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, 92 insertions, 0 deletions

diff --git a/target/linux/mvebu/patches-4.4/124-phy-improve-safety-of-fixed-phy-MII-register-reading.patch b/target/linux/mvebu/patches-4.4/124-phy-improve-safety-of-fixed-phy-MII-register-reading.patch
new file mode 100644
index 0000000000..5167b07101
--- /dev/null
+++ b/target/linux/mvebu/patches-4.4/124-phy-improve-safety-of-fixed-phy-MII-register-reading.patch
@@ -0,0 +1,92 @@
+From c36739c3cfd277a4cc9820a29dd0f4b7fbac795b Mon Sep 17 00:00:00 2001
+From: Russell King <rmk+kernel@arm.linux.org.uk>
+Date: Sun, 20 Sep 2015 18:31:36 +0100
+Subject: [PATCH 713/744] phy: improve safety of fixed-phy MII register reading
+
+There is no prevention of a concurrent call to both fixed_mdio_read()
+and fixed_phy_update_state(), which can result in the state being
+modified while it's being inspected.  Fix this by using a seqcount
+to detect modifications, and memcpy()ing the state.
+
+We remain slightly naughty here, calling link_update() and updating
+the link status within the read-side loop - which would need rework
+of the design to change.
+
+Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
+Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
+---
+ drivers/net/phy/fixed_phy.c | 28 +++++++++++++++++++++-------
+ 1 file changed, 21 insertions(+), 7 deletions(-)
+
+--- a/drivers/net/phy/fixed_phy.c
++++ b/drivers/net/phy/fixed_phy.c
+@@ -23,6 +23,7 @@
+ #include <linux/slab.h>
+ #include <linux/of.h>
+ #include <linux/gpio.h>
++#include <linux/seqlock.h>
+ 
+ #include "swphy.h"
+ 
+@@ -35,6 +36,7 @@ struct fixed_mdio_bus {
+ struct fixed_phy {
+ 	int addr;
+ 	struct phy_device *phydev;
++	seqcount_t seqcount;
+ 	struct fixed_phy_status status;
+ 	int (*link_update)(struct net_device *, struct fixed_phy_status *);
+ 	struct list_head node;
+@@ -59,13 +61,21 @@ static int fixed_mdio_read(struct mii_bu
+ 
+ 	list_for_each_entry(fp, &fmb->phys, node) {
+ 		if (fp->addr == phy_addr) {
+-			/* Issue callback if user registered it. */
+-			if (fp->link_update) {
+-				fp->link_update(fp->phydev->attached_dev,
+-						&fp->status);
+-				fixed_phy_update(fp);
+-			}
+-			return swphy_read_reg(reg_num, &fp->status);
++			struct fixed_phy_status state;
++			int s;
++
++			do {
++				s = read_seqcount_begin(&fp->seqcount);
++				/* Issue callback if user registered it. */
++				if (fp->link_update) {
++					fp->link_update(fp->phydev->attached_dev,
++							&fp->status);
++					fixed_phy_update(fp);
++				}
++				state = fp->status;
++			} while (read_seqcount_retry(&fp->seqcount, s));
++
++			return swphy_read_reg(reg_num, &state);
+ 		}
+ 	}
+ 
+@@ -117,6 +127,7 @@ int fixed_phy_update_state(struct phy_de
+ 
+ 	list_for_each_entry(fp, &fmb->phys, node) {
+ 		if (fp->addr == phydev->addr) {
++			write_seqcount_begin(&fp->seqcount);
+ #define _UPD(x) if (changed->x) \
+ 	fp->status.x = status->x
+ 			_UPD(link);
+@@ -126,6 +137,7 @@ int fixed_phy_update_state(struct phy_de
+ 			_UPD(asym_pause);
+ #undef _UPD
+ 			fixed_phy_update(fp);
++			write_seqcount_end(&fp->seqcount);
+ 			return 0;
+ 		}
+ 	}
+@@ -150,6 +162,8 @@ int fixed_phy_add(unsigned int irq, int
+ 	if (!fp)
+ 		return -ENOMEM;
+ 
++	seqcount_init(&fp->seqcount);
++
+ 	fmb->irqs[phy_addr] = irq;
+ 
+ 	fp->addr = phy_addr;