Hi Bernhard, This is a well-known issue on the Raspberry Pi whose i2c stretching timeout is too short to allow proper HTU21 conversion. See this discussion over here which provides a patch to allow hold master mode on the Raspberry Pi: https://github.com/raspberrypi/linux/issues/211
We will soon publish a new version of the HTU21 driver which provides a lot of new features including both hold master and no hold measurement modes support. Best regards, William MARKEZANA Advanced Development MEAS France Impasse Jeanne Benozzi CS 83163 31027 Toulouse Cedex 3 Direct : + 33 (0) 582 082 286 Fax : + 33 (0) 582 082 151 william.markez...@meas-spec.com http://www.meas-spec.com -----Message d'origine----- De : Bernhard Walle [mailto:bernh...@bwalle.de] Envoyé : mardi 9 septembre 2014 10:57 À : Markezana, William; li...@roeck-us.net Cc : jdelv...@suse.de; lm-sens...@lm-sensors.org; linux-kernel@vger.kernel.org; Bernhard Walle Objet : [PATCH] hwmon: (htu21) Use the nohold mode to read out values 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
