[PATCH] iio: Handle enumerated properties with gaps

[Lars-Peter Clausen <lars@metafoo.de>]

Some enums might have gaps or reserved values in the middle of their value
range. E.g. consider a 2-bit enum where the values 0, 1 and 3 have a
meaning, but 2 is a reserved value and must not be used.

Add support for such enums to the IIO enum helper functions. A reserved
value is marked by setting its entry in the items array to NULL rather
than the normal descriptive string value.

Unfortunately that means we can no longer use __sysfs_match_string() since
it treats a NULL entry as the array terminator. But the amount of
boilerplate is manageable.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
---
Open for suggestions on how to massage __sysfs_match_string() into handling
this use-case.
---
 drivers/iio/industrialio-core.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 2e8e36f9da61..e69bef13d005 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -446,8 +446,12 @@ ssize_t iio_enum_available_read(struct iio_dev *indio_dev,
 	if (!e->num_items)
 		return 0;
 
-	for (i = 0; i < e->num_items; ++i)
+	for (i = 0; i < e->num_items; ++i) {
+		if (!e->items[i])
+			continue;
+
 		len += scnprintf(buf + len, PAGE_SIZE - len, "%s ", e->items[i]);
+	}
 
 	/* replace last space with a newline */
 	buf[len - 1] = '\n';
@@ -468,7 +472,7 @@ ssize_t iio_enum_read(struct iio_dev *indio_dev,
 	i = e->get(indio_dev, chan);
 	if (i < 0)
 		return i;
-	else if (i >= e->num_items)
+	else if (i >= e->num_items || !e->items[i])
 		return -EINVAL;
 
 	return snprintf(buf, PAGE_SIZE, "%s\n", e->items[i]);
@@ -480,16 +484,21 @@ ssize_t iio_enum_write(struct iio_dev *indio_dev,
 	size_t len)
 {
 	const struct iio_enum *e = (const struct iio_enum *)priv;
+	unsigned int i;
 	int ret;
 
 	if (!e->set)
 		return -EINVAL;
 
-	ret = __sysfs_match_string(e->items, e->num_items, buf);
-	if (ret < 0)
-		return ret;
+	for (i = 0; i < e->num_items; i++) {
+		if (e->items[i] && sysfs_streq(buf, e->items[i]))
+			break;
+	}
+
+	if (i == e->num_items)
+		return -EINVAL;
 
-	ret = e->set(indio_dev, chan, ret);
+	ret = e->set(indio_dev, chan, i);
 	return ret ? ret : len;
 }
 EXPORT_SYMBOL_GPL(iio_enum_write);
-- 
2.11.0