RE: [RFC PATCH v2] iio: core: Add optional symbolic label to a device channel

["Pop, Cristian" <Cristian.Pop@analog.com>]

Best ragards,
Cristian Pop

> -----Original Message-----
> From: Jonathan Cameron <jic23@kernel.org>
> Sent: Sunday, August 30, 2020 2:24 PM
> To: Pop, Cristian <Cristian.Pop@analog.com>
> Cc: linux-iio@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [RFC PATCH v2] iio: core: Add optional symbolic label to a device
> channel
> 
> [External]
> 
> On Mon, 24 Aug 2020 11:36:46 +0300
> Cristian Pop <cristian.pop@analog.com> wrote:
> 
> > If a label is defined in the device tree for this channel add that to
> > the channel specific attributes. This is useful for userspace to be
> > able to identify an individual channel.
> >
> > Signed-off-by: Cristian Pop <cristian.pop@analog.com>
> > ---
> >  Changes in v2:
> > 	- Move label check before "read_raw" callback.
> > 	- Move the responsability to of parsing channel labels, to the
> > 	  driver.
> >
> >  drivers/iio/industrialio-core.c | 10 ++++++++--
> >  include/linux/iio/iio.h         |  2 ++
> >  include/linux/iio/types.h       |  1 +
> >  3 files changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iio/industrialio-core.c
> > b/drivers/iio/industrialio-core.c index 1527f01a44f1..32277e94f02d
> > 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -135,6 +135,7 @@ static const char * const iio_modifier_names[] = {
> >  /* relies on pairs of these shared then separate */  static const
> > char * const iio_chan_info_postfix[] = {
> >  	[IIO_CHAN_INFO_RAW] = "raw",
> > +	[IIO_CHAN_INFO_LABEL] = "label",
> >  	[IIO_CHAN_INFO_PROCESSED] = "input",
> >  	[IIO_CHAN_INFO_SCALE] = "scale",
> >  	[IIO_CHAN_INFO_OFFSET] = "offset",
> > @@ -653,14 +654,18 @@ static ssize_t iio_read_channel_info(struct device
> *dev,
> >  	int ret;
> >  	int val_len = 2;
> >
> > -	if (indio_dev->info->read_raw_multi)
> > +	if (indio_dev->info->read_raw_multi) {
> >  		ret = indio_dev->info->read_raw_multi(indio_dev, this_attr-
> >c,
> >
> 	INDIO_MAX_RAW_ELEMENTS,
> >  							vals, &val_len,
> >  							this_attr->address);
> > -	else
> > +	} else {
> >  		ret = indio_dev->info->read_raw(indio_dev, this_attr->c,
> >  				    &vals[0], &vals[1], this_attr->address);
> > +		if (ret < 0 && this_attr->address == IIO_CHAN_INFO_LABEL
> &&
> > +			this_attr->c->label_name)
> 
> I'm not keen on this. We shouldn't be calling read_raw at all in this path.
> There is no way it can return a valid label.
> 
> > +			return sprintf(buf, "%s\n", this_attr->c->label_name);
> > +	}
> >
> >  	if (ret < 0)
> >  		return ret;
> > @@ -1399,6 +1404,7 @@ static int iio_device_register_sysfs(struct iio_dev
> *indio_dev)
> >  			attrcount_orig++;
> >  	}
> >  	attrcount = attrcount_orig;
> > +
> 
> Please avoid unrelated white space changes.
> 
> >  	/*
> >  	 * New channel registration method - relies on the fact a group does
> >  	 * not need to be initialized if its name is NULL.
> > diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h index
> > a1be82e74c93..39209f3b62be 100644
> > --- a/include/linux/iio/iio.h
> > +++ b/include/linux/iio/iio.h
> > @@ -223,6 +223,7 @@ struct iio_event_spec {
> >   *			correspond to the first name that the channel is
> referred
> >   *			to by in the datasheet (e.g. IND), or the nearest
> >   *			possible compound name (e.g. IND-INC).
> > + * @label_name:		Unique name to identify which channel this is.
> >   * @modified:		Does a modifier apply to this channel. What
> these are
> >   *			depends on the channel type.  Modifier is set in
> >   *			channel2. Examples are IIO_MOD_X for axial sensors
> about
> > @@ -260,6 +261,7 @@ struct iio_chan_spec {
> >  	const struct iio_chan_spec_ext_info *ext_info;
> >  	const char		*extend_name;
> >  	const char		*datasheet_name;
> > +	const char		*label_name;
> 
> This can't be part of chan_spec as that is constant in many drivers.
> We need a separate way of doing this.  Don't use info_mask, but register it
> separately for each channel in a similar way to we do the name and label
> attributes for the whole device.
> 
If "label_name" can't be part of the "struct iio_chan_spec " why would I pass
it to the callback function? Just identify the channel?
I would implement a callback :
int (*read_string)(struct iio_dev *indio_dev,
	const struct iio_chan_spec *chan, const char *buf, long info);
and use this callback for other purposes as well, not only for "label" attribute.

> I would add a new callback to iio_info that is passed the iio_chan_spec and
> returns a const char * for the label name.
> 
> The driver would be responsible for doing a lookup based on what it has
> cached from the dt parse, probably indexed off address or scan_index (that
> can be driver specific)
> 
> To create the attribute you need to add this to iio_device_register_sysfs and
> use the various core functions to build the attribute name in a similar fashion
> to that done for info mask elements.
> 
> It will be more complex than your approach, but make it more 'separable' as a
> feature in drivers.
> 
> Jonathan
> 
> 
> >  	unsigned		modified:1;
> >  	unsigned		indexed:1;
> >  	unsigned		output:1;
> > diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
> > index e6fd3645963c..c8f65f476eb2 100644
> > --- a/include/linux/iio/types.h
> > +++ b/include/linux/iio/types.h
> > @@ -34,6 +34,7 @@ enum iio_available_type {
> >
> >  enum iio_chan_info_enum {
> >  	IIO_CHAN_INFO_RAW = 0,
> > +	IIO_CHAN_INFO_LABEL,
> >  	IIO_CHAN_INFO_PROCESSED,
> >  	IIO_CHAN_INFO_SCALE,
> >  	IIO_CHAN_INFO_OFFSET,