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

[Cédric Le Goater]

On 06/09/2017 04:26 AM, Andrew Jeffery wrote:
> 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 <address@hidden>
>> ---
>>  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. 

I agree. The reload "value" is used in a hidden way to the activate the 
timer.

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

I tried a few things. May be, we could move the following code in 
its own routine and call it twice ? 
 
>> +
>>      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 <address@hidden>

Thanks,

C.