net: stmmac: make SPH enable/disable to be configurable

SPH functionality splits header and payload according to split mode and
offsef fields (SPLM and SPLOFST). It is beneficials for Linux network
stack RX processing however it adds a lot of complexity in XDP
processing.

So, this patch makes the split-header (SPH) capability of the controller
is stored in "priv->sph_cap" and the enabling/disabling of SPH is decided
by "priv->sph".

This is to prepare initial XDP enabling for stmmac to disable the use of
SPH whenever XDP is enabled.
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -160,6 +160,7 @@ struct stmmac_priv {
 	bool tx_path_in_lpi_mode;
 	bool tso;
 	int sph;
+	int sph_cap;
 	u32 sarc_type;
 
 	unsigned int dma_buf_sz;

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -2858,6 +2858,7 @@ static int stmmac_hw_setup(struct net_device *dev, bool init_ptp)
 	struct stmmac_priv *priv = netdev_priv(dev);
 	u32 rx_cnt = priv->plat->rx_queues_to_use;
 	u32 tx_cnt = priv->plat->tx_queues_to_use;
+	bool sph_en;
 	u32 chan;
 	int ret;
 
@@ -2952,10 +2953,10 @@ static int stmmac_hw_setup(struct net_device *dev, bool init_ptp)
 	}
 
 	/* Enable Split Header */
-	if (priv->sph && priv->hw->rx_csum) {
+	sph_en = (priv->hw->rx_csum > 0) && priv->sph;
 	for (chan = 0; chan < rx_cnt; chan++)
-			stmmac_enable_sph(priv, priv->ioaddr, 1, chan);
-	}
+		stmmac_enable_sph(priv, priv->ioaddr, sph_en, chan);
+
 
 	/* VLAN Tag Insertion */
 	if (priv->dma_cap.vlins)
@@ -5708,7 +5709,8 @@ int stmmac_dvr_probe(struct device *device,
 
 	if (priv->dma_cap.sphen) {
 		ndev->hw_features |= NETIF_F_GRO;
-		priv->sph = true;
+		priv->sph_cap = true;
+		priv->sph = priv->sph_cap;
 		dev_info(priv->device, "SPH feature enabled\n");
 	}