can: mcp251xfd: fix ring configuration when switching from CAN-CC to CAN-FD mode

If the ring (rx, tx) and/or coalescing parameters (rx-frames-irq,
tx-frames-irq) have been configured while the interface was in CAN-CC
mode, but the interface is brought up in CAN-FD mode, the ring
parameters might be too big.

Use the default CAN-FD values in this case.

Fixes: 9263c2e9 ("can: mcp251xfd: ring: add support for runtime configurable RX/TX ring parameters")
Link: https://lore.kernel.org/all/20240805-mcp251xfd-fix-ringconfig-v1-1-72086f0ca5ee@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

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

@@ -97,7 +97,16 @@ void can_ram_get_layout(struct can_ram_layout *layout,
 	if (ring) {
 		u8 num_rx_coalesce = 0, num_tx_coalesce = 0;
 
-		num_rx = can_ram_rounddown_pow_of_two(config, &config->rx, 0, ring->rx_pending);
+		/* If the ring parameters have been configured in
+		 * CAN-CC mode, but and we are in CAN-FD mode now,
+		 * they might be to big. Use the default CAN-FD values
+		 * in this case.
+		 */
+		num_rx = ring->rx_pending;
+		if (num_rx > layout->max_rx)
+			num_rx = layout->default_rx;
+
+		num_rx = can_ram_rounddown_pow_of_two(config, &config->rx, 0, num_rx);
 
 		/* The ethtool doc says:
 		 * To disable coalescing, set usecs = 0 and max_frames = 1.

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

@@ -469,11 +469,25 @@ int mcp251xfd_ring_alloc(struct mcp251xfd_priv *priv)
 
 	/* switching from CAN-2.0 to CAN-FD mode or vice versa */
 	if (fd_mode != test_bit(MCP251XFD_FLAGS_FD_MODE, priv->flags)) {
+		const struct ethtool_ringparam ring = {
+			.rx_pending = priv->rx_obj_num,
+			.tx_pending = priv->tx->obj_num,
+		};
+		const struct ethtool_coalesce ec = {
+			.rx_coalesce_usecs_irq = priv->rx_coalesce_usecs_irq,
+			.rx_max_coalesced_frames_irq = priv->rx_obj_num_coalesce_irq,
+			.tx_coalesce_usecs_irq = priv->tx_coalesce_usecs_irq,
+			.tx_max_coalesced_frames_irq = priv->tx_obj_num_coalesce_irq,
+		};
 		struct can_ram_layout layout;
 
-		can_ram_get_layout(&layout, &mcp251xfd_ram_config, NULL, NULL, fd_mode);
-		priv->rx_obj_num = layout.default_rx;
-		tx_ring->obj_num = layout.default_tx;
+		can_ram_get_layout(&layout, &mcp251xfd_ram_config, &ring, &ec, fd_mode);
+
+		priv->rx_obj_num = layout.cur_rx;
+		priv->rx_obj_num_coalesce_irq = layout.rx_coalesce;
+
+		tx_ring->obj_num = layout.cur_tx;
+		priv->tx_obj_num_coalesce_irq = layout.tx_coalesce;
 	}
 
 	if (fd_mode) {