phy: lynx-28g: serialize concurrent phy_set_mode_ext() calls to shared registers

The protocol converter configuration registers PCC8, PCCC, PCCD
(implemented by the driver), as well as others, control protocol
converters from multiple lanes (each represented as a different
struct phy). So, if there are simultaneous calls to phy_set_mode_ext()
to lanes sharing the same PCC register (either for the "old" or for the
"new" protocol), corruption of the values programmed to hardware is
possible, because lynx_28g_rmw() has no locking.

Add a spinlock in the struct lynx_28g_priv shared by all lanes, and take
the global spinlock from the phy_ops :: set_mode() implementation. There
are no other callers which modify PCC registers.

Fixes: 8f73b37 ("phy: add support for the Layerscape SerDes 28G")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: vladimiroltean

drivers/phy/freescale/phy-fsl-lynx-28g.c

@@ -127,6 +127,10 @@ struct lynx_28g_lane {
 struct lynx_28g_priv {
 	void __iomem *base;
 	struct device *dev;
+	/* Serialize concurrent access to registers shared between lanes,
+	 * like PCCn
+	 */
+	spinlock_t pcc_lock;
 	struct lynx_28g_pll pll[LYNX_28G_NUM_PLL];
 	struct lynx_28g_lane lane[LYNX_28G_NUM_LANE];
 
@@ -397,6 +401,8 @@ static int lynx_28g_set_mode(struct phy *phy, enum phy_mode mode, int submode)
 	if (powered_up)
 		lynx_28g_power_off(phy);
 
+	spin_lock(&priv->pcc_lock);
+
 	switch (submode) {
 	case PHY_INTERFACE_MODE_SGMII:
 	case PHY_INTERFACE_MODE_1000BASEX:
@@ -413,6 +419,8 @@ static int lynx_28g_set_mode(struct phy *phy, enum phy_mode mode, int submode)
 	lane->interface = submode;
 
 out:
+	spin_unlock(&priv->pcc_lock);
+
 	/* Power up the lane if necessary */
 	if (powered_up)
 		lynx_28g_power_on(phy);
@@ -596,6 +604,7 @@ static int lynx_28g_probe(struct platform_device *pdev)
 
 	dev_set_drvdata(dev, priv);
 
+	spin_lock_init(&priv->pcc_lock);
 	INIT_DELAYED_WORK(&priv->cdr_check, lynx_28g_cdr_lock_check);
 
 	queue_delayed_work(system_power_efficient_wq, &priv->cdr_check,