[PATCH iwl-next v4] ixgbe: preserve RSS indirection table across admin down/up

[Kohei Enju <enjuk@amazon.com>]

Currently, the RSS indirection table configured by user via ethtool is
reinitialized to default values during interface resets (e.g., admin
down/up, MTU change). As for RSS hash key, commit 3dfbfc7ebb95 ("ixgbe:
Check for RSS key before setting value") made it persistent across
interface resets.

Adopt the same approach used in igc and igb drivers which reinitializes
the RSS indirection table only when the queue count changes. Since the
number of RETA entries can also change in ixgbe, let's make user
configuration persistent as long as both queue count and the number of
RETA entries remain unchanged.

Tested on Intel Corporation 82599ES 10-Gigabit SFI/SFP+ Network
Connection.

Test:
Set custom indirection table and check the value after interface down/up

  # ethtool --set-rxfh-indir ens5 equal 2
  # ethtool --show-rxfh-indir ens5 | head -5

  RX flow hash indirection table for ens5 with 12 RX ring(s):
      0:      0     1     0     1     0     1     0     1
      8:      0     1     0     1     0     1     0     1
     16:      0     1     0     1     0     1     0     1
  # ip link set dev ens5 down && ip link set dev ens5 up

Without patch:
  # ethtool --show-rxfh-indir ens5 | head -5

  RX flow hash indirection table for ens5 with 12 RX ring(s):
      0:      0     1     2     3     4     5     6     7
      8:      8     9    10    11     0     1     2     3
     16:      4     5     6     7     8     9    10    11

With patch:
  # ethtool --show-rxfh-indir ens5 | head -5

  RX flow hash indirection table for ens5 with 12 RX ring(s):
      0:      0     1     0     1     0     1     0     1
      8:      0     1     0     1     0     1     0     1
     16:      0     1     0     1     0     1     0     1

Signed-off-by: Kohei Enju <enjuk@amazon.com>
---
Changes:
v3->v4:
  - ensure rss_i is non-zero to avoid zero-division
v2->v3: https://lore.kernel.org/intel-wired-lan/20250902121203.12454-1-enjuk@amazon.com/
  - s/last_rss_i/last_rss_indices/ for clarity
  - use modulo instead of top-of-loop equality test
  - use ixgbe_rss_indir_tbl_entries() instead of magic number
v1->v2: https://lore.kernel.org/intel-wired-lan/20250828160134.81286-1-enjuk@amazon.com/
  - remove pointless memset() in  ixgbe_setup_reta()
  - add check for reta_entries in addition to rss_i
  - update the commit message to reflect the additional check
v1: https://lore.kernel.org/intel-wired-lan/20250824112037.32692-1-enjuk@amazon.com/
---
 drivers/net/ethernet/intel/ixgbe/ixgbe.h      |  2 +
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 45 +++++++++++++------
 2 files changed, 33 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index 14d275270123..3553bf659d42 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -838,6 +838,8 @@ struct ixgbe_adapter {
  */
 #define IXGBE_MAX_RETA_ENTRIES 512
 	u8 rss_indir_tbl[IXGBE_MAX_RETA_ENTRIES];
+	u32 last_reta_entries;
+	u16 last_rss_indices;
 
 #define IXGBE_RSS_KEY_SIZE     40  /* size of RSS Hash Key in bytes */
 	u32 *rss_key;
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 3190ce7e44c7..90d1979e3c36 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -4309,9 +4309,9 @@ static void ixgbe_store_vfreta(struct ixgbe_adapter *adapter)
 
 static void ixgbe_setup_reta(struct ixgbe_adapter *adapter)
 {
-	u32 i, j;
 	u32 reta_entries = ixgbe_rss_indir_tbl_entries(adapter);
 	u16 rss_i = adapter->ring_feature[RING_F_RSS].indices;
+	u32 i;
 
 	/* Program table for at least 4 queues w/ SR-IOV so that VFs can
 	 * make full use of any rings they may have.  We will use the
@@ -4323,14 +4323,21 @@ static void ixgbe_setup_reta(struct ixgbe_adapter *adapter)
 	/* Fill out hash function seeds */
 	ixgbe_store_key(adapter);
 
-	/* Fill out redirection table */
-	memset(adapter->rss_indir_tbl, 0, sizeof(adapter->rss_indir_tbl));
+	/* Ensure rss_i is non-zero to avoid division by zero */
+	if (!rss_i)
+		rss_i = 1;
 
-	for (i = 0, j = 0; i < reta_entries; i++, j++) {
-		if (j == rss_i)
-			j = 0;
+	/* Update redirection table in memory on first init, queue count change,
+	 * or reta entries change, otherwise preserve user configurations. Then
+	 * always write to hardware.
+	 */
+	if (adapter->last_rss_indices != rss_i ||
+	    adapter->last_reta_entries != reta_entries) {
+		for (i = 0; i < reta_entries; i++)
+			adapter->rss_indir_tbl[i] = i % rss_i;
 
-		adapter->rss_indir_tbl[i] = j;
+		adapter->last_rss_indices = rss_i;
+		adapter->last_reta_entries = reta_entries;
 	}
 
 	ixgbe_store_reta(adapter);
@@ -4338,9 +4345,10 @@ static void ixgbe_setup_reta(struct ixgbe_adapter *adapter)
 
 static void ixgbe_setup_vfreta(struct ixgbe_adapter *adapter)
 {
-	struct ixgbe_hw *hw = &adapter->hw;
+	u32 reta_entries = ixgbe_rss_indir_tbl_entries(adapter);
 	u16 rss_i = adapter->ring_feature[RING_F_RSS].indices;
-	int i, j;
+	struct ixgbe_hw *hw = &adapter->hw;
+	int i;
 
 	/* Fill out hash function seeds */
 	for (i = 0; i < 10; i++) {
@@ -4352,12 +4360,21 @@ static void ixgbe_setup_vfreta(struct ixgbe_adapter *adapter)
 					*(adapter->rss_key + i));
 	}
 
-	/* Fill out the redirection table */
-	for (i = 0, j = 0; i < 64; i++, j++) {
-		if (j == rss_i)
-			j = 0;
+	/* Ensure rss_i is non-zero to avoid division by zero */
+	if (!rss_i)
+		rss_i = 1;
+
+	/* Update redirection table in memory on first init, queue count change,
+	 * or reta entries change, otherwise preserve user configurations. Then
+	 * always write to hardware.
+	 */
+	if (adapter->last_rss_indices != rss_i ||
+	    adapter->last_reta_entries != reta_entries) {
+		for (i = 0; i < reta_entries; i++)
+			adapter->rss_indir_tbl[i] = i % rss_i;
 
-		adapter->rss_indir_tbl[i] = j;
+		adapter->last_rss_indices = rss_i;
+		adapter->last_reta_entries = reta_entries;
 	}
 
 	ixgbe_store_vfreta(adapter);
-- 
2.51.0