Force the internal PHY off then on when switching to the internal path.
This fixes problems where the PHY ID is not properly set.

Fixes: 7090425104db ("net: phy: add amlogic g12a mdio mux support")
Suggested-by: Qi Duan <qi.duan@amlogic.com>
Co-developed-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
---

Changes since v1:
 - Fix variable position for reverse Xmas tree requirement.

The initial discussion about this change can be found here:
https://lore.kernel.org/all/1j4jslwen5.fsf@starbuckisacylon.baylibre.com/

 drivers/net/mdio/mdio-mux-meson-g12a.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/drivers/net/mdio/mdio-mux-meson-g12a.c b/drivers/net/mdio/mdio-mux-meson-g12a.c
index 4a2e94faf57e..c4542ecf5623 100644
--- a/drivers/net/mdio/mdio-mux-meson-g12a.c
+++ b/drivers/net/mdio/mdio-mux-meson-g12a.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/delay.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/device.h>
@@ -150,6 +151,7 @@ static const struct clk_ops g12a_ephy_pll_ops = {
 
 static int g12a_enable_internal_mdio(struct g12a_mdio_mux *priv)
 {
+	u32 value;
 	int ret;
 
 	/* Enable the phy clock */
@@ -163,18 +165,25 @@ static int g12a_enable_internal_mdio(struct g12a_mdio_mux *priv)
 
 	/* Initialize ephy control */
 	writel(EPHY_G12A_ID, priv->regs + ETH_PHY_CNTL0);
-	writel(FIELD_PREP(PHY_CNTL1_ST_MODE, 3) |
-	       FIELD_PREP(PHY_CNTL1_ST_PHYADD, EPHY_DFLT_ADD) |
-	       FIELD_PREP(PHY_CNTL1_MII_MODE, EPHY_MODE_RMII) |
-	       PHY_CNTL1_CLK_EN |
-	       PHY_CNTL1_CLKFREQ |
-	       PHY_CNTL1_PHY_ENB,
-	       priv->regs + ETH_PHY_CNTL1);
+
+	/* Make sure we get a 0 -> 1 transition on the enable bit */
+	value = FIELD_PREP(PHY_CNTL1_ST_MODE, 3) |
+		FIELD_PREP(PHY_CNTL1_ST_PHYADD, EPHY_DFLT_ADD) |
+		FIELD_PREP(PHY_CNTL1_MII_MODE, EPHY_MODE_RMII) |
+		PHY_CNTL1_CLK_EN |
+		PHY_CNTL1_CLKFREQ;
+	writel(value, priv->regs + ETH_PHY_CNTL1);
 	writel(PHY_CNTL2_USE_INTERNAL |
 	       PHY_CNTL2_SMI_SRC_MAC |
 	       PHY_CNTL2_RX_CLK_EPHY,
 	       priv->regs + ETH_PHY_CNTL2);
 
+	value |= PHY_CNTL1_PHY_ENB;
+	writel(value, priv->regs + ETH_PHY_CNTL1);
+
+	/* The phy needs a bit of time to power up */
+	mdelay(10);
+
 	return 0;
 }
 
-- 
2.39.0

Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 24 Jan 2023 11:11:57 +0100 you wrote:
> Force the internal PHY off then on when switching to the internal path.
> This fixes problems where the PHY ID is not properly set.
> 
> Fixes: 7090425104db ("net: phy: add amlogic g12a mdio mux support")
> Suggested-by: Qi Duan <qi.duan@amlogic.com>
> Co-developed-by: Heiner Kallweit <hkallweit1@gmail.com>
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
> 
> [...]

Here is the summary with links:
  - [v2,net] net: mdio-mux-meson-g12a: force internal PHY off on mux switch
    https://git.kernel.org/netdev/net/c/7083df59abbc

You are awesome, thank you!
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