[PATCH net-next v3 4/4] amd-xgbe: add RSS ethtool self-test

[Raju Rangoju <Raju.Rangoju@amd.com>]

Add a Receive Side Scaling (RSS) self-test to the ethtool diagnostic
suite to verify that the hardware correctly computes hash values for
incoming packets.

The test validates RSS functionality by:
1. Checking for RSS hardware feature support (rss bit in MAC_HWF1R)
2. Sending a test packet with specific TCP/UDP ports to trigger
   hash computation
3. Verifying that the received packet has a non-zero hash value
   computed by the hardware

The test uses the existing loopback infrastructure and requires
PHY loopback mode. It uses specific port values (sport=0xabc,
dport=0xdef) to generate a deterministic hash that exercises
the RSS hash computation logic.

This test helps users verify that RSS is properly configured and
functioning, which is essential for multi-queue performance on
multi-core systems.

Usage:
  $ ethtool -t <interface>

Signed-off-by: Raju Rangoju <Raju.Rangoju@amd.com>
---
 drivers/net/ethernet/amd/xgbe/xgbe-selftest.c | 32 +++++++++++++++++++
 include/net/selftests.h                       |  1 +
 2 files changed, 33 insertions(+)

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-selftest.c b/drivers/net/ethernet/amd/xgbe/xgbe-selftest.c
index 6cb73ff7cf37..296c45d2bb3c 100644
--- a/drivers/net/ethernet/amd/xgbe/xgbe-selftest.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-selftest.c
@@ -214,8 +214,13 @@ static int xgbe_test_loopback_validate(struct sk_buff *skb,
 	if (tdata->packet->id != hdr->id)
 		goto out;
 
+	/* Validate RSS hash if expected */
+	if (tdata->packet->exp_hash && !skb->hash)
+		goto out;
+
 	tdata->ok = true;
 	complete(&tdata->comp);
+
 out:
 	kfree_skb(skb);
 	return 0;
@@ -268,6 +273,29 @@ static int __xgbe_test_loopback(struct xgbe_prv_data *pdata,
 	return ret;
 }
 
+static int xgbe_test_rss(struct xgbe_prv_data *pdata)
+{
+	struct net_packet_attrs attr = {};
+	int ret;
+
+	/* Check for RSS hardware support */
+	if (!pdata->hw_feat.rss)
+		return -EOPNOTSUPP;
+
+	attr.dst = pdata->netdev->dev_addr;
+	/*
+	 * Use specific port values to generate a hash.
+	 * The asymmetric port values ensure the hash computation
+	 * produces a non-zero result for test validation.
+	 */
+	attr.sport = 0xabc;
+	attr.dport = 0xdef;
+	attr.exp_hash = true;
+	ret = __xgbe_test_loopback(pdata, &attr);
+
+	return ret;
+}
+
 static int xgbe_test_mac_loopback(struct xgbe_prv_data *pdata)
 {
 	struct net_packet_attrs attr = {};
@@ -371,6 +399,10 @@ static const struct xgbe_test xgbe_selftests[] = {
 		.name = "ARP Offload    ",
 		.lb = XGBE_LOOPBACK_PHY,
 		.fn = xgbe_test_arpoffload,
+	}, {
+		.name = "RSS           ",
+		.lb = XGBE_LOOPBACK_PHY,
+		.fn = xgbe_test_rss,
 	}
 };
 
diff --git a/include/net/selftests.h b/include/net/selftests.h
index c36e07406ad4..18a9b4830dfc 100644
--- a/include/net/selftests.h
+++ b/include/net/selftests.h
@@ -19,6 +19,7 @@ struct net_packet_attrs {
 	u8 id;
 	u16 queue_mapping;
 	bool bad_csum;
+	u32 exp_hash;
 };
 
 struct net_test_priv {
-- 
2.34.1