bcm53xx: add Tenda AC9 switch workaround

This fixes regressed support for Tenda AC9 which got broken somewhere
between LEDE 17.01 and OpenWrt 18.06.

At some point bcm47xx_nvram_gpio_pin() started working on bcm53xx
devices and it resulted in swconfig b53 performing GPIO-based switch
reset. It exposed some bug as switch stopped working.

The problem is most likely to be some missing initialization step. Tenda
AC9 comes with BCM53125 rev 4 (pretty common chip) but apparently needs
some extra quirk.

As a workaround (it doesn't make much sense to debug swconfig driver
which has a working DSA replacement) simply avoid full switch reset.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

diff --git a/target/linux/bcm53xx/patches-5.4/701-b53-add-Tenda-AC9-switch-reset-workaround.patch b/target/linux/bcm53xx/patches-5.4/701-b53-add-Tenda-AC9-switch-reset-workaround.patch
new file mode 100644 (file)
index 0000000..1b4cf5f
--- /dev/null
+++ b/target/linux/bcm53xx/patches-5.4/701-b53-add-Tenda-AC9-switch-reset-workaround.patch
@@ -0,0 +1,39 @@
+From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
+Date: Wed, 30 Jul 2025 12:37:12 +0000
+Subject: [PATCH] b53: add Tenda AC9 switch reset workaround
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+Avoid switch reset to keep it in a working state.
+
+Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
+---
+ drivers/net/phy/b53/b53_priv.h | 9 +++++++++
+ 1 file changed, 9 insertions(+)
+
+--- a/drivers/net/phy/b53/b53_priv.h
++++ b/drivers/net/phy/b53/b53_priv.h
+@@ -21,6 +21,7 @@
+ 
+ #include <linux/kernel.h>
+ #include <linux/mutex.h>
++#include <linux/of.h>
+ #include <linux/switch.h>
+ 
+ struct b53_device;
+@@ -318,6 +319,14 @@ static inline int b53_write64(struct b53
+ 
+ static inline int b53_switch_get_reset_gpio(struct b53_device *dev)
+ {
++      /*
++       * Tenda AC9 comes with gpio2=robo_reset but performing switch reset
++       * leaves it in a non-working state. It seems b53 swconfig driver misses
++       * some initialization bit.
++       */
++      if (of_machine_is_compatible("tenda,ac9"))
++              return -ENOENT;
++
+ #ifdef CONFIG_BCM47XX
+       enum bcm47xx_board board = bcm47xx_board_get();
+