thermal/drivers/tsens: Add timeout to get_temp_tsens_valid

The function can loop and lock the system if for whatever reason the bit
for the target sensor is NEVER valid. This is the case if a sensor is
disabled by the factory and the valid bit is never reported as actually
valid. Add a timeout check and exit if a timeout occurs. As this is
a very rare condition, handle the timeout only if the first read fails.
While at it also rework the function to improve readability and convert
to poll_timeout generic macro.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211007172859.583-1-ansuelsmth@gmail.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/thermal/qcom/tsens.c

@@ -603,22 +603,21 @@ int get_temp_tsens_valid(const struct tsens_sensor *s, int *temp)
 	int ret;
 
 	/* VER_0 doesn't have VALID bit */
-	if (tsens_version(priv) >= VER_0_1) {
+	if (tsens_version(priv) == VER_0)
-		ret = regmap_field_read(priv->rf[valid_idx], &valid);
+		goto get_temp;
-		if (ret)
-			return ret;
-		while (!valid) {
-			/* Valid bit is 0 for 6 AHB clock cycles.
-			 * At 19.2MHz, 1 AHB clock is ~60ns.
-			 * We should enter this loop very, very rarely.
-			 */
-			ndelay(400);
-			ret = regmap_field_read(priv->rf[valid_idx], &valid);
-			if (ret)
-				return ret;
-		}
-	}
 
+	/* Valid bit is 0 for 6 AHB clock cycles.
+	 * At 19.2MHz, 1 AHB clock is ~60ns.
+	 * We should enter this loop very, very rarely.
+	 * Wait 1 us since it's the min of poll_timeout macro.
+	 * Old value was 400 ns.
+	 */
+	ret = regmap_field_read_poll_timeout(priv->rf[valid_idx], valid,
+					     valid, 1, 20 * USEC_PER_MSEC);
+	if (ret)
+		return ret;
+
+get_temp:
 	/* Valid bit is set, OK to read the temperature */
 	*temp = tsens_hw_to_mC(s, temp_idx);