On 20/08/15 15:11, Nicola Corna wrote:
> The Si7013/20/21 modules support 2 read modes:
> * Hold mode, where the device stretches the clock until the end of the
> measurement
> * No Hold mode, where the device replies NACK for every I2C call during
> the measurement
> Here the No Hold mode is implemented, selectable with the boolean
> parameter holdmode=N. The No Hold mode is less efficient, since it
> requires multiple calls to the device, but it can be used as a fallback if
> the clock stretching is not supported.
Interesting. Strikes me as something that should really be handled via the i2c
core (and device tree or similar bindings) rather than inside a driver as
a module parameter. Perhaps info provided to the i2c client driver
via a check on whether the device supports clock stretching?
I'd like input from Jean on this.
>
> Signed-off-by: Nicola Corna <nicola@xxxxxxxxxx>
> ---
> I've tested this on a Raspberry Pi 2, where the clock stretching is
> currently bugged.
> drivers/iio/humidity/si7020.c | 55 +++++++++++++++++++++++++++++++++++++------
> 1 file changed, 48 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
> index 62fdbcf..a8bad04 100644
> --- a/drivers/iio/humidity/si7020.c
> +++ b/drivers/iio/humidity/si7020.c
> @@ -2,6 +2,7 @@
> * si7020.c - Silicon Labs Si7013/20/21 Relative Humidity and Temp Sensors
> * Copyright (c) 2013,2014 Uplogix, Inc.
> * David Barksdale <dbarksdale@xxxxxxxxxxx>
> + * Copyright (c) 2015 Nicola Corna <nicola@xxxxxxxxxx>
> *
> * This program is free software; you can redistribute it and/or modify it
> * under the terms and conditions of the GNU General Public License,
> @@ -30,16 +31,33 @@
> #include <linux/module.h>
> #include <linux/slab.h>
> #include <linux/sysfs.h>
> +#include <linux/jiffies.h>
>
> #include <linux/iio/iio.h>
> #include <linux/iio/sysfs.h>
>
> /* Measure Relative Humidity, Hold Master Mode */
> #define SI7020CMD_RH_HOLD 0xE5
> +/* Measure Relative Humidity, No Hold Master Mode */
> +#define SI7020CMD_RH_NO_HOLD 0xF5
> /* Measure Temperature, Hold Master Mode */
> #define SI7020CMD_TEMP_HOLD 0xE3
> +/* Measure Temperature, No Hold Master Mode */
> +#define SI7020CMD_TEMP_NO_HOLD 0xF3
> /* Software Reset */
> #define SI7020CMD_RESET 0xFE
> +/* Relative humidity measurement timeout (us) */
> +#define SI7020_RH_TIMEOUT 22800
> +/* Temperature measurement timeout (us) */
> +#define SI7020_TEMP_TIMEOUT 10800
> +/* Minimum delay between retries (No Hold Mode) in us */
> +#define SI7020_NOHOLD_SLEEP_MIN 2000
> +/* Maximum delay between retries (No Hold Mode) in us */
> +#define SI7020_NOHOLD_SLEEP_MAX 6000
> +
> +static bool holdmode = 1;
> +module_param(holdmode, bool, 0644);
> +MODULE_PARM_DESC(holdmode, "Select whether the measurement has to be done with Hold Mode (clock stretching) or No Hold Mode (repeated calls)");
>
> static int si7020_read_raw(struct iio_dev *indio_dev,
> struct iio_chan_spec const *chan, int *val,
> @@ -47,16 +65,39 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
> {
> struct i2c_client **client = iio_priv(indio_dev);
> int ret;
> + unsigned char buf[2];
> + unsigned long start;
>
> switch (mask) {
> case IIO_CHAN_INFO_RAW:
> - ret = i2c_smbus_read_word_data(*client,
> - chan->type == IIO_TEMP ?
> - SI7020CMD_TEMP_HOLD :
> - SI7020CMD_RH_HOLD);
> - if (ret < 0)
> - return ret;
> - *val = ret >> 2;
> + if (holdmode) {
> + ret = i2c_smbus_read_word_data(*client,
> + chan->type == IIO_TEMP ?
> + SI7020CMD_TEMP_HOLD :
> + SI7020CMD_RH_HOLD);
> + if (ret < 0)
> + return ret;
> + *val = ret >> 2;
> + } else {
> + ret = i2c_smbus_write_byte(*client,
> + chan->type == IIO_TEMP ?
> + SI7020CMD_TEMP_NO_HOLD :
> + SI7020CMD_RH_NO_HOLD);
> + if (ret < 0)
> + return ret;
> + start = jiffies;
> + while ((ret = i2c_master_recv(*client, buf, 2)) < 0) {
> + if (time_after(jiffies, start +
> + usecs_to_jiffies(
> + chan->type == IIO_TEMP ?
> + SI7020_TEMP_TIMEOUT :
> + SI7020_RH_TIMEOUT)))
> + return ret;
> + usleep_range(SI7020_NOHOLD_SLEEP_MIN,
> + SI7020_NOHOLD_SLEEP_MAX);
> + }
> + *val = ((buf[0] << 8) | buf[1]) >> 2;
> + }
> /*
> * Humidity values can sligthly exceed the 0-100%RH
> * range and should be corrected by software
>
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