[PATCH v3 net-next] amd-xgbe: Configure and retrieve 'tx-usecs' for Tx coalescing

[Vishal Badole <Vishal.Badole@amd.com>]

Ethtool has advanced with additional configurable options, but the
current driver does not support tx-usecs configuration using Ethtool.

Add support to configure and retrieve 'tx-usecs' using ethtool, which
specifies the wait time before servicing an interrupt for Tx coalescing.

Signed-off-by: Vishal Badole <Vishal.Badole@amd.com>
Acked-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
---
v2 -> v3:
    - Update the commit message.
    - Ensure tx-usecs value must be non zero.
    - Round tx-usecs to nearest multiple of jiffy granularity.
    - Link to v2: https://lore.kernel.org/netdev/20250812045035.3376179-1-Vishal.Badole@amd.com/

v1 -> v2:
    - Replace netdev_err() with extack interface for user error reporting.
    - Link to v1: https://lore.kernel.org/netdev/20250719072608.4048494-1-Vishal.Badole@amd.com/
---
 drivers/net/ethernet/amd/xgbe/xgbe-ethtool.c | 28 ++++++++++++++++++--
 drivers/net/ethernet/amd/xgbe/xgbe.h         |  1 +
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-ethtool.c b/drivers/net/ethernet/amd/xgbe/xgbe-ethtool.c
index 12395428ffe1..0bbb0decdae8 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-ethtool.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-ethtool.c
@@ -450,6 +450,7 @@ static int xgbe_get_coalesce(struct net_device *netdev,
 	ec->rx_coalesce_usecs = pdata->rx_usecs;
 	ec->rx_max_coalesced_frames = pdata->rx_frames;
 
+	ec->tx_coalesce_usecs = pdata->tx_usecs;
 	ec->tx_max_coalesced_frames = pdata->tx_frames;
 
 	return 0;
@@ -463,7 +464,8 @@ static int xgbe_set_coalesce(struct net_device *netdev,
 	struct xgbe_prv_data *pdata = netdev_priv(netdev);
 	struct xgbe_hw_if *hw_if = &pdata->hw_if;
 	unsigned int rx_frames, rx_riwt, rx_usecs;
-	unsigned int tx_frames;
+	unsigned int tx_frames, tx_usecs;
+	unsigned int jiffy_us = jiffies_to_usecs(1);
 
 	rx_riwt = hw_if->usec_to_riwt(pdata, ec->rx_coalesce_usecs);
 	rx_usecs = ec->rx_coalesce_usecs;
@@ -485,20 +487,42 @@ static int xgbe_set_coalesce(struct net_device *netdev,
 		return -EINVAL;
 	}
 
+	tx_usecs = ec->tx_coalesce_usecs;
 	tx_frames = ec->tx_max_coalesced_frames;
 
 	/* Check the bounds of values for Tx */
+	if (!tx_usecs) {
+		NL_SET_ERR_MSG_FMT_MOD(extack,
+				       "tx-usecs must not be 0");
+		return -EINVAL;
+	}
+	if (tx_usecs > XGMAC_MAX_COAL_TX_TICK) {
+		NL_SET_ERR_MSG_FMT_MOD(extack, "tx-usecs is limited to %d usec",
+				       XGMAC_MAX_COAL_TX_TICK);
+		return -EINVAL;
+	}
 	if (tx_frames > pdata->tx_desc_count) {
 		netdev_err(netdev, "tx-frames is limited to %d frames\n",
 			   pdata->tx_desc_count);
 		return -EINVAL;
 	}
 
+	/* Round tx-usecs to nearest multiple of jiffy granularity */
+	if (tx_usecs % jiffy_us) {
+		tx_usecs = rounddown(tx_usecs, jiffy_us);
+		if (!tx_usecs)
+			tx_usecs = jiffy_us;
+		NL_SET_ERR_MSG_FMT_MOD(extack,
+				       "tx-usecs rounded to %u usec due to jiffy granularity (%u usec)",
+				       tx_usecs, jiffy_us);
+	}
+
 	pdata->rx_riwt = rx_riwt;
 	pdata->rx_usecs = rx_usecs;
 	pdata->rx_frames = rx_frames;
 	hw_if->config_rx_coalesce(pdata);
 
+	pdata->tx_usecs = tx_usecs;
 	pdata->tx_frames = tx_frames;
 	hw_if->config_tx_coalesce(pdata);
 
@@ -830,7 +854,7 @@ static int xgbe_set_channels(struct net_device *netdev,
 }
 
 static const struct ethtool_ops xgbe_ethtool_ops = {
-	.supported_coalesce_params = ETHTOOL_COALESCE_RX_USECS |
+	.supported_coalesce_params = ETHTOOL_COALESCE_USECS |
 				     ETHTOOL_COALESCE_MAX_FRAMES,
 	.get_drvinfo = xgbe_get_drvinfo,
 	.get_msglevel = xgbe_get_msglevel,
diff --git a/drivers/net/ethernet/amd/xgbe/xgbe.h b/drivers/net/ethernet/amd/xgbe/xgbe.h
index 905959035a40..8f01f9a2be39 100755
--- a/drivers/net/ethernet/amd/xgbe/xgbe.h
+++ b/drivers/net/ethernet/amd/xgbe/xgbe.h
@@ -272,6 +272,7 @@
 /* Default coalescing parameters */
 #define XGMAC_INIT_DMA_TX_USECS		1000
 #define XGMAC_INIT_DMA_TX_FRAMES	25
+#define XGMAC_MAX_COAL_TX_TICK		100000
 
 #define XGMAC_MAX_DMA_RIWT		0xff
 #define XGMAC_INIT_DMA_RX_USECS		30
-- 
2.34.1