[PATCH] net: phy: realtek: restore RTL8211F RGMII delays on resume

[Karl Mehltretter <kmehltretter@gmail.com>]

The RTL8211F-VD loses the RGMII TX and RX delay enable bits across a
software power-down. rtl8211f_config_init() programs these bits from the
PHY interface mode, but rtl821x_resume() only clears BMCR_PDOWN and waits
for the receive clock to stabilize.

On a BeagleV Ahead configured for rgmii-id, carrier and the negotiated
speed return after an interface close/open, but the receive path does not
work. At 100 Mbit/s no frames were received. At 1000 Mbit/s all 11
observed frames had CRC errors.

Program the delays again after the existing resume delay. rtl821x_resume()
handles RTL8211F and RTL8211F-VD, both of which use
rtl8211f_config_rgmii_delay() during initialization.

Tested on a BeagleV Ahead with an RTL8211F-VD at 100 and 1000 Mbit/s,
including close/open without a link partner.

Fixes: bb726b753f75 ("net: phy: realtek: add support for RTL8211F(D)(I)-VD-CG")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
Hardware test results on BeagleV Ahead (RTL8211F-VD, rgmii-id):

                               baseline          patched
 100 Mbit/s close/open         RX silent         pass
 1000 Mbit/s close/open        11/11 CRC errors  pass
 no-link close/open, reconnect 15/15 CRC errors  pass

The patched kernel also passed bidirectional 1 MiB SHA-256 transfers at
100 and 1000 Mbit/s and eight consecutive 1000 Mbit/s close/open cycles,
all without RX CRC errors. An s2idle suspend/resume test passed on both
kernels and did not reproduce the bug.

Built with ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- LLVM=1.

 drivers/net/phy/realtek/realtek_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/realtek/realtek_main.c b/drivers/net/phy/realtek/realtek_main.c
index 177b62a7b..c867e5213 100644
--- a/drivers/net/phy/realtek/realtek_main.c
+++ b/drivers/net/phy/realtek/realtek_main.c
@@ -1375,7 +1375,7 @@ static int rtl821x_resume(struct phy_device *phydev)
 
 	msleep(20);
 
-	return 0;
+	return rtl8211f_config_rgmii_delay(phydev);
 }
 
 static int rtl8211f_resume(struct phy_device *phydev)
-- 
2.54.0