iio: dht11: Improve logging

* Unify log messages
* Add more DEBUG messages

Apparently this driver is working unreliably on some platforms that I can't
test. Therefore I want an easy way for bug reporters to provide useful
information without making the driver too chatty by default.
Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/humidity/dht11.c

@@ -96,6 +96,24 @@ struct dht11 {
 	struct {s64 ts; int value; }	edges[DHT11_EDGES_PER_READ];
 };
 
+#ifdef CONFIG_DYNAMIC_DEBUG
+/*
+ * dht11_edges_print: show the data as actually received by the
+ *                    driver.
+ */
+static void dht11_edges_print(struct dht11 *dht11)
+{
+	int i;
+
+	dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges);
+	for (i = 1; i < dht11->num_edges; ++i) {
+		dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
+			dht11->edges[i].ts - dht11->edges[i - 1].ts,
+			dht11->edges[i - 1].value ? "high" : "low");
+	}
+}
+#endif /* CONFIG_DYNAMIC_DEBUG */
+
 static unsigned char dht11_decode_byte(char *bits)
 {
 	unsigned char ret = 0;
@@ -119,8 +137,12 @@ static int dht11_decode(struct dht11 *dht11, int offset)
 	for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
 		t = dht11->edges[offset + 2 * i + 2].ts -
 			dht11->edges[offset + 2 * i + 1].ts;
-		if (!dht11->edges[offset + 2 * i + 1].value)
-			return -EIO;  /* lost synchronisation */
+		if (!dht11->edges[offset + 2 * i + 1].value) {
+			dev_dbg(dht11->dev,
+				"lost synchronisation at edge %d\n",
+				offset + 2 * i + 1);
+			return -EIO;
+		}
 		bits[i] = t > DHT11_THRESHOLD;
 	}
 
@@ -130,8 +152,10 @@ static int dht11_decode(struct dht11 *dht11, int offset)
 	temp_dec = dht11_decode_byte(&bits[24]);
 	checksum = dht11_decode_byte(&bits[32]);
 
-	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum)
+	if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) {
+		dev_dbg(dht11->dev, "invalid checksum\n");
 		return -EIO;
+	}
 
 	dht11->timestamp = ktime_get_boot_ns();
 	if (hum_int < 20) {  /* DHT22 */
@@ -182,6 +206,7 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
 	mutex_lock(&dht11->lock);
 	if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boot_ns()) {
 		timeres = ktime_get_resolution_ns();
+		dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres);
 		if (timeres > DHT11_MIN_TIMERES) {
 			dev_err(dht11->dev, "timeresolution %dns too low\n",
 				timeres);
@@ -219,10 +244,13 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
 
 		free_irq(dht11->irq, iio_dev);
 
+#ifdef CONFIG_DYNAMIC_DEBUG
+		dht11_edges_print(dht11);
+#endif
+
 		if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) {
-			dev_err(&iio_dev->dev,
-				"Only %d signal edges detected\n",
-					dht11->num_edges);
+			dev_err(dht11->dev, "Only %d signal edges detected\n",
+				dht11->num_edges);
 			ret = -ETIMEDOUT;
 		}
 		if (ret < 0)