Re: [PATCH 2/2] iio: core: Add "extended_name" attribute to all channels

[Paul Cercueil <paul@xxxxxxxxxxxxxxx>]

Le jeu., juin 10 2021 at 15:34:25 +0100, Jonathan Cameron 
<Jonathan.Cameron@xxxxxxxxxx> a écrit :
> On Thu, 10 Jun 2021 13:45:56 +0100
> Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
>
> >  The point of this new attribute is to make the IIO tree actually
> >  parsable.
> >
> >  Before, given this attribute as a filename:
> >  in_voltage0_aux_sample_rate
> >
> >  Userspace had no way to know if the attribute name was
> >  "aux_sample_rate" with no extended name, or "sample_rate" with 
> > "aux" as
> >  the extended name, or just "rate" with "aux_sample" as the extended
> >  name.
> >
> >  This was somewhat possible to deduce when there was more than one
> >  attribute present for a given channel, e.g:
> >  in_voltage0_aux_sample_rate
> >  in_voltage0_aux_frequency
> >
> >  There, it was possible to deduce that "aux" was the extended name. 
> > But
> >  even with more than one attribute, this wasn't very robust, as two
> >  attributes starting with the same prefix (e.g. "sample_rate" and
> >  "sample_size") would result in the first part of the prefix being
> >  interpreted as being part of the extended name.
> >
> >  To address this issue, add an "extended_name" attribute to all 
> > channels
> >  that actually do have an extended name.
>
> Change the patch title to make it clear that it only applies to those
> that have extended_name set.
>
> >  For this attribute, the extended
> >  name is not present in the filename; so in this example, the file 
> > name
> >  would be "in_voltage0_extended_name", and reading it would return 
> > "aux".
>
> Ah. Now I see the slightly issue with my immediate thought that we 
> should
> just put this in the label attribute (and not allow both extended_name
> and label to be provided).

Are there cases where extended_name and label are both used?

If they are exclusive, then it would be fine to put it in the label 
attribute. Parsing would be a bit more awkward because of the extended 
name but still possible (e.g. libiio would read 'in_voltage0_foo_label' 
and check that it returns 'foo').

-Paul

> Hmm. It's a bit ugly but given it hopefully doesn't effect that many 
> drivers
> I could probably live with it.
>
> However, needs a patch to Documentation/ABI/testing/sysfs-bus-iio
> and a clear statement that this is for backwards compatibility 
> reasons.
> I don't want to see extended_name getting added to new drivers!
>
> Jonathan
>
> >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> >  ---
> >   drivers/iio/industrialio-core.c | 41 
> > +++++++++++++++++++++++++++++++++
> >   1 file changed, 41 insertions(+)
> >
> >  diff --git a/drivers/iio/industrialio-core.c 
> > b/drivers/iio/industrialio-core.c
> >  index ec34d930920c..4cdf9f092d73 100644
> >  --- a/drivers/iio/industrialio-core.c
> >  +++ b/drivers/iio/industrialio-core.c
> >  @@ -723,6 +723,16 @@ static ssize_t iio_read_channel_label(struct 
> > device *dev,
> >   	return indio_dev->info->read_label(indio_dev, this_attr->c, buf);
> >   }
> >
> >  +static ssize_t iio_read_channel_extended_name(struct device *dev,
> >  +					      struct device_attribute *attr,
> >  +					      char *buf)
> >  +{
> >  +	const struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
> >  +	const struct iio_chan_spec *chan = this_attr->c;
> >  +
> >  +	return sprintf(buf, "%s\n", chan->extend_name);
> >  +}
> >  +
> >   static ssize_t iio_read_channel_info(struct device *dev,
> >   				     struct device_attribute *attr,
> >   				     char *buf)
> >  @@ -1185,6 +1195,32 @@ static int 
> > iio_device_add_channel_label(struct iio_dev *indio_dev,
> >   	return 1;
> >   }
> >
> >  +static int
> >  +iio_device_add_channel_extended_name(struct iio_dev *indio_dev,
> >  +				     struct iio_chan_spec const *chan)
> >  +{
> >  +	struct iio_dev_opaque *iio_dev_opaque = 
> > to_iio_dev_opaque(indio_dev);
> >  +	int ret;
> >  +
> >  +	if (!chan->extend_name)
> >  +		return 0;
> >  +
> >  +	ret = __iio_add_chan_devattr("extended_name",
> >  +				     chan,
> >  +				     &iio_read_channel_extended_name,
> >  +				     NULL,
> >  +				     0,
> >  +				     IIO_SEPARATE,
> >  +				     &indio_dev->dev,
> >  +				     NULL,
> >  +				     &iio_dev_opaque->channel_attr_list,
> >  +				     false);
> >  +	if (ret < 0)
> >  +		return ret;
> >  +
> >  +	return 1;
> >  +}
> >  +
> >   static int iio_device_add_info_mask_type(struct iio_dev *indio_dev,
> >   					 struct iio_chan_spec const *chan,
> >   					 enum iio_shared_by shared_by,
> >  @@ -1327,6 +1363,11 @@ static int 
> > iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
> >   		return ret;
> >   	attrcount += ret;
> >
> >  +	ret = iio_device_add_channel_extended_name(indio_dev, chan);
> >  +	if (ret < 0)
> >  +		return ret;
> >  +	attrcount += ret;
> >  +
> >   	if (chan->ext_info) {
> >   		unsigned int i = 0;
> >   		for (ext_info = chan->ext_info; ext_info->name; ext_info++) {