On Fri, Jul 20, 2012 at 4:03 PM, Oliver Neukum <oneukum@xxxxxxx> wrote:
> 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?
No
>
>> + 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.
Like this:
val = swab16p((__le16 *)buf);
data->temperature = ((21875 * val) >> 13) - 45000;
val = swab16p((__le16 *)(buf+2));
data->humidity = ((15000 * val) >> 13) - 10000;
>
>> + 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
>
Thanks, Johannes
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