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

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Message-ID: <3ab0aa72-4f89-4911-8546-ce17f362c981@gmail.com>
Date: Sun, 28 Jul 2024 09:51:24 +0100
From: Ivan Orlov <ivan.orlov0322@...il.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>, perex@...ex.cz,
 tiwai@...e.com, corbet@....net, broonie@...nel.org, shuah@...nel.org
Cc: linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org, aholzinger@....de
Subject: Re: [PATCH 3/4] ALSA: timer: Introduce virtual userspace-driven
 timers

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@....de>
>> Signed-off-by: Ivan Orlov <ivan.orlov0322@...il.com>
>> ---
> 
> ...
> 
>> +#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