kernel: vrx518_tc: fix ADSL/ATM operation

ATM TC layer have some issues which effectively prevent VRX518 from
being used as ADSL modem. Specifically, there one crash during the ATM
layer configuration and wrong PVC ID selection on packet receiving what
breaks RX path. Fix both of the issues. Make subif iface registration
optional to prevent the crash (see more details in the new patch) and
update the hardcoded PVC ID to match the first allocated channel.

Run tested with FRITZ!Box 7530.

Fixes: 474bbe23 ("kernel: add Intel/Lantiq VRX518 TC driver")
Reported-and-tested-by:  <nebibigon93@yandex.ru>
Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
Link: https://patchwork.ozlabs.org/project/openwrt/patch/20250122222654.21833-3-ryazanov.s.a@gmail.com/


Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit 47033545)

package/kernel/lantiq/vrx518_tc/patches/100-compat.patch

@@ -166,7 +166,7 @@
  
 -	return (skb->DW0 >> 3) & 0xF;
 +// 	return (skb->DW0 >> 3) & 0xF;
-+	return 1;
++	return 0;	/* We use only one connection for now, so return the first connection id */
  }
  
  static int atm_get_qid_by_vcc(struct net_device *dev, struct sk_buff *skb,

package/kernel/lantiq/vrx518_tc/patches/207-dcdp-atm_tc-fix-crash-on-subif_reg-absence.patch

+From: Sergey Ryazanov <ryazanov.s.a@gmail.com>
+Date: Fri, 10 Jan 2025 00:57:27 +0000
+Subject: [PATCH] vrx518_tc: atm_tc: fix crash on subif_reg absence
+
+VRX518 (sw_plat) platform does not provid the subif_reg/subif_unreg ops
+in the same time ATM TC layer unconditionally calls them, what leads to
+the kernel crash on the atm_hook_mpoa_setup hook invocation from the ATM
+stack:
+
+  vrx518_tc:mpoa_setup_sync : sync: conn: 0, vpi: 0, vci: 35, mpoa_type: 0, mpoa_mode: 0
+  Unable to handle kernel NULL pointer dereference at virtual address 00000000
+
+Subif registration is optional and PTM TC do this only when the
+corresponding ops are defined. Do the same for ATM TC and call
+subif_reg/subif_unreg only if they are not NULL.
+
+While at it, move subif related data preparation under the 'if' block
+in order to group and isolate that aux code.
+
+Run tested with FRITZ!Box 7530.
+
+Signed-off-by: Sergey Ryazanov <ryazanov.s.a@gmail.com>
+---
+--- a/dcdp/atm_tc.c
++++ b/dcdp/atm_tc.c
+@@ -1232,8 +1232,9 @@ static void ppe_close(struct atm_vcc *vc
+ 		validate_oam_htu_entry(priv, 0);
+ 	spin_unlock_bh(&priv->atm_lock);
+ 
+-	priv->tc_priv->tc_ops.subif_unreg(dev, (!dev) ? dev_name : dev->name,
+-					priv->conn[cid].subif_id, 0);
++	if (priv->tc_priv->tc_ops.subif_unreg)
++		priv->tc_priv->tc_ops.subif_unreg(dev, (!dev) ? dev_name : dev->name,
++						  priv->conn[cid].subif_id, 0);
+ 				
+ 	memset(conn, 0, sizeof(*conn));
+ 
+@@ -2791,24 +2792,26 @@ static void mpoa_setup_sync(struct atm_p
+ 	struct wtx_queue_config_t tx_qcfg;
+ 	struct uni_cell_header *cell_header;
+ 	struct atm_vcc *vcc;
+-	struct net_device *dev;
+-	char dev_name[32];
+ 
+ 	tc_dbg(priv->tc_priv, MSG_INIT,
+ 		"sync: conn: %d, vpi: %d, vci: %d, mpoa_type: %d, mpoa_mode: %d\n",
+ 		conn, priv->conn[conn].vcc->vpi, priv->conn[conn].vcc->vci,
+ 		priv->conn[conn].mpoa_type, priv->conn[conn].mpoa_mode);
+ 
+-	dev = priv->conn[conn].dev;
++	if (priv->tc_priv->tc_ops.subif_reg) {
++		struct net_device *dev;
++		char dev_name[32];
++
++		dev = priv->conn[conn].dev;
++		if (!dev)
++			sprintf(dev_name, "atm_%d%d",
++				priv->conn[conn].vcc->vpi, priv->conn[conn].vcc->vci);
+ 
+-	if (!dev)
+-		sprintf(dev_name, "atm_%d%d",
+-			priv->conn[conn].vcc->vpi, priv->conn[conn].vcc->vci);
+-
+-	priv->tc_priv->tc_ops.subif_reg(dev, (!dev) ? dev_name : dev->name,
+-				&priv->conn[conn].subif_id, 0);
+-	tc_dbg(priv->tc_priv, MSG_INIT,
+-		"conn[%d]subif_id[%x]", conn, priv->conn[conn].subif_id);
++		priv->tc_priv->tc_ops.subif_reg(dev, !dev ? dev_name : dev->name,
++						&priv->conn[conn].subif_id, 0);
++		tc_dbg(priv->tc_priv, MSG_INIT,
++		       "conn[%d]subif_id[%x]", conn, priv->conn[conn].subif_id);
++	}
+ 	vcc = priv->conn[conn].vcc;
+ 
+ 	/*  set htu entry   */