linux-kernel - Re: [PATCH v1 2/2] iio: temperature: add driver support for ti tmp117

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Message-ID: <760dccc2-b098-71ce-037b-b667dbc05f57@metafoo.de>
Date:   Sun, 21 Mar 2021 06:07:31 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Puranjay Mohan <puranjay12@...il.com>,
        alexandru.ardelean@...log.com, jic23@...nel.org,
        devicetree@...r.kernel.org, knaack.h@....de,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] iio: temperature: add driver support for ti tmp117

On 3/20/21 7:45 AM, Puranjay Mohan wrote:
> TMP117 is a Digital temperature sensor with integrated NV memory.
>
> Add support for tmp117 driver in iio subsystem.
>
> Datasheet:-https://www.ti.com/lit/gpn/tmp117
>
> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>

This looks good to me. Just two small bits I overlooked during the first 
review, sorry for that.

> +};
> +
> [...]
> +static int tmp117_read_raw(struct iio_dev *indio_dev,
> +		struct iio_chan_spec const *channel, int *val,
> +		int *val2, long mask)
> +{
> +	struct tmp117_data *data = iio_priv(indio_dev);
> +	u16 tmp, off;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		tmp = tmp117_read_reg(data, TMP117_REG_TEMP);
> +		*val = tmp;
No need for tmp here. Just directly assign to val.
> +		return IIO_VAL_INT;
> +
> +	case IIO_CHAN_INFO_CALIBBIAS:
> +		off = tmp117_read_reg(data, TMP117_REG_TEMP_OFFSET);
> +		*val = ((int16_t)off * (int32_t)TMP117_RESOLUTION) / 10000000;
> +		*val2 = ((int16_t)off * (int32_t)TMP117_RESOLUTION) % 10000000;
> +		return IIO_VAL_INT_PLUS_MICRO;
> +
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = 0;
> +		*val2 = TMP117_SCALE;
> +		return IIO_VAL_INT_PLUS_NANO;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int tmp117_write_raw(struct iio_dev *indio_dev,
> +		struct iio_chan_spec const *channel, int val,
> +		int val2, long mask)
> +{
> +	struct tmp117_data *data = iio_priv(indio_dev);
> +	u16 off;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_CALIBBIAS:
> +		off = ((val * 10000000) + (val2 * 10))
> +						/ (int32_t)TMP117_RESOLUTION;

This needs some input validation. Writing a too large or too small value 
will cause an overflow/underflow and a bogus value will be written to 
the register.

You can either reject invalid values by returning -EINVAL or clamp them 
into the right range. Up to you how you want to handle this.

> +		return tmp117_write_reg(data, TMP117_REG_TEMP_OFFSET, off);
> +
> +	default:
> +		return -EINVAL;
> +	}
> +}