Re: [PATCH 3/4] ALSA: timer: Introduce virtual userspace-driven timers

[Ivan Orlov]

On 7/28/24 07:59, Christophe JAILLET wrote:
> Le 26/07/2024 à 09:47, Ivan Orlov a écrit :
> > Implement two ioctl calls in order to support virtual userspace-driven
> > ALSA timers.
> >
> > The first ioctl is SNDRV_TIMER_IOCTL_CREATE, which gets the
> > snd_utimer_info struct as a parameter and returns a file descriptor of
> > a virtual timer. It also updates the `id` field of the snd_utimer_info
> > struct, which provides a unique identifier for the timer (basically,
> > the subdevice number which can be used when creating timer instances).
> >
> > This patch also introduces a tiny id allocator for the userspace-driven
> > timers, which guarantees that we don't have more than 128 of them in the
> > system.
> >
> > Another ioctl is SNDRV_TIMER_IOCTL_TRIGGER, which allows us to trigger
> > the virtual timer (and calls snd_timer_interrupt for the timer under
> > the hood), causing all of the timer instances binded to this timer to
> > execute their callbacks.
> >
> > The maximum amount of ticks available for the timer is 1 for the sake of
> > simplification of the userspace API. 'start', 'stop', 'open' and 'close'
> > callbacks for the userspace-driven timers are empty since we don't
> > really do any hardware initialization here.
> >
> > Suggested-by: Axel Holzinger <aholzinger@xxxxxx>
> > Signed-off-by: Ivan Orlov <ivan.orlov0322@xxxxxxxxx>
> > ---
>
> ...
>
> > +#ifdef CONFIG_SND_UTIMER
> > +/*
> > + * Since userspace-driven timers are passed to userspace, we need to 
> > have an identifier
> > + * which will allow us to use them (basically, the subdevice number 
> > of udriven timer).
> > + *
> > + * We have a pool of SNDRV_UTIMERS_MAX_COUNT ids from 0 to 
> > (SNDRV_UTIMERS_MAX_COUNT - 1).
> > + * When we take one of them, the corresponding entry in 
> > snd_utimer_ids becomes true.
> > + */
> > +static bool snd_utimer_ids[SNDRV_UTIMERS_MAX_COUNT];
> > +
> > +static void snd_utimer_put_id(struct snd_utimer *utimer)
> > +{
> > +    int timer_id = utimer->id;
> > +
> > +    snd_BUG_ON(timer_id < 0 || timer_id >= SNDRV_UTIMERS_MAX_COUNT);
> > +    snd_utimer_ids[timer_id] = false;
> > +}
> > +
> > +static int snd_utimer_take_id(void)
> > +{
> > +    size_t i;
> > +
> > +    for (i = 0; i < SNDRV_UTIMERS_MAX_COUNT; i++) {
> > +        if (!snd_utimer_ids[i]) {
> > +            snd_utimer_ids[i] = true;
> > +            return i;
> > +        }
> > +    }
> > +
> > +    return -EBUSY;
> > +}
>
> Also the bitmap API could be useful here.

Awesome, will use it in V2.

Thank you!


--
Kind regards,
Ivan Orlov