Re: [PATCH 2/2] iio: temperature: Add MCP9600 thermocouple EMF converter

[Lars-Peter Clausen <lars@metafoo.de>]

This looks really good. I have some small comments, and I apologize for 
only having them so late in the review cycle.

On 3/19/23 11:47, Andrew Hepp wrote:
> Add support for the MCP9600 thermocouple EMF converter.

Would be nice to have a very short description of the capabilities of 
the sensor in the commit message.

>
> Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/MCP960X-Data-Sheet-20005426.pdf
> Signed-off-by: Andrew Hepp <andrew.hepp@ahepp.dev>
> ---
> [...]
> diff --git a/drivers/iio/temperature/mcp9600.c b/drivers/iio/temperature/mcp9600.c
> new file mode 100644
> index 000000000000..b6d8ffb90c36
> --- /dev/null
> +++ b/drivers/iio/temperature/mcp9600.c
> @@ -0,0 +1,145 @@
> +// SPDX-License-Identifier: GPL-2.0+
> [...]
> +static const struct iio_chan_spec mcp9600_channels[] = {
> +	{
> +		.type = IIO_TEMP,
> +		.address = MCP9600_HOT_JUNCTION,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +	{
> +		.type = IIO_TEMP,
> +		.address = MCP9600_COLD_JUNCTION,
> +		.channel2 = IIO_MOD_TEMP_AMBIENT,
> +		.modified = 1,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +	IIO_CHAN_SOFT_TIMESTAMP(2),
If you do not have supported for buffered capture there is no need to 
include a timestamp in the channel spec. There is no way to read it 
without buffered support.
> +};
> +
> +struct mcp9600_data {
> +	struct i2c_client *client;
> +	struct mutex read_lock; /* lock to prevent concurrent reads */
> +};
> +
> +static int mcp9600_read(struct mcp9600_data *data,
> +			struct iio_chan_spec const *chan, int *val)
> +{
> +	__be16 buf;
buf does not seem to be used.
> +	int ret;
> +
> +	mutex_lock(&data->read_lock);
Do you actually need the custom lock? i2c_smbus_read_word_swapped itself 
should provide locking and there is only a single operation under your 
custom lock, which will already be atomic.
> +	ret = i2c_smbus_read_word_swapped(data->client, chan->address);
> +	mutex_unlock(&data->read_lock);
> +
> +	if (ret < 0)
> +		return ret;
> +	*val = ret;
> +
> +	return 0;
> +}
> +
> [...]
> +static int mcp9600_probe(struct i2c_client *client)
> +{
> +	struct iio_dev *indio_dev;
> +	struct mcp9600_data *data;
> +	int ret;
> +
> +	ret = i2c_smbus_read_byte_data(client, MCP9600_DEVICE_ID);
> +	if (ret < 0)
> +		return ret;

Might as well throw an error message in here for better diagnostics.

     return dev_err_probe(&client->dev, ret, "Failed to read device ID\n");