[net-next PATCH v3 1/3] net: phy: refactor and better document phy_speeds function

[Christian Marangi <ansuelsmth@gmail.com>]

Refactor the phy_speeds function to be more readable and understandable
and add some documentation on it.

While on it extend it to take NULL speeds values to make it return only
the count of speed modes in the passed mask.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 drivers/net/phy/phy-core.c | 50 ++++++++++++++++++++++++++++++++++----
 1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/drivers/net/phy/phy-core.c b/drivers/net/phy/phy-core.c
index 966c93cbe616..9618d89458d1 100644
--- a/drivers/net/phy/phy-core.c
+++ b/drivers/net/phy/phy-core.c
@@ -317,17 +317,57 @@ phy_lookup_setting(int speed, int duplex, const unsigned long *mask, bool exact)
 }
 EXPORT_SYMBOL_GPL(phy_lookup_setting);
 
+/**
+ * phy_speeds - return all speeds in mask
+ * @speeds: pointer to array where to put the speed modes
+ * @size: size of array where to put the speed modes
+ * @mask: mask of speed modes to compare with
+ *
+ * Take mask, test bit in mask with the settings table and compose the
+ * speeds array based on that as many as size permits.
+ *
+ * With speeds NULL, only the number of detected modes is returned and
+ * no array is composed. (size value is ignored)
+ *
+ * Return the number of detected modes in mask.
+ */
 size_t phy_speeds(unsigned int *speeds, size_t size,
 		  unsigned long *mask)
 {
+	unsigned int curr_speed;
 	size_t count;
 	int i;
 
-	for (i = 0, count = 0; i < ARRAY_SIZE(settings) && count < size; i++)
-		if (settings[i].bit < __ETHTOOL_LINK_MODE_MASK_NBITS &&
-		    test_bit(settings[i].bit, mask) &&
-		    (count == 0 || speeds[count - 1] != settings[i].speed))
-			speeds[count++] = settings[i].speed;
+	for (i = 0, count = 0; i < ARRAY_SIZE(settings); i++) {
+		/* Inconsistent mapping with ethtool modes? */
+		if (unlikely(settings[i].bit >= __ETHTOOL_LINK_MODE_MASK_NBITS))
+			return count;
+
+		/* Skip. Speed not in provided mask */
+		if (!test_bit(settings[i].bit, mask))
+			continue;
+
+		/* settings struct is set in descending order with
+		 * ordered speed modes. Detect a new speed mode by
+		 * checking if it's different than the current one.
+		 */
+		if (count == 0 || curr_speed != settings[i].speed) {
+			curr_speed = settings[i].speed;
+
+			/* With speeds not declared, we return only
+			 * the number of detected speed mode in the mask.
+			 */
+			if (speeds) {
+				/* No more space to put new modes */
+				if (count > size)
+					return count;
+
+				speeds[count] = curr_speed;
+			}
+
+			count++;
+		}
+	}
 
 	return count;
 }
-- 
2.40.1