stmmac: hardware TX COE doesn't work when force_thresh_dma_mode is set

Clear the TX COE bit when force_thresh_dma_mode is set even hardware
dma capability says support.

Tested on BF609.
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -2755,7 +2755,11 @@ static int stmmac_hw_init(struct stmmac_priv *priv)
 		priv->plat->enh_desc = priv->dma_cap.enh_desc;
 		priv->plat->pmt = priv->dma_cap.pmt_remote_wake_up;
 
-		priv->plat->tx_coe = priv->dma_cap.tx_coe;
+		/* TXCOE doesn't work in thresh DMA mode */
+		if (priv->plat->force_thresh_dma_mode)
+			priv->plat->tx_coe = 0;
+		else
+			priv->plat->tx_coe = priv->dma_cap.tx_coe;
 
 		if (priv->dma_cap.rx_coe_type2)
 			priv->plat->rx_coe = STMMAC_RX_COE_TYPE2;