[RFC PATCH v2 1/5] iio: core: Point users of extend_name field to read_label callback

[Marijn Suijten]

As mentioned and discussed in [1] extend_name should not be used for
full channel labels (and most drivers seem to only use it to express a
short type of a channel) as this affects sysfs filenames, while the
label name is supposed to be extracted from the *_label sysfs file
instead.  This appears to have been unclear to some drivers as
extend_name is also used when read_label is unset, achieving an initial
goal of providing sensible names in *_label sysfs files without noticing
that sysfs filenames are (negatively and likely unintentionally)
affected as well.

Point readers of iio_chan_spec::extend_name to iio_info::read_label by
mentioning deprecation and side-effects of this field.

[1]: https://lore.kernel.org/linux-arm-msm/20221221223432.si2aasbleiicayfl@xxxxxxxxxxxxxx/

Suggested-by: Jonathan Cameron <jic23@xxxxxxxxxx>
Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
---
 include/linux/iio/iio.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 81413cd3a3e7..36c89f238fb9 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -221,6 +221,9 @@ struct iio_event_spec {
  * @extend_name:	Allows labeling of channel attributes with an
  *			informative name. Note this has no effect codes etc,
  *			unlike modifiers.
+ *			This field is deprecated in favour of overriding read_label
+ *			in iio_info, which unlike @extend_name does not affect sysfs
+ *			filenames.
  * @datasheet_name:	A name used in in-kernel mapping of channels. It should
  *			correspond to the first name that the channel is referred
  *			to by in the datasheet (e.g. IND), or the nearest
-- 
2.39.0