[PATCH] ath79: ar8216: make switch register access atomic

[Chuanhong Guo]

reg accesses on integrated ar8229 sometimes fails. As a result, phy read
got incorrect port status and wan link goes down and up mysteriously.
After comparing ar8216 with the old driver, these local_irq_save/restore
calls are the only meaningful differences I could find and it does fix
the issue.
The same changes were added in svn r26856 by Gabor Juhos:
ar71xx: ag71xx: make switch register access atomic

As I can't find the underlying problem either, this hack is broght
back to fix the unstable link issue.
This hack is only suitable for ath79 mdio and may easily break the
driver on other platform. Limit it to ath79-only as a target patch.

Fixes: FS#2216
Fixes: FS#3226
Signed-off-by: Chuanhong Guo <gch981213 at gmail.com>
---
 .../930-ar8216-make-reg-access-atomic.patch   | 61 +++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 target/linux/ath79/patches-5.4/930-ar8216-make-reg-access-atomic.patch

diff --git a/target/linux/ath79/patches-5.4/930-ar8216-make-reg-access-atomic.patch b/target/linux/ath79/patches-5.4/930-ar8216-make-reg-access-atomic.patch
new file mode 100644
index 0000000000..42f3305195
--- /dev/null
+++ b/target/linux/ath79/patches-5.4/930-ar8216-make-reg-access-atomic.patch
@@ -0,0 +1,61 @@
+From b3797d1a92afe97c173b00fdb7824cedba24eef0 Mon Sep 17 00:00:00 2001
+From: Chuanhong Guo <gch981213 at gmail.com>
+Date: Sun, 20 Sep 2020 01:00:45 +0800
+Subject: [PATCH] ath79: ar8216: make switch register access atomic
+
+due to some unknown reason these register accesses sometimes fail
+on the integrated switch without this patch.
+
+THIS ONLY WORKS ON ATH79 AND MAY BREAK THE DRIVER ON OTHER PLATFORMS!
+The mdio bus on ath79 works in polling mode and doesn't rely on
+any interrupt. This patch breaks the driver on any mdio master
+with interrupts used.
+
+---
+--- a/drivers/net/phy/ar8216.c
++++ b/drivers/net/phy/ar8216.c
+@@ -253,12 +253,14 @@ ar8xxx_mii_write32(struct ar8xxx_priv *p
+ u32
+ ar8xxx_read(struct ar8xxx_priv *priv, int reg)
+ {
++	unsigned long flags;
+ 	struct mii_bus *bus = priv->mii_bus;
+ 	u16 r1, r2, page;
+ 	u32 val;
+ 
+ 	split_addr((u32) reg, &r1, &r2, &page);
+ 
++	local_irq_save(flags);
+ 	mutex_lock(&bus->mdio_lock);
+ 
+ 	bus->write(bus, 0x18, 0, page);
+@@ -266,6 +268,7 @@ ar8xxx_read(struct ar8xxx_priv *priv, in
+ 	val = ar8xxx_mii_read32(priv, 0x10 | r2, r1);
+ 
+ 	mutex_unlock(&bus->mdio_lock);
++	local_irq_restore(flags);
+ 
+ 	return val;
+ }
+@@ -273,11 +276,13 @@ ar8xxx_read(struct ar8xxx_priv *priv, in
+ void
+ ar8xxx_write(struct ar8xxx_priv *priv, int reg, u32 val)
+ {
++	unsigned long flags;
+ 	struct mii_bus *bus = priv->mii_bus;
+ 	u16 r1, r2, page;
+ 
+ 	split_addr((u32) reg, &r1, &r2, &page);
+ 
++	local_irq_save(flags);
+ 	mutex_lock(&bus->mdio_lock);
+ 
+ 	bus->write(bus, 0x18, 0, page);
+@@ -285,6 +290,7 @@ ar8xxx_write(struct ar8xxx_priv *priv, i
+ 	ar8xxx_mii_write32(priv, 0x10 | r2, r1, val);
+ 
+ 	mutex_unlock(&bus->mdio_lock);
++	local_irq_restore(flags);
+ }
+ 
+ u32
-- 
2.26.2