stmmac: Allow SOCs to use Store forward mode eventhough tx_coe is 0. (V2)

This patch adds new field 'force_sf_dma_mode' to plat_stmmacenet_data
struct to allow users to specify if they want to use force store forward
eventhough tx_coe is not available in hw.
without this flag stmmac driver will use cut-thru mode not use
store-forward mode.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/stmmac/stmmac_main.c

@@ -557,9 +557,11 @@ static void free_dma_desc_resources(struct stmmac_priv *priv)
  */
 static void stmmac_dma_operation_mode(struct stmmac_priv *priv)
 {
-	if (likely((priv->plat->tx_coe) && (!priv->no_csum_insertion))) {
-		/* In case of GMAC, SF mode has to be enabled
-		 * to perform the TX COE. This depends on:
+	if (likely(priv->plat->force_sf_dma_mode ||
+		((priv->plat->tx_coe) && (!priv->no_csum_insertion)))) {
+		/*
+		 * In case of GMAC, SF mode can be enabled
+		 * to perform the TX COE in HW. This depends on:
 		 * 1) TX COE if actually supported
 		 * 2) There is no bugged Jumbo frame support
 		 *    that needs to not insert csum in the TDES.

include/linux/stmmac.h

@@ -40,6 +40,7 @@ struct plat_stmmacenet_data {
 	int tx_coe;
 	int bugged_jumbo;
 	int pmt;
+	int force_sf_dma_mode;
 	void (*fix_mac_speed)(void *priv, unsigned int speed);
 	void (*bus_setup)(void __iomem *ioaddr);
 	int (*init)(struct platform_device *pdev);