linux-kernel - Re: [PATCH] iio: humidity: hdc100x: use i2c_master

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Date:	Wed, 3 Aug 2016 21:58:15 -0700
From:	Matt Ranostay <mranostay@...il.com>
To:	Alison Schofield <amsfield22@...il.com>
Cc:	Jonathan Cameron <jic23@...nel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald-Stadler <pmeerw@...erw.net>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: humidity: hdc100x: use i2c_master_recv to read
 sensor data

On Wed, Aug 3, 2016 at 8:33 PM, Alison Schofield <amsfield22@...il.com> wrote:
> Replace the i2c_smbus_read_byte commmands used to retrieve the sensor
> data with an i2c_master_recv command.
>
> The smbus read byte method fails because the device does not expect a
> stop condition after sending the first byte. When we issue the second
> read, we are getting the first byte again. Net effect is that of the 14
> bits used for the measurement, the 8 most significant bits are correct,
> the lower 6 are not.
>
> None of the smbus read protocols follow the pattern this device requires
> (S Addr Rd [A] Data [A] Data NA P), hence the switch to an i2c receive
> transaction.
>
> Signed-off-by: Alison Schofield <amsfield22@...il.com>
> Cc: Daniel Baluta <daniel.baluta@...il.com>
> ---
>  drivers/iio/humidity/hdc100x.c | 27 +++++++--------------------
>  1 file changed, 7 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/iio/humidity/hdc100x.c b/drivers/iio/humidity/hdc100x.c
> index a03832a..643a42d 100644
> --- a/drivers/iio/humidity/hdc100x.c
> +++ b/drivers/iio/humidity/hdc100x.c
> @@ -142,7 +142,7 @@ static int hdc100x_get_measurement(struct hdc100x_data *data,
>         struct i2c_client *client = data->client;
>         int delay = data->adc_int_us[chan->address];
>         int ret;
> -       int val;
> +       u8 buf[2];
>
>         /* start measurement */
>         ret = i2c_smbus_write_byte(client, chan->address);
> @@ -154,26 +154,13 @@ static int hdc100x_get_measurement(struct hdc100x_data *data,
>         /* wait for integration time to pass */
>         usleep_range(delay, delay + 1000);
>
> -       /*
> -        * i2c_smbus_read_word_data cannot() be used here due to the command
> -        * value not being understood and causes NAKs preventing any reading
> -        * from being accessed.
> -        */
> -       ret = i2c_smbus_read_byte(client);
> +       /* read the 2 byte measurement */
> +       ret = i2c_master_recv(data->client, buf, 2);
>         if (ret < 0) {
> -               dev_err(&client->dev, "cannot read high byte measurement");
> +               dev_err(&client->dev, "cannot read sensor data\n");
>                 return ret;
>         }
> -       val = ret << 8;
> -
> -       ret = i2c_smbus_read_byte(client);
> -       if (ret < 0) {
> -               dev_err(&client->dev, "cannot read low byte measurement");
> -               return ret;
> -       }
> -       val |= ret;
> -
> -       return val;
> +       return (int)(buf[0] << 8 | buf[1]);

Pretty sure you don't need to cast to int type here.

>  }
>
>  static int hdc100x_get_heater_status(struct hdc100x_data *data)
> @@ -272,8 +259,8 @@ static int hdc100x_probe(struct i2c_client *client,
>         struct iio_dev *indio_dev;
>         struct hdc100x_data *data;
>
> -       if (!i2c_check_functionality(client->adapter,
> -                               I2C_FUNC_SMBUS_WORD_DATA | I2C_FUNC_SMBUS_BYTE))
> +       if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WORD_DATA |
> +                                    I2C_FUNC_SMBUS_BYTE | I2C_FUNC_I2C))

Not sure we want to kill smbus support for this device...  iwe should
have two read methods for i2c and smbus (see the PulsedLight LIDAR
driver) in this case.

Ideally I wouldn't have written it with only smbus in mind, but can
kill backwards compatibility unless we have a good reason.

Thanks,

Matt

>                 return -EOPNOTSUPP;
>
>         indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> --
> 2.1.4
>