ALSA: timer: Replace tasklet with work

The tasklet is an old API that should be deprecated, usually can be
converted to another decent API. In ALSA core timer API, the
callbacks can be offlined to a tasklet when a flag is set in the timer
backend. It can be achieved gracefully with a work queued in the
high-prio system workqueue.

This patch replaces the usage of tasklet in ALSA timer API with a
simple work. Currently the tasklet feature is used only in the system
timer and hrtimer backends, so both are patched to use the new flag
name SNDRV_TIMER_HW_WORK, too.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

include/sound/timer.h

···
 #define SNDRV_TIMER_HW_STOP	0x00000002	/* call stop before start */
 #define SNDRV_TIMER_HW_SLAVE	0x00000004	/* only slave timer (variable resolution) */
 #define SNDRV_TIMER_HW_FIRST	0x00000008	/* first tick can be incomplete */
-#define SNDRV_TIMER_HW_TASKLET	0x00000010	/* timer is called from tasklet */
+#define SNDRV_TIMER_HW_WORK	0x00000010	/* timer is called from work */
 
 #define SNDRV_TIMER_IFLG_SLAVE	  0x00000001
 #define SNDRV_TIMER_IFLG_RUNNING  0x00000002
 #define SNDRV_TIMER_IFLG_START	  0x00000004
 #define SNDRV_TIMER_IFLG_AUTO	  0x00000008	/* auto restart */
-#define SNDRV_TIMER_IFLG_FAST	  0x00000010	/* fast callback (do not use tasklet) */
+#define SNDRV_TIMER_IFLG_FAST	  0x00000010	/* fast callback (do not use work) */
 #define SNDRV_TIMER_IFLG_CALLBACK 0x00000020	/* timer callback is active */
 #define SNDRV_TIMER_IFLG_EXCLUSIVE 0x00000040	/* exclusive owner - no more instances */
 #define SNDRV_TIMER_IFLG_EARLY_EVENT 0x00000080	/* write early event to the poll queue */
···
 	struct list_head active_list_head;
 	struct list_head ack_list_head;
 	struct list_head sack_list_head; /* slow ack list head */
-	struct tasklet_struct task_queue;
+	struct work_struct task_work;
 	int max_instances;	/* upper limit of timer instances */
 	int num_instances;	/* current number of timer instances */
 };
···
 	unsigned long ticks;		/* auto-load ticks when expired */
 	unsigned long cticks;		/* current ticks */
 	unsigned long pticks;		/* accumulated ticks for callback */
-	unsigned long resolution;	/* current resolution for tasklet */
+	unsigned long resolution;	/* current resolution for work */
 	unsigned long lost;		/* lost ticks */
 	int slave_class;
 	unsigned int slave_id;

sound/core/hrtimer.c

···
 }
 
 static const struct snd_timer_hardware hrtimer_hw __initconst = {
-	.flags =	SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_TASKLET,
+	.flags =	SNDRV_TIMER_HW_AUTO | SNDRV_TIMER_HW_WORK,
 	.open =		snd_hrtimer_open,
 	.close =	snd_hrtimer_close,
 	.start =	snd_hrtimer_start,

sound/core/timer.c

···
 }
 
 /*
- * timer tasklet
+ * timer work
  *
  */
-static void snd_timer_tasklet(struct tasklet_struct *t)
+static void snd_timer_work(struct work_struct *work)
 {
-	struct snd_timer *timer = from_tasklet(timer, t, task_queue);
+	struct snd_timer *timer = container_of(work, struct snd_timer, task_work);
 	unsigned long flags;
 
 	if (timer->card && timer->card->shutdown) {
···
 	unsigned long resolution;
 	struct list_head *ack_list_head;
 	unsigned long flags;
-	int use_tasklet = 0;
+	bool use_work = false;
 
 	if (timer == NULL)
 		return;
···
 			--timer->running;
 			list_del_init(&ti->active_list);
 		}
-		if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) ||
+		if ((timer->hw.flags & SNDRV_TIMER_HW_WORK) ||
 		    (ti->flags & SNDRV_TIMER_IFLG_FAST))
 			ack_list_head = &timer->ack_list_head;
 		else
···
 	snd_timer_process_callbacks(timer, &timer->ack_list_head);
 
 	/* do we have any slow callbacks? */
-	use_tasklet = !list_empty(&timer->sack_list_head);
+	use_work = !list_empty(&timer->sack_list_head);
 	spin_unlock_irqrestore(&timer->lock, flags);
 
-	if (use_tasklet)
-		tasklet_schedule(&timer->task_queue);
+	if (use_work)
+		queue_work(system_highpri_wq, &timer->task_work);
 }
 EXPORT_SYMBOL(snd_timer_interrupt);
 
···
 	INIT_LIST_HEAD(&timer->ack_list_head);
 	INIT_LIST_HEAD(&timer->sack_list_head);
 	spin_lock_init(&timer->lock);
-	tasklet_setup(&timer->task_queue, snd_timer_tasklet);
+	INIT_WORK(&timer->task_work, snd_timer_work);
 	timer->max_instances = 1000; /* default limit per timer */
 	if (card != NULL) {
 		timer->module = card->module;
···
 
 static const struct snd_timer_hardware snd_timer_system =
 {
-	.flags =	SNDRV_TIMER_HW_FIRST | SNDRV_TIMER_HW_TASKLET,
+	.flags =	SNDRV_TIMER_HW_FIRST | SNDRV_TIMER_HW_WORK,
 	.resolution =	1000000000L / HZ,
 	.ticks =	10000000L,
 	.close =	snd_timer_s_close,