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 I²C 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 <bernh...@bwalle.de>
---
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
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