net: stmmac: Balance PTP reference clock enable/disable

clk_prepare_enable() and clk_disable_unprepare() for this clock aren't
properly balanced, which can trigger a WARN_ON() in the common clock
framework.
Reviewed-By: Joao Pinto <jpinto@synopsys.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -1711,6 +1711,10 @@ static int stmmac_hw_setup(struct net_device *dev, bool init_ptp)
 	stmmac_mmc_setup(priv);
 
 	if (init_ptp) {
+		ret = clk_prepare_enable(priv->plat->clk_ptp_ref);
+		if (ret < 0)
+			netdev_warn(priv->dev, "failed to enable PTP reference clock: %d\n", ret);
+
 		ret = stmmac_init_ptp(priv);
 		if (ret == -EOPNOTSUPP)
 			netdev_warn(priv->dev, "PTP not supported by HW\n");

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

@@ -365,7 +365,6 @@ stmmac_probe_config_dt(struct platform_device *pdev, const char **mac)
 		plat->clk_ptp_ref = NULL;
 		dev_warn(&pdev->dev, "PTP uses main clock\n");
 	} else {
-		clk_prepare_enable(plat->clk_ptp_ref);
 		plat->clk_ptp_rate = clk_get_rate(plat->clk_ptp_ref);
 		dev_dbg(&pdev->dev, "PTP rate %d\n", plat->clk_ptp_rate);
 	}