cs5535-mfgpt: reuse timers that have never been set up

The MFGPT hardware may be set up only once, therefore
cs5535_mfgpt_free_timer() didn't re-set the timer's "avail" bit. However
if a timer is freed before it has actually been in use then it may be made
available again.

Signed-off-by: Jens Rottmann <[e-mail]>
Acked-by: Andres Salomon <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Jordan Crouse <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/misc/cs5535-mfgpt.c

···
  */
 void cs5535_mfgpt_free_timer(struct cs5535_mfgpt_timer *timer)
 {
+	unsigned long flags;
+	uint16_t val;
+
+	/* timer can be made available again only if never set up */
+	val = cs5535_mfgpt_read(timer, MFGPT_REG_SETUP);
+	if (!(val & MFGPT_SETUP_SETUP)) {
+		spin_lock_irqsave(&timer->chip->lock, flags);
+		__set_bit(timer->nr, timer->chip->avail);
+		spin_unlock_irqrestore(&timer->chip->lock, flags);
+	}
+
 	kfree(timer);
 }
 EXPORT_SYMBOL_GPL(cs5535_mfgpt_free_timer);