nfp: centralize the buffer size calculation

Add a helper function to calculate the buffer size at run time.
Buffer lengths will now depend on the FW prepend configuration
instead of assuming the most space consuming configuration and
defaulting to 2k buffers at initialization time.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfp_net.h

@@ -75,7 +75,6 @@
 
 /* Default size for MTU and freelist buffer sizes */
 #define NFP_NET_DEFAULT_MTU		1500
-#define NFP_NET_DEFAULT_RX_BUFSZ	2048
 
 /* Maximum number of bytes prepended to a packet */
 #define NFP_NET_MAX_PREPEND		64

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -1030,6 +1030,19 @@ static void nfp_net_tx_timeout(struct net_device *netdev)
 
 /* Receive processing
  */
+static unsigned int
+nfp_net_calc_fl_bufsz(struct nfp_net *nn, unsigned int mtu)
+{
+	unsigned int fl_bufsz;
+
+	if (nn->rx_offset == NFP_NET_CFG_RX_OFFSET_DYNAMIC)
+		fl_bufsz = NFP_NET_MAX_PREPEND;
+	else
+		fl_bufsz = nn->rx_offset;
+	fl_bufsz += ETH_HLEN + VLAN_HLEN * 2 + mtu;
+
+	return fl_bufsz;
+}
 
 /**
  * nfp_net_rx_alloc_one() - Allocate and map skb for RX
@@ -2191,7 +2204,7 @@ static int nfp_net_change_mtu(struct net_device *netdev, int new_mtu)
 
 	old_mtu = netdev->mtu;
 	old_fl_bufsz = nn->fl_bufsz;
-	new_fl_bufsz = NFP_NET_MAX_PREPEND + ETH_HLEN + VLAN_HLEN * 2 + new_mtu;
+	new_fl_bufsz = nfp_net_calc_fl_bufsz(nn, new_mtu);
 
 	if (!netif_running(netdev)) {
 		netdev->mtu = new_mtu;
@@ -2731,12 +2744,18 @@ int nfp_net_netdev_init(struct net_device *netdev)
 
 	nfp_net_write_mac_addr(nn);
 
+	/* Determine RX packet/metadata boundary offset */
+	if (nn->fw_ver.major >= 2)
+		nn->rx_offset = nn_readl(nn, NFP_NET_CFG_RX_OFFSET);
+	else
+		nn->rx_offset = NFP_NET_RX_OFFSET;
+
 	/* Set default MTU and Freelist buffer size */
 	if (nn->max_mtu < NFP_NET_DEFAULT_MTU)
 		netdev->mtu = nn->max_mtu;
 	else
 		netdev->mtu = NFP_NET_DEFAULT_MTU;
-	nn->fl_bufsz = NFP_NET_DEFAULT_RX_BUFSZ;
+	nn->fl_bufsz = nfp_net_calc_fl_bufsz(nn, netdev->mtu);
 
 	/* Advertise/enable offloads based on capabilities
 	 *
@@ -2807,12 +2826,6 @@ int nfp_net_netdev_init(struct net_device *netdev)
 		nn->ctrl |= NFP_NET_CFG_CTRL_IRQMOD;
 	}
 
-	/* Determine RX packet/metadata boundary offset */
-	if (nn->fw_ver.major >= 2)
-		nn->rx_offset = nn_readl(nn, NFP_NET_CFG_RX_OFFSET);
-	else
-		nn->rx_offset = NFP_NET_RX_OFFSET;
-
 	/* Stash the re-configuration queue away.  First odd queue in TX Bar */
 	nn->qcp_cfg = nn->tx_bar + NFP_QCP_QUEUE_ADDR_SZ;