From 04dac46eaf14f079b39e817d41a8817adb50844e Mon Sep 17 00:00:00 2001
From: Lucas De Marchi <lucas.demarchi@intel.com>
Date: Wed, 15 Mar 2017 00:20:47 -0700
Subject: [PATCH] ist8310: be resilient to bad data coming from sensor

It doesn't hurt to test if the sensor is outputing data in the expected
range and it should help with elimination of spikes in case of errors.
---
 src/drivers/ist8310/ist8310.cpp | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/drivers/ist8310/ist8310.cpp b/src/drivers/ist8310/ist8310.cpp
index 2b66db15b0..03b191fdad 100644
--- a/src/drivers/ist8310/ist8310.cpp
+++ b/src/drivers/ist8310/ist8310.cpp
@@ -87,6 +87,20 @@
 #define IST8310_BUS_I2C_ADDR		0xE
 #define IST8310_DEFAULT_BUS_SPEED	400000
 
+/*
+ * FSR:
+ *   x, y: +- 1600 µT
+ *   z:    +- 2500 µT
+ *
+ * Resolution according to datasheet is 0.3µT/LSB
+ */
+#define IST8310_RESOLUTION	0.3
+
+static const int16_t IST8310_MAX_VAL_XY	= (1600 / IST8310_RESOLUTION) + 1;
+static const int16_t IST8310_MIN_VAL_XY	= -IST8310_MAX_VAL_XY;
+static const int16_t IST8310_MAX_VAL_Z  = (2500 / IST8310_RESOLUTION) + 1;
+static const int16_t IST8310_MIN_VAL_Z  = -IST8310_MAX_VAL_Z;
+
 /* Hardware definitions */
 
 #define ADDR_WAI                0		/* WAI means 'Who Am I'*/
@@ -920,7 +934,7 @@ IST8310::collect()
 
 	if (ret != OK) {
 		perf_count(_comms_errors);
-		DEVICE_DEBUG("data/status read error");
+		DEVICE_DEBUG("I2C read error");
 		goto out;
 	}
 
@@ -929,11 +943,27 @@ IST8310::collect()
 	report.y = (((int16_t)report_buffer.y[1]) << 8) | (int16_t)report_buffer.y[0];
 	report.z = (((int16_t)report_buffer.z[1]) << 8) | (int16_t)report_buffer.z[0];
 
+
+	/*
+	 * Check if value makes sense according to the FSR and Resolution of
+	 * this sensor, discarding outliers
+	 */
+	if (report.x > IST8310_MAX_VAL_XY || report.x < IST8310_MIN_VAL_XY ||
+	    report.y > IST8310_MAX_VAL_XY || report.y < IST8310_MIN_VAL_XY ||
+	    report.z > IST8310_MAX_VAL_Z  || report.z < IST8310_MIN_VAL_Z) {
+		perf_count(_range_errors);
+		DEVICE_DEBUG("data/status read error");
+		goto out;
+	}
+
 	/* temperature measurement is not available on IST8310 */
 	new_report.temperature = 0;
 
 	/*
 	 * raw outputs
+	 *
+	 * Sensor doesn't follow right hand rule, swap x and y to make it obey
+	 * it.
 	 */
 	new_report.x_raw = report.y;
 	new_report.y_raw = report.x;