thermal: qoriq: Do not report invalid temperature reading

Before returning measured temperature data to upper layer we need to
make sure that the reading was marked as "valid" to avoid reporting
bogus data.
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Tested-by: Lucas Stach <l.stach@pengutronix.de>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Angus Ainslie (Purism) <angus@akkea.ca>
Cc: linux-imx@nxp.com
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20191210164153.10463-11-andrew.smirnov@gmail.com

drivers/thermal/qoriq_thermal.c

@@ -49,6 +49,7 @@
 #define REGS_TRITSR(n)	(0x100 + 16 * (n)) /* Immediate Temperature
 					    * Site Register
 					    */
+#define TRITSR_V	BIT(31)
 #define REGS_TTRnCR(n)	(0xf10 + 4 * (n)) /* Temperature Range n
 					   * Control Register
 					   */
@@ -81,8 +82,24 @@ static int tmu_get_temp(void *p, int *temp)
 	struct qoriq_sensor *qsensor = p;
 	struct qoriq_tmu_data *qdata = qoriq_sensor_to_data(qsensor);
 	u32 val;
+	/*
+	 * REGS_TRITSR(id) has the following layout:
+	 *
+	 * 31  ... 7 6 5 4 3 2 1 0
+	 *  V          TEMP
+	 *
+	 * Where V bit signifies if the measurement is ready and is
+	 * within sensor range. TEMP is an 8 bit value representing
+	 * temperature in C.
+	 */
+	if (regmap_read_poll_timeout(qdata->regmap,
+				     REGS_TRITSR(qsensor->id),
+				     val,
+				     val & TRITSR_V,
+				     USEC_PER_MSEC,
+				     10 * USEC_PER_MSEC))
+		return -ENODATA;
 
-	regmap_read(qdata->regmap, REGS_TRITSR(qsensor->id), &val);
 	*temp = (val & 0xff) * 1000;
 
 	return 0;