Revert "mvebu: remove linux 4.4 support"

This reverts commit 51397d7d95d9f5e210a5557f65de1fa21e6f5921.
There are some unresolved random crashes on WRT1900AC v1 that still need
to be sorted out

Signed-off-by: Felix Fietkau <nbd@nbd.name>

1 files changed, 128 insertions, 0 deletions

diff --git a/target/linux/mvebu/patches-4.4/042-net-mvneta-Fix-race-condition-during-stopping.patch b/target/linux/mvebu/patches-4.4/042-net-mvneta-Fix-race-condition-during-stopping.patch
new file mode 100644
index 0000000000..9936ebf320
--- /dev/null
+++ b/target/linux/mvebu/patches-4.4/042-net-mvneta-Fix-race-condition-during-stopping.patch
@@ -0,0 +1,128 @@
+From: Gregory CLEMENT <gregory.clement@free-electrons.com>
+Date: Thu, 4 Feb 2016 22:09:29 +0100
+Subject: [PATCH] net: mvneta: Fix race condition during stopping
+
+When stopping the port, the CPU notifier are still there whereas the
+mvneta_stop_dev function calls mvneta_percpu_disable() on each CPUs.
+It was possible to have a new CPU coming at this point which could be
+racy.
+
+This patch adds a flag preventing executing the code notifier for a new
+CPU when the port is stopping. It also uses the spinlock introduces
+previously. To avoid the deadlock, the lock has been moved outside the
+mvneta_percpu_elect function.
+
+Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+
+--- a/drivers/net/ethernet/marvell/mvneta.c
++++ b/drivers/net/ethernet/marvell/mvneta.c
+@@ -374,6 +374,7 @@ struct mvneta_port {
+ 	 * ensuring that the configuration remains coherent.
+ 	 */
+ 	spinlock_t lock;
++	bool is_stopped;
+ 
+ 	/* Core clock */
+ 	struct clk *clk;
+@@ -2853,16 +2854,14 @@ static void mvneta_percpu_disable(void *
+ 	disable_percpu_irq(pp->dev->irq);
+ }
+ 
++/* Electing a CPU must be done in an atomic way: it should be done
++ * after or before the removal/insertion of a CPU and this function is
++ * not reentrant.
++ */
+ static void mvneta_percpu_elect(struct mvneta_port *pp)
+ {
+ 	int elected_cpu = 0, max_cpu, cpu, i = 0;
+ 
+-	/* Electing a CPU must be done in an atomic way: it should be
+-	 * done after or before the removal/insertion of a CPU and
+-	 * this function is not reentrant.
+-	 */
+-	spin_lock(&pp->lock);
+-
+ 	/* Use the cpu associated to the rxq when it is online, in all
+ 	 * the other cases, use the cpu 0 which can't be offline.
+ 	 */
+@@ -2906,7 +2905,6 @@ static void mvneta_percpu_elect(struct m
+ 		i++;
+ 
+ 	}
+-	spin_unlock(&pp->lock);
+ };
+ 
+ static int mvneta_percpu_notifier(struct notifier_block *nfb,
+@@ -2920,6 +2918,14 @@ static int mvneta_percpu_notifier(struct
+ 	switch (action) {
+ 	case CPU_ONLINE:
+ 	case CPU_ONLINE_FROZEN:
++		spin_lock(&pp->lock);
++		/* Configuring the driver for a new CPU while the
++		 * driver is stopping is racy, so just avoid it.
++		 */
++		if (pp->is_stopped) {
++			spin_unlock(&pp->lock);
++			break;
++		}
+ 		netif_tx_stop_all_queues(pp->dev);
+ 
+ 		/* We have to synchronise on tha napi of each CPU
+@@ -2957,6 +2963,7 @@ static int mvneta_percpu_notifier(struct
+ 			MVNETA_CAUSE_LINK_CHANGE |
+ 			MVNETA_CAUSE_PSC_SYNC_CHANGE);
+ 		netif_tx_start_all_queues(pp->dev);
++		spin_unlock(&pp->lock);
+ 		break;
+ 	case CPU_DOWN_PREPARE:
+ 	case CPU_DOWN_PREPARE_FROZEN:
+@@ -2981,7 +2988,9 @@ static int mvneta_percpu_notifier(struct
+ 	case CPU_DEAD:
+ 	case CPU_DEAD_FROZEN:
+ 		/* Check if a new CPU must be elected now this on is down */
++		spin_lock(&pp->lock);
+ 		mvneta_percpu_elect(pp);
++		spin_unlock(&pp->lock);
+ 		/* Unmask all ethernet port interrupts */
+ 		on_each_cpu(mvneta_percpu_unmask_interrupt, pp, true);
+ 		mvreg_write(pp, MVNETA_INTR_MISC_MASK,
+@@ -3033,7 +3042,7 @@ static int mvneta_open(struct net_device
+ 	 */
+ 	on_each_cpu(mvneta_percpu_enable, pp, true);
+ 
+-
++	pp->is_stopped = false;
+ 	/* Register a CPU notifier to handle the case where our CPU
+ 	 * might be taken offline.
+ 	 */
+@@ -3066,9 +3075,18 @@ static int mvneta_stop(struct net_device
+ {
+ 	struct mvneta_port *pp = netdev_priv(dev);
+ 
++	/* Inform that we are stopping so we don't want to setup the
++	 * driver for new CPUs in the notifiers
++	 */
++	spin_lock(&pp->lock);
++	pp->is_stopped = true;
+ 	mvneta_stop_dev(pp);
+ 	mvneta_mdio_remove(pp);
+ 	unregister_cpu_notifier(&pp->cpu_notifier);
++	/* Now that the notifier are unregistered, we can release le
++	 * lock
++	 */
++	spin_unlock(&pp->lock);
+ 	on_each_cpu(mvneta_percpu_disable, pp, true);
+ 	free_percpu_irq(dev->irq, pp->ports);
+ 	mvneta_cleanup_rxqs(pp);
+@@ -3339,7 +3357,9 @@ static int  mvneta_config_rss(struct mvn
+ 	mvreg_write(pp, MVNETA_PORT_CONFIG, val);
+ 
+ 	/* Update the elected CPU matching the new rxq_def */
++	spin_lock(&pp->lock);
+ 	mvneta_percpu_elect(pp);
++	spin_unlock(&pp->lock);
+ 
+ 	/* We have to synchronise on the napi of each CPU */
+ 	for_each_online_cpu(cpu) {