kernel: net: phy: realtek: improve RealTek 2.5G PHY driver

 * use interface mode switching only when operating in C45 mode
   Linux prevents switching the interface mode when using C22 MDIO,
   hence use rate-adapter mode in case the PHY controlled via C22.

 * use phy_read_paged where appropriate

 * use existing generic inline functions to handle 10GbE advertisements
   instead of redundantly defining register macros in realtek.c which
   are not actually vendor-specific.

 * make sure 10GbE advertisement is valid, preventing false-positive
   warning "Downshift occurred from negotiated speed 2.5Gbps to actual
   speed 1Gbps, check cabling!" with some link-partners using 1G mode.

 * Support Link Down Power Saving Mode (ALDPS)

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/target/linux/generic/pending-5.15/726-net-phy-realtek-use-phy_read_paged-instead-of-open-c.patch b/target/linux/generic/pending-5.15/726-net-phy-realtek-use-phy_read_paged-instead-of-open-c.patch
new file mode 100644
index 0000000000..250436ff39
--- /dev/null
+++ b/target/linux/generic/pending-5.15/726-net-phy-realtek-use-phy_read_paged-instead-of-open-c.patch
@@ -0,0 +1,27 @@
+From 934cdd67e7cf71f97a2a8aea2892e540af47dcdf Mon Sep 17 00:00:00 2001
+From: Daniel Golle <daniel@makrotopia.org>
+Date: Sat, 22 Apr 2023 01:21:14 +0100
+Subject: [PATCH 1/3] net: phy: realtek: use phy_read_paged instead of open
+ coding
+
+Instead of open coding a paged read, use the phy_read_paged function
+in rtlgen_supports_2_5gbps.
+
+Signed-off-by: Daniel Golle <daniel@makrotopia.org>
+---
+ drivers/net/phy/realtek.c | 4 +---
+ 1 file changed, 1 insertion(+), 3 deletions(-)
+
+--- a/drivers/net/phy/realtek.c
++++ b/drivers/net/phy/realtek.c
+@@ -727,9 +727,7 @@ static bool rtlgen_supports_2_5gbps(stru
+ {
+ 	int val;
+ 
+-	phy_write(phydev, RTL821x_PAGE_SELECT, 0xa61);
+-	val = phy_read(phydev, 0x13);
+-	phy_write(phydev, RTL821x_PAGE_SELECT, 0);
++	val = phy_read_paged(phydev, 0xa61, 0x13);
+ 
+ 	return val >= 0 && val & RTL_SUPPORTS_2500FULL;
+ }