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Date: Fri, 11 Jun 2021 18:50:10 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Paul Cercueil <paul@...pouillou.net>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <michael.hennerich@...log.com>,
linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: core: Add "extended_name" attribute to all
channels
On Thu, 10 Jun 2021 15:49:58 +0100
Paul Cercueil <paul@...pouillou.net> wrote:
> Le jeu., juin 10 2021 at 15:34:25 +0100, Jonathan Cameron
> <Jonathan.Cameron@...wei.com> a écrit :
> > On Thu, 10 Jun 2021 13:45:56 +0100
> > Paul Cercueil <paul@...pouillou.net> 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?
Not yet and if we add a check as part of your series we can stop it
happening in future. Simple checking for the read_label callback
should be enough.
>
> 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').
That would be great!
Jonathan
>
> -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@...pouillou.net>
> >> ---
> >> 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++) {
> >
>
>
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