hwmon: (bt1-pvt) Wait for the completion with timeout

If the PVT sensor is suddenly powered down while a caller is waiting for
the conversion completion, the request won't be finished and the task will
hang up on this procedure until the power is back up again. Let's call the
wait_for_completion_timeout() method instead to prevent that. The cached
timeout is exactly what we need to predict for how long conversion could
normally last.

Fixes: 87976ce2 ("hwmon: Add Baikal-T1 PVT sensor driver")
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200920110924.19741-4-Sergey.Semin@baikalelectronics.ruSigned-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/bt1-pvt.c

@@ -477,6 +477,7 @@ static int pvt_read_data(struct pvt_hwmon *pvt, enum pvt_sensor_type type,
 			 long *val)
 {
 	struct pvt_cache *cache = &pvt->cache[type];
+	unsigned long timeout;
 	u32 data;
 	int ret;
 
@@ -500,7 +501,14 @@ static int pvt_read_data(struct pvt_hwmon *pvt, enum pvt_sensor_type type,
 	pvt_update(pvt->regs + PVT_INTR_MASK, PVT_INTR_DVALID, 0);
 	pvt_update(pvt->regs + PVT_CTRL, PVT_CTRL_EN, PVT_CTRL_EN);
 
-	wait_for_completion(&cache->conversion);
+	/*
+	 * Wait with timeout since in case if the sensor is suddenly powered
+	 * down the request won't be completed and the caller will hang up on
+	 * this procedure until the power is back up again. Multiply the
+	 * timeout by the factor of two to prevent a false timeout.
+	 */
+	timeout = 2 * usecs_to_jiffies(ktime_to_us(pvt->timeout));
+	ret = wait_for_completion_timeout(&cache->conversion, timeout);
 
 	pvt_update(pvt->regs + PVT_CTRL, PVT_CTRL_EN, 0);
 	pvt_update(pvt->regs + PVT_INTR_MASK, PVT_INTR_DVALID,
@@ -510,6 +518,9 @@ static int pvt_read_data(struct pvt_hwmon *pvt, enum pvt_sensor_type type,
 
 	mutex_unlock(&pvt->iface_mtx);
 
+	if (!ret)
+		return -ETIMEDOUT;
+
 	if (type == PVT_TEMP)
 		*val = pvt_calc_poly(&poly_N_to_temp, data);
 	else