[PATCH v4] iio: Handle enumerated properties with gaps

[Alexandru Ardelean]

From: Lars-Peter Clausen <lars@xxxxxxxxxx>

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 can not be used.

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

Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---

Nearly 1 year and a half since I last touched this:
https://lore.kernel.org/linux-iio/20190508111913.7276-3-alexandru.ardelean@xxxxxxxxxx/

I tried a few shots at working with 'lib/string.c', and that went
slow. The __sysfs_match_string_with_gaps() approach has stalled.
https://lore.kernel.org/linux-iio/20190422140251.8960-1-alexandru.ardelean@xxxxxxxxxx/

I also tried to update the __sysfs_match_string() implementation based
on what the docstring said,
https://lore.kernel.org/lkml/20200212144723.21884-1-alexandru.ardelean@xxxxxxxxxx/

but then I just fixed the docstring to match
what the behavior does:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next-history.git/commit/lib/string.c?id=c11d3fa0116a6bc832a9e387427caa16f8de5ef2

In the end, for this patch, it means expanding the
__sysfs_match_string() helper.

 drivers/iio/industrialio-core.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index e9ee9363fed0..a88494066811 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -470,8 +470,11 @@ 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';
@@ -492,7 +495,7 @@ 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]);
@@ -504,16 +507,21 @@ 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);
-- 
2.17.1