net: ethernet: stmmac: fix write to sgmii_adapter_base

I made a mistake with the commit a6aaa003 ("net: ethernet: stmmac:
fix altr_tse_pcs function when using a fixed-link"). I should have
tested against both scenario of having a SGMII interface and one
without.

Without the SGMII PCS TSE adpater, the sgmii_adapter_base address is
NULL, thus a write to this address will fail.

Cc: stable@vger.kernel.org
Fixes: a6aaa003 ("net: ethernet: stmmac: fix altr_tse_pcs function when using a fixed-link")
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lore.kernel.org/r/20220420152345.27415-1-dinguyen@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/dwmac-socfpga.c

@@ -65,8 +65,9 @@ static void socfpga_dwmac_fix_mac_speed(void *priv, unsigned int speed)
 	struct phy_device *phy_dev = ndev->phydev;
 	u32 val;
 
-	writew(SGMII_ADAPTER_DISABLE,
-	       sgmii_adapter_base + SGMII_ADAPTER_CTRL_REG);
+	if (sgmii_adapter_base)
+		writew(SGMII_ADAPTER_DISABLE,
+		       sgmii_adapter_base + SGMII_ADAPTER_CTRL_REG);
 
 	if (splitter_base) {
 		val = readl(splitter_base + EMAC_SPLITTER_CTRL_REG);
@@ -88,10 +89,11 @@ static void socfpga_dwmac_fix_mac_speed(void *priv, unsigned int speed)
 		writel(val, splitter_base + EMAC_SPLITTER_CTRL_REG);
 	}
 
-	writew(SGMII_ADAPTER_ENABLE,
-	       sgmii_adapter_base + SGMII_ADAPTER_CTRL_REG);
-	if (phy_dev)
+	if (phy_dev && sgmii_adapter_base) {
+		writew(SGMII_ADAPTER_ENABLE,
+		       sgmii_adapter_base + SGMII_ADAPTER_CTRL_REG);
 		tse_pcs_fix_mac_speed(&dwmac->pcs, phy_dev, speed);
+	}
 }
 
 static int socfpga_dwmac_parse_data(struct socfpga_dwmac *dwmac, struct device *dev)