Re: [PATCH v4 03/10] hwmon: (tmp421) add support for defining labels from DT

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Oct 12, 2021 at 11:27:14AM +0200, Krzysztof Adamski wrote:
> tmp42x is a multichannel temperature sensor with several external
> channels. Since those channels can be used to connect diodes placed
> anywhere in the system, their meaning will vary depending on the
> project. For this case, the hwmon framework has an idea of labels which
> allows us to assign the meaning to each channel.
> 
> The similar concept is already implemented in ina3221 - the label for
> each channel can be defined via device tree. See commit a9e9dd9c6de5
> ("hwmon: (ina3221) Read channel input source info from DT")
> 
> This patch adds support for similar feature to tmp421.
> 
> Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
> ---
>  drivers/hwmon/tmp421.c | 61 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/drivers/hwmon/tmp421.c b/drivers/hwmon/tmp421.c
> index 707310d616a4..ab64d9825ca4 100644
> --- a/drivers/hwmon/tmp421.c
> +++ b/drivers/hwmon/tmp421.c
> @@ -88,6 +88,7 @@ static const struct of_device_id __maybe_unused tmp421_of_match[] = {
>  MODULE_DEVICE_TABLE(of, tmp421_of_match);
>  
>  struct tmp421_channel {
> +	const char *label;
>  	s16 temp;
>  };
>  
> @@ -187,6 +188,16 @@ static int tmp421_read(struct device *dev, enum hwmon_sensor_types type,
>  
>  }
>  
> +static int tmp421_read_string(struct device *dev, enum hwmon_sensor_types type,
> +			     u32 attr, int channel, const char **str)
> +{
> +	struct tmp421_data *data = dev_get_drvdata(dev);
> +
> +	*str = data->channel[channel].label;
> +
> +	return 0;
> +}
> +
>  static umode_t tmp421_is_visible(const void *data, enum hwmon_sensor_types type,
>  				 u32 attr, int channel)
>  {
> @@ -194,6 +205,8 @@ static umode_t tmp421_is_visible(const void *data, enum hwmon_sensor_types type,
>  	case hwmon_temp_fault:
>  	case hwmon_temp_input:
>  		return 0444;
> +	case hwmon_temp_label:
> +		return 0444;
>  	default:
>  		return 0;
>  	}
> @@ -286,9 +299,53 @@ static int tmp421_detect(struct i2c_client *client,
>  	return 0;
>  }
>  
> +static int tmp421_probe_child_from_dt(struct i2c_client *client,
> +				      struct device_node *child,
> +				      struct tmp421_data *data)
> +
> +{
> +	struct device *dev = &client->dev;
> +	u32 i;
> +	int err;
> +
> +	err = of_property_read_u32(child, "reg", &i);
> +	if (err) {
> +		dev_err(dev, "missing reg property of %pOFn\n", child);
> +		return err;
> +	}
> +
> +	if (i >= MAX_CHANNELS) {

I think this needs to compare against data->channels. Otherwise, if
unsupported channels are listed in dt (say, reg==0x2 with tmp421),
we would end up with label attributes for those channels.

> +		dev_err(dev, "invalid reg %d of %pOFn\n", i, child);
> +		return -EINVAL;
> +	}
> +
> +	of_property_read_string(child, "label", &data->channel[i].label);
> +	if (data->channel[i].label)
> +		data->temp_config[i] |= HWMON_T_LABEL;
> +
> +	return 0;
> +}
> +
> +static int tmp421_probe_from_dt(struct i2c_client *client, struct tmp421_data *data)
> +{
> +	struct device *dev = &client->dev;
> +	const struct device_node *np = dev->of_node;
> +	struct device_node *child;
> +	int err;
> +
> +	for_each_child_of_node(np, child) {
> +		err = tmp421_probe_child_from_dt(client, child, data);
> +		if (err)
> +			return err;
> +	}
> +
> +	return 0;
> +}
> +
>  static const struct hwmon_ops tmp421_ops = {
>  	.is_visible = tmp421_is_visible,
>  	.read = tmp421_read,
> +	.read_string = tmp421_read_string,
>  };
>  
>  static int tmp421_probe(struct i2c_client *client)
> @@ -317,6 +374,10 @@ static int tmp421_probe(struct i2c_client *client)
>  	for (i = 0; i < data->channels; i++)
>  		data->temp_config[i] = HWMON_T_INPUT | HWMON_T_FAULT;
>  
> +	err = tmp421_probe_from_dt(client, data);
> +	if (err)
> +		return err;
> +
>  	data->chip.ops = &tmp421_ops;
>  	data->chip.info = data->info;
>