[PATCH v2 net-next 07/12] net: ethtool: add helpers for MM addFragSize translation

[Vladimir Oltean]

We deliberately make the Linux UAPI pass the additional fragment size in
octets, even though IEEE 802.3 defines it as discrete values, and
addFragSize is just the multiplier. This is because there is nothing
impossible in operating with an in-between value for the fragment size
of non-final preempted fragments, and there may even appear hardware
which supports the in-between sizes.

For the hardware which just understands addFragSize as being a
multiplier, create two helpers which translate back and forth the values
passed in octets.

Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
v1->v2: patch is new

 include/linux/ethtool.h | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 01b1e34dc30e..1c3e8fc53609 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -979,6 +979,45 @@ void ethtool_aggregate_pause_stats(struct net_device *dev,
 void ethtool_aggregate_rmon_stats(struct net_device *dev,
 				  struct ethtool_rmon_stats *rmon_stats);
 
+/**
+ * ethtool_mm_add_frag_size_std_to_oct - Translate standard add_frag_size into
+ *	value in octets
+ * @val_std: Value of addFragSize variable in octets
+ */
+static inline u32 ethtool_mm_add_frag_size_std_to_oct(u32 val_std)
+{
+	return 64 * (1 + val_std) - 4;
+}
+
+/**
+ * ethtool_mm_add_frag_size_oct_to_std - Translate add_frag_size into
+ *	standard value
+ * @val_oct: Value of addFragSize variable in octets
+ * @val_std: Pointer where the standard addFragSize value is to be returned
+ * @extack: Netlink extended ack
+ *
+ * Translate a value in octets to one of 0, 1, 2, 3 according to the reverse
+ * application of the 802.3 formula 64 * (1 + addFragSize) - 4. To be called
+ * by drivers which do not support programming addFragSize to a continuous
+ * range. Returns error on other fragment length values.
+ */
+static inline int ethtool_mm_add_frag_size_oct_to_std(u32 val_oct, u32 *val_std,
+						      struct netlink_ext_ack *extack)
+{
+	u32 add_frag_size;
+
+	for (add_frag_size = 0; add_frag_size < 4; add_frag_size++) {
+		if (ethtool_mm_add_frag_size_std_to_oct(add_frag_size) == val_oct) {
+			*val_std = add_frag_size;
+			return 0;
+		}
+	}
+
+	NL_SET_ERR_MSG_MOD(extack,
+			   "addFragSize required to be one of 60, 124, 188 or 252");
+	return -EINVAL;
+}
+
 /**
  * ethtool_sprintf - Write formatted string to ethtool string data
  * @data: Pointer to start of string to update
-- 
2.34.1