linux-kernel - Re: [PATCH v2 2/2] hwmon: iio: Add labels from IIO channels

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Date: Mon, 24 Jun 2024 11:47:39 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Sean Anderson <sean.anderson@...ux.dev>,
 Jonathan Cameron <jic23@...nel.org>, Jean Delvare <jdelvare@...e.com>,
 linux-iio@...r.kernel.org, linux-hwmon@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH v2 2/2] hwmon: iio: Add labels from IIO channels

On 6/24/24 10:46, Sean Anderson wrote:
> Add labels from IIO channels to our channels. This allows userspace to
> display more meaningful names instead of "in0" or "temp5".
> 
> Although lm-sensors gracefully handles errors when reading channel
> labels, the ABI says the label attribute
> 
>> Should only be created if the driver has hints about what this voltage
>> channel is being used for, and user-space doesn't.
> 
> Therefore, we test to see if the channel has a label before
> creating the attribute.
> 

FWIW, complaining about an ABI really does not belong into a commit
message. Maybe you and lm-sensors don't care about error returns when
reading a label, but there are other userspace applications which may
expect drivers to follow the ABI. Last time I checked, the basic rule
was still "Don't break userspace", and that doesn't mean "it's ok to
violate / break an ABI as long as no one notices".

> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> ---
> 
> Changes in v2:
> - Check if the label exists before creating the attribute
> 
>   drivers/hwmon/iio_hwmon.c | 45 ++++++++++++++++++++++++++++++++++-----
>   1 file changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/hwmon/iio_hwmon.c b/drivers/hwmon/iio_hwmon.c
> index 4c8a80847891..5722cb9d81f9 100644
> --- a/drivers/hwmon/iio_hwmon.c
> +++ b/drivers/hwmon/iio_hwmon.c
> @@ -33,6 +33,17 @@ struct iio_hwmon_state {
>   	struct attribute **attrs;
>   };
>   
> +static ssize_t iio_hwmon_read_label(struct device *dev,
> +				  struct device_attribute *attr,
> +				  char *buf)
> +{
> +	struct sensor_device_attribute *sattr = to_sensor_dev_attr(attr);
> +	struct iio_hwmon_state *state = dev_get_drvdata(dev);
> +	struct iio_channel *chan = &state->channels[sattr->index];
> +
> +	return iio_read_channel_label(chan, buf);
> +}
> +

I personally find it a bit kludgy that an in-kernel API would do a
sysfs write like this and expect a page-aligned buffer as parameter,
but since Jonathan is fine with it:

Acked-by: Guenter Roeck <linux@...ck-us.net>

Jonathan, please apply through your tree.

Thanks,
Guenter