staging:iio: Add extended IIO channel info

Sometimes devices have per channel properties which either do not map nicely to
the current channel info scheme (e.g. string properties) or are very device
specific, so it does not make sense to add generic support for them.

Currently drivers define these attributes by hand for each channel. Depending on
the number of channels this can amount to quite a few lines of boilerplate code.
Especially if a driver supports multiple variations of a chip with different
numbers of channels. In this case it becomes necessary to have a individual
attribute list per chip variation and also a individual iio_info struct.

This patch introduces a new scheme for handling such per channel attributes
called extended channel info attributes. A extended channel info attribute
consist of a name, a flag whether it is shared and read and write callbacks.
The read and write callbacks are similar to the {read,write}_raw callbacks and
take a IIO device and a channel as their first parameters, but instead of
pre-parsed integer values they directly get passed the raw string value, which
has been written to the sysfs file.

It is possible to assign a list of extended channel info attributes to a
channel. For each extended channel info attribute the IIO core will create a new
sysfs attribute conforming to the IIO channel naming spec for the channels type,
similar as for normal info attributes. Read and write access to this sysfs
attribute will be redirected to the extended channel info attributes read and
write callbacks.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 53 insertions, 0 deletions

diff --git a/drivers/staging/iio/industrialio-core.c b/drivers/staging/iio/industrialio-core.c
index 3a2d08026624..645bb45c89e8 100644
--- a/drivers/staging/iio/industrialio-core.c
+++ b/drivers/staging/iio/industrialio-core.c
@@ -144,6 +144,33 @@ static void __exit iio_exit(void)
 	bus_unregister(&iio_bus_type);
 }
 
+static ssize_t iio_read_channel_ext_info(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+	const struct iio_chan_spec_ext_info *ext_info;
+
+	ext_info = &this_attr->c->ext_info[this_attr->address];
+
+	return ext_info->read(indio_dev, this_attr->c, buf);
+}
+
+static ssize_t iio_write_channel_ext_info(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf,
+					 size_t len)
+{
+	struct iio_dev *indio_dev = dev_get_drvdata(dev);
+	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
+	const struct iio_chan_spec_ext_info *ext_info;
+
+	ext_info = &this_attr->c->ext_info[this_attr->address];
+
+	return ext_info->write(indio_dev, this_attr->c, buf, len);
+}
+
 static ssize_t iio_read_channel_info(struct device *dev,
 				     struct device_attribute *attr,
 				     char *buf)
@@ -423,6 +450,7 @@ static int iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
 					struct iio_chan_spec const *chan)
 {
 	int ret, i, attrcount = 0;
+	const struct iio_chan_spec_ext_info *ext_info;
 
 	if (chan->channel < 0)
 		return 0;
@@ -457,6 +485,31 @@ static int iio_device_add_channel_sysfs(struct iio_dev *indio_dev,
 			goto error_ret;
 		attrcount++;
 	}
+
+	if (chan->ext_info) {
+		unsigned int i = 0;
+		for (ext_info = chan->ext_info; ext_info->name; ext_info++) {
+			ret = __iio_add_chan_devattr(ext_info->name,
+					chan,
+					ext_info->read ?
+					    &iio_read_channel_ext_info : NULL,
+					ext_info->write ?
+					    &iio_write_channel_ext_info : NULL,
+					i,
+					ext_info->shared,
+					&indio_dev->dev,
+					&indio_dev->channel_attr_list);
+			i++;
+			if (ret == -EBUSY && ext_info->shared)
+				continue;
+
+			if (ret)
+				goto error_ret;
+
+			attrcount++;
+		}
+	}
+
 	ret = attrcount;
 error_ret:
 	return ret;