Re: [PATCH v9 08/17] iio: core: add hierarchical channel relationships

[Rodrigo Alencar]

On 25/07/26 23:24, Jonathan Cameron wrote:
> On Wed, 22 Jul 2026 16:50:17 +0100
> Rodrigo Alencar via B4 Relay <devnull+rodrigo.alencar.analog.com@xxxxxxxxxx> wrote:
> 
> > From: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>
> > 
> > Add parent-child relationship between iio channels by creating a parent
> > pointer field in iio_chan_spec struct and exposing a sysfs attribute that
> > returns the parent channel prefix.
> > 
> > Signed-off-by: Rodrigo Alencar <rodrigo.alencar@xxxxxxxxxx>
> Hi Rodrigo.
> 
> One small thing below
> 
> Jonathan
> 
> > ---
> >  drivers/iio/industrialio-core.c | 40 ++++++++++++++++++++++++++++++++++++++++
> >  include/linux/iio/iio.h         |  5 +++++
> >  2 files changed, 45 insertions(+)
> > 
> > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > index aa9d6474edd9..f7e3048354b9 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -856,6 +856,22 @@ static ssize_t iio_read_channel_label(struct device *dev,
> >  					 to_iio_dev_attr(attr)->c, buf);
> >  }
> >  
> > +static ssize_t iio_read_channel_parent(struct device *dev,
> > +				       struct device_attribute *attr,
> > +				       char *buf)
> > +{
> > +	const struct iio_chan_spec *chan = to_iio_dev_attr(attr)->c->parent;
> > +	ssize_t len;
> > +
> > +	len = __iio_chan_prefix_emit(dev, chan, IIO_SEPARATE, buf, PAGE_SIZE);
> > +	if (len < 0)
> > +		return len;
> > +
> > +	buf[len++] = '\n';
> 
> Use sysfs_emit_at() for this rather than a direct write. I'd rather not have
> to think about what happens if __iio_chan_prefix_emit() returns exactly
> PAGE_SIZE().

We can have __iio_chan_prefix_emit() called with PAGE_SIZE - 1?

Filenames should be capped at 255.. so that NAME_MAX << PAGE_SIZE 

As you suggest, we need a local buffer. Not sure we need to do an extra copy...
 
> > +
> > +	return len;
> > +}
> > +

-- 
Kind regards,

Rodrigo Alencar