Re: [PATCH v8 06/17] iio: core: create local __iio_chan_prefix_emit() for reuse

On Tue, Jul 14, 2026 at 12:02:46PM +0100, Rodrigo Alencar via B4 Relay wrote:

> Move logic to create a channel prefix for naming attribute files into a
> separate __iio_chan_prefix_emit() function for reuse. The dev pointer is
> passed to __iio_device_attr_init() so that dev_err() replaces WARN().
> The new helper is going to be used to expose channel relationships as
> sysfs attributes.

...

> +static ssize_t __iio_chan_prefix_emit(struct device *dev,
> +				      const struct iio_chan_spec *chan,
> +				      enum iio_shared_by shared_by,
> +				      char *buf, size_t len)
> +{
> +	const char *type = iio_chan_type_name_spec[chan->type];
> +	const char *dir = iio_direction[chan->output];
> +	struct seq_buf s;
> +
> +	seq_buf_init(&s, buf, len);
> +
> +	switch (shared_by) {
> +	case IIO_SHARED_BY_ALL:
> +		break;
> +	case IIO_SHARED_BY_DIR:
> +		seq_buf_printf(&s, "%s", dir);
> +		break;
> +	case IIO_SHARED_BY_TYPE:
> +		seq_buf_printf(&s, "%s_%s", dir, type);
> +		if (chan->differential)
> +			seq_buf_printf(&s, "-%s", type);
> +		break;
> +	case IIO_SEPARATE:

> +		seq_buf_printf(&s, "%s_%s", dir, type);
> +		if (chan->indexed) {
> +			seq_buf_printf(&s, "%d", chan->channel);
> +			if (chan->differential)
> +				seq_buf_printf(&s, "-%s%d", type, chan->channel2);
> +		} else if (chan->differential) {
> +			dev_err(dev, "Differential channels must be indexed\n");
> +			return -EINVAL;
> +		}
> +
> +		if (chan->modified) {
> +			if (chan->differential) {
> +				dev_err(dev, "Differential channels can not have modifier\n");
> +				return -EINVAL;
> +			}
> +			seq_buf_printf(&s, "_%s", iio_modifier_names[chan->channel2]);
> +		}
> +
> +		if (chan->extend_name)
> +			seq_buf_printf(&s, "_%s", chan->extend_name);
> +		break;

Can we actually do the validation first without dirtying the output?

		/* Validate differential channel settings */
		if (chan->differential) {
			if (!chan->indexed) {
				dev_err(dev, "Differential channels must be indexed\n");
				return -EINVAL;
			}
			if (chan->modified) {
				dev_err(dev, "Differential channels can not have modifier\n");
				return -EINVAL;
			}
		}

		seq_buf_printf(&s, "%s_%s", dir, type);

		if (chan->indexed) {
			seq_buf_printf(&s, "%d", chan->channel);

		if (chan->differential)
			seq_buf_printf(&s, "-%s%d", type, chan->channel2);

		if (chan->modified)
			seq_buf_printf(&s, "_%s", iio_modifier_names[chan->channel2]);

		if (chan->extend_name)
			seq_buf_printf(&s, "_%s", chan->extend_name);
		break;


> +	}
> +
> +	return seq_buf_has_overflowed(&s) ? -EOVERFLOW : s.len;
> +}

-- 
With Best Regards,
Andy Shevchenko