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.
CJ
