linux-kernel - Re: [PATCH 6/7] hwmon: iio: Add min/max support

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Message-ID: <099a8ce2-0837-4d79-8e58-8f7af0a0ff7d@linux.dev>
Date: Mon, 28 Jul 2025 18:32:43 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>,
 linux-iio@...r.kernel.org, linux-hwmon@...r.kernel.org,
 Andy Shevchenko <andy@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, linux-kernel@...r.kernel.org,
 David Lechner <dlechner@...libre.com>
Subject: Re: [PATCH 6/7] hwmon: iio: Add min/max support

On 7/27/25 12:35, Jonathan Cameron wrote:
> On Mon, 14 Jul 2025 21:20:22 -0400
> Sean Anderson <sean.anderson@...ux.dev> wrote:
> 
>> Add support for minimum/maximum attributes. Like the _input attribute,
>> we just need to call into the IIO API.
>> 
>> Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
> 
> Similar comments to previous. I'm not keen on the blend of allocation of
> attributes and registration.  If we can break that link I think it will give
> cleaner code.
>
>>  static int add_device_attr(struct device *dev, struct iio_hwmon_state *st,
>>  			   ssize_t (*show)(struct device *dev,
>>  					   struct device_attribute *attr,
>> @@ -123,6 +171,40 @@ static int add_device_attr(struct device *dev, struct iio_hwmon_state *st,
>>  	return 0;
>>  }
>>  
>> +static int add_event_attr(struct device *dev, struct iio_hwmon_state *st,
>> +			  int i, enum iio_event_direction dir,
>> +			  const char *fmt, ...)
>> +{
>> +	struct sensor_device_attribute_2 *a;
>> +	umode_t mode;
>> +	va_list ap;
>> +
>> +	mode = iio_event_mode(&st->channels[i], IIO_EV_TYPE_THRESH, dir,
>> +			      IIO_EV_INFO_VALUE);
>> +	if (!mode)
>> +		return 0;
>> +
>> +	a = devm_kzalloc(dev, sizeof(*a), GFP_KERNEL);
>> +	if (!a)
>> +		return -ENOMEM;
>> +
>> +	sysfs_attr_init(&a->dev_attr.attr);
>> +	va_start(ap, fmt);
>> +	a->dev_attr.attr.name = devm_kvasprintf(dev, GFP_KERNEL, fmt, ap);
>> +	va_end(ap);
>> +	if (!a->dev_attr.attr.name)
>> +		return -ENOMEM;
>> +
>> +	a->dev_attr.show = iio_hwmon_read_event;
>> +	a->dev_attr.store = iio_hwmon_write_event;
>> +	a->dev_attr.attr.mode = mode;
>> +	a->index = i;
>> +	a->nr = dir;
>> +
>> +	st->attrs[st->num_attrs++] = &a->dev_attr.attr;
> similar comment to the previous, though here I think we'd
> need to pass in the channel to an iio_hwmon_alloc_event_attr() as ideally we'd
> not be messing with st at all in here.  So maybe it doesn't work out.

Well, I used to have

+               if (iio_read_channel_label(&st->channels[i], buf) >= 0) {
+                       st->attrs[attr] = create_attr(dev, iio_hwmon_read_label,
+                                                     NULL, 0444, i, 0, 0, 0,
+                                                     "%s%d_label", prefix, n);
+                       if (!st->attrs[attr++])
+                               return -ENOMEM;
+               }

but even with a shorter function name, all the parameters are starting
to get bunched up on the right side. And if we make it longer as you
propose it starts looking like


+               if (iio_read_channel_label(&st->channels[i], buf) >= 0) {
+                       st->attrs[attr] =
+                               iio_hwmon_create_device_attr(dev,
+                                                            iio_hwmon_read_label,
+                                                            NULL, 0444, i, 0, 0,
+                                                            0, "%s%d_label",
+                                                            prefix, n);
+                       if (!st->attrs[attr++])
+                               return -ENOMEM;
+               }

which is IMO really terrible-looking.

Maybe we should just stick everything in an xarray and linearize it at
the end of probe...

--Sean