[PATCH] hwmon: (htu21) Use the nohold mode to read out values

[Bernhard Walle]

On my Raspberry Pi, the driver doesn't work. Every read fails with -EIO.
Reading the data sheet and experimenting a bit made me finding out that
using the nohold mode works. The Raspberry Pi IÂC chip seems to have
problems with slaves blocking the SCK line.

In any case, freeing the bus while performing the measurement seems to
be the better way, I think.

Signed-off-by: Bernhard Walle <bernhard@xxxxxxxxx>
---
 drivers/hwmon/htu21.c | 52 +++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 46 insertions(+), 6 deletions(-)

diff --git a/drivers/hwmon/htu21.c b/drivers/hwmon/htu21.c
index 839086e..7defae2 100644
--- a/drivers/hwmon/htu21.c
+++ b/drivers/hwmon/htu21.c
@@ -25,10 +25,11 @@
 #include <linux/mutex.h>
 #include <linux/device.h>
 #include <linux/jiffies.h>
+#include <linux/delay.h>
 
 /* HTU21 Commands */
-#define HTU21_T_MEASUREMENT_HM	0xE3
-#define HTU21_RH_MEASUREMENT_HM	0xE5
+#define HTU21_T_MEASUREMENT_HM_NOHOLD	0xF3
+#define HTU21_RH_MEASUREMENT_HM_NOHOLD	0xF5
 
 struct htu21 {
 	struct device *hwmon_dev;
@@ -59,6 +60,47 @@ static inline int htu21_rh_ticks_to_per_cent_mille(int ticks)
 	return ((15625 * ticks) >> 13) - 6000;
 }
 
+/* retry for one second, then give up */
+#define MAX_RETRIES 20
+
+static int htu21_read_word(struct i2c_client *client, u8 command)
+{
+	char data[2];
+	int ret, i;
+
+	/* start the measurement */
+	ret = i2c_master_send(client, &command, sizeof(command));
+	if (ret < 0) {
+		dev_err(&client->dev, "Unable to send command 0x%hhx: %d\n",
+				command, ret);
+		return ret;
+	}
+
+	/*
+	 * Now poll until we get the data. On I2C level the device sends a NAK
+	 * until it is ready
+	 */
+
+	msleep(50);
+
+	for (i = 0; i < MAX_RETRIES; i++) {
+		ret = i2c_master_recv(client, data, sizeof(data));
+		if (ret == sizeof(data))
+			break;
+
+		msleep(50);
+	}
+
+	if (ret < 0) {
+		dev_err(&client->dev, "Unable to receive result from command 0x%hhx: %d\n",
+				command, ret);
+		return ret;
+	}
+
+	return (data[0] << 8) | data[1];
+}
+
+
 static int htu21_update_measurements(struct i2c_client *client)
 {
 	int ret = 0;
@@ -68,13 +110,11 @@ static int htu21_update_measurements(struct i2c_client *client)
 
 	if (time_after(jiffies, htu21->last_update + HZ / 2) ||
 	    !htu21->valid) {
-		ret = i2c_smbus_read_word_swapped(client,
-						  HTU21_T_MEASUREMENT_HM);
+		ret = htu21_read_word(client, HTU21_T_MEASUREMENT_HM_NOHOLD);
 		if (ret < 0)
 			goto out;
 		htu21->temperature = htu21_temp_ticks_to_millicelsius(ret);
-		ret = i2c_smbus_read_word_swapped(client,
-						  HTU21_RH_MEASUREMENT_HM);
+		ret = htu21_read_word(client, HTU21_RH_MEASUREMENT_HM_NOHOLD);
 		if (ret < 0)
 			goto out;
 		htu21->humidity = htu21_rh_ticks_to_per_cent_mille(ret);
-- 
2.1.0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/