can: mcp251xfd: mcp251xfd_ring_init(): check TX-coalescing configuration

When changing the interface from CAN-CC to CAN-FD mode the old
coalescing parameters are re-used. This might cause problem, as the
configured parameters are too big for CAN-FD mode.

During testing an invalid TX coalescing configuration has been seen.
The problem should be been fixed in the previous patch, but add a
safeguard here to ensure that the number of TEF coalescing buffers (if
configured) is exactly the half of all TEF buffers.

Link: https://lore.kernel.org/all/20240805-mcp251xfd-fix-ringconfig-v1-2-72086f0ca5ee@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-ring.c

@@ -290,7 +290,7 @@ int mcp251xfd_ring_init(struct mcp251xfd_priv *priv)
 	const struct mcp251xfd_rx_ring *rx_ring;
 	u16 base = 0, ram_used;
 	u8 fifo_nr = 1;
-	int i;
+	int err = 0, i;
 
 	netdev_reset_queue(priv->ndev);
 
@@ -386,10 +386,18 @@ int mcp251xfd_ring_init(struct mcp251xfd_priv *priv)
 		netdev_err(priv->ndev,
 			   "Error during ring configuration, using more RAM (%u bytes) than available (%u bytes).\n",
 			   ram_used, MCP251XFD_RAM_SIZE);
-		return -ENOMEM;
+		err = -ENOMEM;
 	}
 
-	return 0;
+	if (priv->tx_obj_num_coalesce_irq &&
+	    priv->tx_obj_num_coalesce_irq * 2 != priv->tx->obj_num) {
+		netdev_err(priv->ndev,
+			   "Error during ring configuration, number of TEF coalescing buffers (%u) must be half of TEF buffers (%u).\n",
+			   priv->tx_obj_num_coalesce_irq, priv->tx->obj_num);
+		err = -EINVAL;
+	}
+
+	return err;
 }
 
 void mcp251xfd_ring_free(struct mcp251xfd_priv *priv)