On Friday 20 July 2012 14:57:22 Johannes Winkelmann wrote:
> +/* sysfs attributes */
> +static struct shtc1_data *shtc1_update_client(struct device *dev)
> +{
> + struct i2c_client *client = to_i2c_client(dev);
> + struct shtc1_data *data = i2c_get_clientdata(client);
> +
> + char buf[SHTC1_RESPONSE_LENGTH];
Is this used for DMA?
> + int val;
> + int ret;
> +
> + mutex_lock(&data->update_lock);
> +
> + /*
> + * initialize 'ret' in case we had a valid result before, but
> + * read too quickly in which case we return the last values
> + */
> + ret = !data->valid;
> +
> + if (time_after(jiffies, data->last_updated + HZ / 10)
> + || !data->valid) {
> + ret = shtc1_update_values(client, data, buf, sizeof(buf));
> +
> + if (ret)
> + goto out;
> +
> + /*
> + * From datasheet:
> + * T = -45 + 175 * ST / 2^16
> + * RH = -10 + 120 * SRH / 2^16
> + *
> + * Adapted for integer fixed point (3 digit) arithmetic
> + */
> + val = (buf[0] << 8) | buf[1];
> + data->temperature = ((21875 * val) >> 13) - 45000;
> + val = (buf[3] << 8) | buf[4];
We have dedicated macros for conversion of endianness.
> + data->humidity = ((15000 * val) >> 13) - 10000;
> +
> + data->last_updated = jiffies;
> + data->valid = 1;
> + }
> +
> +out:
> + mutex_unlock(&data->update_lock);
> +
> + return ret == 0 ? data : NULL;
> +}
Regards
Oliver
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