iio: proximity: as3935: recalibrate RCO after resume

commit 6272c0de upstream.

According to the datasheet the RCO must be recalibrated
on every power-on-reset. Also remove mutex locking in the
calibration function since callers other than the probe
function (which doesn't need it) will have a lock.

Fixes: 24ddb0e4 ("iio: Add AS3935 lightning sensor support")
Cc: George McCollister <george.mccollister@gmail.com>
Signed-off-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/iio/proximity/as3935.c

@@ -263,8 +263,6 @@ static irqreturn_t as3935_interrupt_handler(int irq, void *private)
 
 static void calibrate_as3935(struct as3935_state *st)
 {
-	mutex_lock(&st->lock);
-
 	/* mask disturber interrupt bit */
 	as3935_write(st, AS3935_INT, BIT(5));
 
@@ -274,8 +272,6 @@ static void calibrate_as3935(struct as3935_state *st)
 
 	mdelay(2);
 	as3935_write(st, AS3935_TUNE_CAP, (st->tune_cap / TUNE_CAP_DIV));
-
-	mutex_unlock(&st->lock);
 }
 
 #ifdef CONFIG_PM_SLEEP
@@ -312,6 +308,8 @@ static int as3935_resume(struct spi_device *spi)
 	val &= ~AS3935_AFE_PWR_BIT;
 	ret = as3935_write(st, AS3935_AFE_GAIN, val);
 
+	calibrate_as3935(st);
+
 err_resume:
 	mutex_unlock(&st->lock);