Re: [Qemu-devel] [PATCH] audio: fix audio timer rate conversion bug

["Zoltán Kővágó" <dirty.ice.hu@gmail.com>]

On 2019-04-01 20:59, Volker Rümelin wrote:
> Currently the default audio timer frequency is 10000Hz instead of
> a period of 10000us. Also the audiodev timer-period property gets
> converted like a frequency. Only handling of the legacy
> QEMU_AUDIO_TIMER_PERIOD environment variable is correct because
> it's actually a frequency.
> 
> With this patch the property timer-period is really a timer period
> and QEMU_AUDIO_TIMER_PERIOD remains a frequency.

Good catch!  The legacy config used Hz, frames, bytes, milliseconds and
microseconds quite randomly to define lengths, this one slipped through
my unification attempts.

> 
> This fixes commit 71830221fb23388b32e6516c2fb7a698453a6c5a
> -audiodev command line option basic implementation.
> 
> Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Zoltán Kővágó <DirtY.iCE.hu@gmail.com>

> ---
>  audio/audio.c        | 2 +-
>  audio/audio_legacy.c | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/audio/audio.c b/audio/audio.c
> index 5fd9a58a80..2040762fef 100644
> --- a/audio/audio.c
> +++ b/audio/audio.c
> @@ -1471,7 +1471,7 @@ static int audio_init(Audiodev *dev)
>      if (dev->timer_period <= 0) {
>          s->period_ticks = 1;
>      } else {
> -        s->period_ticks = NANOSECONDS_PER_SECOND / dev->timer_period;
> +        s->period_ticks = dev->timer_period * SCALE_US;
>      }
>  
>      e = qemu_add_vm_change_state_handler (audio_vm_change_state_handler, s);
> diff --git a/audio/audio_legacy.c b/audio/audio_legacy.c
> index 6d140119d9..2fd58cb8ef 100644
> --- a/audio/audio_legacy.c
> +++ b/audio/audio_legacy.c
> @@ -26,6 +26,7 @@
>  #include "audio_int.h"
>  #include "qemu-common.h"
>  #include "qemu/cutils.h"
> +#include "qemu/timer.h"
>  #include "qapi/error.h"
>  #include "qapi/qapi-visit-audio.h"
>  #include "qapi/visitor-impl.h"
> @@ -338,8 +339,13 @@ static AudiodevListEntry *legacy_opt(const char *drvname)
>      handle_per_direction(audio_get_pdo_in(e->dev), "QEMU_AUDIO_ADC_");
>      handle_per_direction(audio_get_pdo_out(e->dev), "QEMU_AUDIO_DAC_");
>  
> +    /* Original description: Timer period in HZ (0 - use lowest possible) */
>      get_int("QEMU_AUDIO_TIMER_PERIOD",
>              &e->dev->timer_period, &e->dev->has_timer_period);
> +    if (e->dev->has_timer_period && e->dev->timer_period) {
> +        e->dev->timer_period = NANOSECONDS_PER_SECOND / 1000 /
> +                               e->dev->timer_period;
> +    }

I'd use SCALE_US instead of 1000 here.  If you have
NANOSECONDS_PER_SECOND / SCALE_US / e->dev->timer_period, it's
immediately obvious that if you multiply it with SCALE_US, you get back
the old value of s->period_ticks above.

>  
>      switch (e->dev->driver) {
>      case AUDIODEV_DRIVER_ALSA:
> 

Regards,
Zoltan