[PATCH AUTOSEL 5.4 14/20] net: mlx4: add SOF_TIMESTAMPING_TX_SOFTWARE flag when getting ts info

[Sasha Levin <sashal@kernel.org>]

From: Jason Xing <kernelxing@tencent.com>

[ Upstream commit b86bcfee30576b752302c55693fff97242b35dfd ]

As mlx4 has implemented skb_tx_timestamp() in mlx4_en_xmit(), the
SOFTWARE flag is surely needed when users are trying to get timestamp
information.

Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20250510093442.79711-1-kerneljasonxing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

Perfect! Now I can see that `skb_tx_timestamp(skb)` is called in the
`mlx4_en_xmit()` function, which is the main transmit function. This
confirms that the mlx4 driver does implement software timestamping. Now
let me compare this to the similar commits to see the pattern: **YES**
This commit should be backported to stable kernel trees. **Extensive
Explanation:** This commit addresses a clear inconsistency bug where the
mlx4 driver implements software timestamping functionality but fails to
advertise this capability to userspace through the ethtool timestamping
info interface. **Analysis of the fix:** 1. **The Problem**: The mlx4
driver calls `skb_tx_timestamp(skb)` in `mlx4_en_xmit()` at line 1091 of
`/drivers/net/ethernet/mellanox/mlx4/en_tx.c`, which means it properly
implements software TX timestamping. However, in
`mlx4_en_get_ts_info()`, it only advertises hardware timestamping
capabilities (`SOF_TIMESTAMPING_TX_HARDWARE`,
`SOF_TIMESTAMPING_RX_HARDWARE`, `SOF_TIMESTAMPING_RAW_HARDWARE`) but
omits the `SOF_TIMESTAMPING_TX_SOFTWARE` flag. 2. **The Fix**: The
change adds a single line `SOF_TIMESTAMPING_TX_SOFTWARE |` to the
`info->so_timestamping` field when hardware timestamping is supported,
correctly advertising both hardware and software timestamping
capabilities. 3. **Impact**: This is a user-facing API correctness
issue. Applications checking timestamping capabilities via ethtool would
incorrectly believe software timestamping is not supported, even though
the driver implements it. **Comparison with similar commits:** -
**Similar Commit #1 (YES)**: Also fixed a timestamping bug in mlx4,
showing these are important fixes - **Similar Commit #3 (YES)**: Fixed
incorrect timestamping capability reporting in mlx5 by removing false
software timestamping indication - **Similar Commit #5 (YES)**: Fixed
timestamping capabilities reporting using wrong BIT() macro in mlx5 The
pattern shows that timestamping capability reporting bugs are
consistently considered backport-worthy because they affect user-visible
API behavior. **Backport Criteria Assessment:** ✅ **Fixes a user-
affecting bug**: Applications cannot detect software timestamping
support ✅ **Small, contained change**: Single line addition with no
functional logic changes ✅ **No architectural changes**: Only fixes
capability reporting ✅ **Low regression risk**: Only adds a missing
flag, doesn't change driver behavior ✅ **Clear side effects**: None
beyond correctly advertising existing functionality ✅ **Follows stable
rules**: Important API correctness fix with minimal risk The fix is
identical in nature to Similar Commit #3 (marked YES) but in reverse -
where mlx5 removed false software timestamping advertisement, this adds
the missing software timestamping advertisement for mlx4 where it's
actually implemented.

 drivers/net/ethernet/mellanox/mlx4/en_ethtool.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c b/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
index b711148a9d503..9dbdd6266f731 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
@@ -1889,6 +1889,7 @@ static int mlx4_en_get_ts_info(struct net_device *dev,
 	if (mdev->dev->caps.flags2 & MLX4_DEV_CAP_FLAG2_TS) {
 		info->so_timestamping |=
 			SOF_TIMESTAMPING_TX_HARDWARE |
+			SOF_TIMESTAMPING_TX_SOFTWARE |
 			SOF_TIMESTAMPING_RX_HARDWARE |
 			SOF_TIMESTAMPING_RAW_HARDWARE;
 
-- 
2.39.5