net: airoha: Fix PPE table access in airoha_ppe_debugfs_foe_show()

In order to avoid any possible race we need to hold the ppe_lock
spinlock accessing the hw PPE table. airoha_ppe_foe_get_entry routine is
always executed holding ppe_lock except in airoha_ppe_debugfs_foe_show
routine. Fix the problem introducing airoha_ppe_foe_get_entry_locked
routine.

Fixes: 3fe15c6 ("net: airoha: Introduce PPE debugfs support")
Reviewed-by: Dawid Osuchowski <[email protected]>
Signed-off-by: Lorenzo Bianconi <[email protected]>
Link: https://patch.msgid.link/20250731-airoha_ppe_foe_get_entry_locked-v2-1-50efbd8c0fd6@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>

Author: LorenzoBianconi

drivers/net/ethernet/airoha/airoha_ppe.c

@@ -508,9 +508,11 @@ static void airoha_ppe_foe_flow_stats_update(struct airoha_ppe *ppe,
 		FIELD_PREP(AIROHA_FOE_IB2_NBQ, nbq);
 }
 
-struct airoha_foe_entry *airoha_ppe_foe_get_entry(struct airoha_ppe *ppe,
-						  u32 hash)
+static struct airoha_foe_entry *
+airoha_ppe_foe_get_entry_locked(struct airoha_ppe *ppe, u32 hash)
 {
+	lockdep_assert_held(&ppe_lock);
+
 	if (hash < PPE_SRAM_NUM_ENTRIES) {
 		u32 *hwe = ppe->foe + hash * sizeof(struct airoha_foe_entry);
 		struct airoha_eth *eth = ppe->eth;
@@ -537,6 +539,18 @@ struct airoha_foe_entry *airoha_ppe_foe_get_entry(struct airoha_ppe *ppe,
 	return ppe->foe + hash * sizeof(struct airoha_foe_entry);
 }
 
+struct airoha_foe_entry *airoha_ppe_foe_get_entry(struct airoha_ppe *ppe,
+						  u32 hash)
+{
+	struct airoha_foe_entry *hwe;
+
+	spin_lock_bh(&ppe_lock);
+	hwe = airoha_ppe_foe_get_entry_locked(ppe, hash);
+	spin_unlock_bh(&ppe_lock);
+
+	return hwe;
+}
+
 static bool airoha_ppe_foe_compare_entry(struct airoha_flow_table_entry *e,
 					 struct airoha_foe_entry *hwe)
 {
@@ -651,7 +665,7 @@ airoha_ppe_foe_commit_subflow_entry(struct airoha_ppe *ppe,
 	struct airoha_flow_table_entry *f;
 	int type;
 
-	hwe_p = airoha_ppe_foe_get_entry(ppe, hash);
+	hwe_p = airoha_ppe_foe_get_entry_locked(ppe, hash);
 	if (!hwe_p)
 		return -EINVAL;
 
@@ -703,7 +717,7 @@ static void airoha_ppe_foe_insert_entry(struct airoha_ppe *ppe,
 
 	spin_lock_bh(&ppe_lock);
 
-	hwe = airoha_ppe_foe_get_entry(ppe, hash);
+	hwe = airoha_ppe_foe_get_entry_locked(ppe, hash);
 	if (!hwe)
 		goto unlock;
 
@@ -818,7 +832,7 @@ airoha_ppe_foe_flow_l2_entry_update(struct airoha_ppe *ppe,
 		u32 ib1, state;
 		int idle;
 
-		hwe = airoha_ppe_foe_get_entry(ppe, iter->hash);
+		hwe = airoha_ppe_foe_get_entry_locked(ppe, iter->hash);
 		if (!hwe)
 			continue;
 
@@ -855,7 +869,7 @@ static void airoha_ppe_foe_flow_entry_update(struct airoha_ppe *ppe,
 	if (e->hash == 0xffff)
 		goto unlock;
 
-	hwe_p = airoha_ppe_foe_get_entry(ppe, e->hash);
+	hwe_p = airoha_ppe_foe_get_entry_locked(ppe, e->hash);
 	if (!hwe_p)
 		goto unlock;