net: fec: Use a spinlock to guard `fep->ptp_clk_on`

Mutexes cannot be taken in a non-preemptible context,
causing a panic in `fec_ptp_save_state()`. Replacing
`ptp_clk_mutex` by `tmreg_lock` fixes this.

Fixes: 6a4d7234 ("net: fec: ptp: avoid register access when ipg clock is disabled")
Fixes: f7995922 ("fec: Restart PPS after link state change")
Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/all/20220827160922.642zlcd5foopozru@pengutronix.de/Signed-off-by: Csókás Bence <csokas.bence@prolan.hu>
Tested-by: Francesco Dolcini <francesco.dolcini@toradex.com> # Toradex Apalis iMX6
Link: https://lore.kernel.org/r/20220901140402.64804-1-csokas.bence@prolan.huSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/fec.h

@@ -561,7 +561,6 @@ struct fec_enet_private {
 	struct clk *clk_2x_txclk;
 
 	bool ptp_clk_on;
-	struct mutex ptp_clk_mutex;
 	unsigned int num_tx_queues;
 	unsigned int num_rx_queues;
 

drivers/net/ethernet/freescale/fec_main.c

@@ -2029,6 +2029,7 @@ static void fec_enet_phy_reset_after_clk_enable(struct net_device *ndev)
 static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
 {
 	struct fec_enet_private *fep = netdev_priv(ndev);
+	unsigned long flags;
 	int ret;
 
 	if (enable) {
@@ -2037,15 +2038,15 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
 			return ret;
 
 		if (fep->clk_ptp) {
-			mutex_lock(&fep->ptp_clk_mutex);
+			spin_lock_irqsave(&fep->tmreg_lock, flags);
 			ret = clk_prepare_enable(fep->clk_ptp);
 			if (ret) {
-				mutex_unlock(&fep->ptp_clk_mutex);
+				spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 				goto failed_clk_ptp;
 			} else {
 				fep->ptp_clk_on = true;
 			}
-			mutex_unlock(&fep->ptp_clk_mutex);
+			spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 		}
 
 		ret = clk_prepare_enable(fep->clk_ref);
@@ -2060,10 +2061,10 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
 	} else {
 		clk_disable_unprepare(fep->clk_enet_out);
 		if (fep->clk_ptp) {
-			mutex_lock(&fep->ptp_clk_mutex);
+			spin_lock_irqsave(&fep->tmreg_lock, flags);
 			clk_disable_unprepare(fep->clk_ptp);
 			fep->ptp_clk_on = false;
-			mutex_unlock(&fep->ptp_clk_mutex);
+			spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 		}
 		clk_disable_unprepare(fep->clk_ref);
 		clk_disable_unprepare(fep->clk_2x_txclk);
@@ -2076,10 +2077,10 @@ static int fec_enet_clk_enable(struct net_device *ndev, bool enable)
 		clk_disable_unprepare(fep->clk_ref);
 failed_clk_ref:
 	if (fep->clk_ptp) {
-		mutex_lock(&fep->ptp_clk_mutex);
+		spin_lock_irqsave(&fep->tmreg_lock, flags);
 		clk_disable_unprepare(fep->clk_ptp);
 		fep->ptp_clk_on = false;
-		mutex_unlock(&fep->ptp_clk_mutex);
+		spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 	}
 failed_clk_ptp:
 	clk_disable_unprepare(fep->clk_enet_out);
@@ -3914,7 +3915,7 @@ fec_probe(struct platform_device *pdev)
 	}
 
 	fep->ptp_clk_on = false;
-	mutex_init(&fep->ptp_clk_mutex);
+	spin_lock_init(&fep->tmreg_lock);
 
 	/* clk_ref is optional, depends on board */
 	fep->clk_ref = devm_clk_get_optional(&pdev->dev, "enet_clk_ref");

drivers/net/ethernet/freescale/fec_ptp.c

@@ -365,21 +365,19 @@ static int fec_ptp_adjtime(struct ptp_clock_info *ptp, s64 delta)
  */
 static int fec_ptp_gettime(struct ptp_clock_info *ptp, struct timespec64 *ts)
 {
-	struct fec_enet_private *adapter =
+	struct fec_enet_private *fep =
 	    container_of(ptp, struct fec_enet_private, ptp_caps);
 	u64 ns;
 	unsigned long flags;
 
-	mutex_lock(&adapter->ptp_clk_mutex);
+	spin_lock_irqsave(&fep->tmreg_lock, flags);
 	/* Check the ptp clock */
-	if (!adapter->ptp_clk_on) {
-		mutex_unlock(&adapter->ptp_clk_mutex);
+	if (!fep->ptp_clk_on) {
+		spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 		return -EINVAL;
 	}
-	spin_lock_irqsave(&adapter->tmreg_lock, flags);
-	ns = timecounter_read(&adapter->tc);
-	spin_unlock_irqrestore(&adapter->tmreg_lock, flags);
-	mutex_unlock(&adapter->ptp_clk_mutex);
+	ns = timecounter_read(&fep->tc);
+	spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 
 	*ts = ns_to_timespec64(ns);
 
@@ -404,10 +402,10 @@ static int fec_ptp_settime(struct ptp_clock_info *ptp,
 	unsigned long flags;
 	u32 counter;
 
-	mutex_lock(&fep->ptp_clk_mutex);
+	spin_lock_irqsave(&fep->tmreg_lock, flags);
 	/* Check the ptp clock */
 	if (!fep->ptp_clk_on) {
-		mutex_unlock(&fep->ptp_clk_mutex);
+		spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 		return -EINVAL;
 	}
 
@@ -417,11 +415,9 @@ static int fec_ptp_settime(struct ptp_clock_info *ptp,
 	 */
 	counter = ns & fep->cc.mask;
 
-	spin_lock_irqsave(&fep->tmreg_lock, flags);
 	writel(counter, fep->hwp + FEC_ATIME);
 	timecounter_init(&fep->tc, &fep->cc, ns);
 	spin_unlock_irqrestore(&fep->tmreg_lock, flags);
-	mutex_unlock(&fep->ptp_clk_mutex);
 	return 0;
 }
 
@@ -518,13 +514,11 @@ static void fec_time_keep(struct work_struct *work)
 	struct fec_enet_private *fep = container_of(dwork, struct fec_enet_private, time_keep);
 	unsigned long flags;
 
-	mutex_lock(&fep->ptp_clk_mutex);
+	spin_lock_irqsave(&fep->tmreg_lock, flags);
 	if (fep->ptp_clk_on) {
-		spin_lock_irqsave(&fep->tmreg_lock, flags);
 		timecounter_read(&fep->tc);
-		spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 	}
-	mutex_unlock(&fep->ptp_clk_mutex);
+	spin_unlock_irqrestore(&fep->tmreg_lock, flags);
 
 	schedule_delayed_work(&fep->time_keep, HZ);
 }
@@ -599,8 +593,6 @@ void fec_ptp_init(struct platform_device *pdev, int irq_idx)
 	}
 	fep->ptp_inc = NSEC_PER_SEC / fep->cycle_speed;
 
-	spin_lock_init(&fep->tmreg_lock);
-
 	fec_ptp_start_cyclecounter(ndev);
 
 	INIT_DELAYED_WORK(&fep->time_keep, fec_time_keep);