:
> @@ -268,7 +289,7 @@ static void aspeed_timer_ctrl_enable(AspeedTimer *t, bool enable)
>      trace_aspeed_timer_ctrl_enable(t->id, enable);
>      if (enable) {
>          t->start = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> -        timer_mod(&t->timer, calculate_next(t));
> +        aspeed_timer_mod(t);
>      } else {
>          timer_del(&t->timer);
>      }

Reviewed-by: Andrew Jeffery <andrew@aj.id.au>

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