Add documentation explaining why the code which scans all available scan
masks is checking only a single long worth of bits even though the code
was intended to be supporting masks wider than single long.
Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
---
drivers/iio/industrialio-buffer.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 176d31d9f9d8..09c41e9ccf87 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -413,6 +413,22 @@ static const unsigned long *iio_scan_mask_match(const unsigned long *av_masks,
{
if (bitmap_empty(mask, masklength))
return NULL;
+ /*
+ * The condition here do not handle multi-long masks correctly.
+ * It only checks the first long to be zero, and will use such mask
+ * as a terminator even if there was bits set after the first long.
+ *
+ * Correct check would require using:
+ * while (!bitmap_empty(av_masks, masklength))
+ * instead. This is potentially hazardous because the
+ * avaliable_scan_masks is a zero terminated array of longs - and
+ * using the proper bitmap_empty() check for multi-long wide masks
+ * would require the array to be terminated with multiple zero longs -
+ * which is not such an usual pattern.
+ *
+ * As writing of this no multi-long wide masks were found in-tree, so
+ * the simple while (*av_masks) check is working.
+ */
while (*av_masks) {
if (strict) {
if (bitmap_equal(mask, av_masks, masklength))
--
2.41.0
--
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND
~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =]
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