net: phy: mscc: fix deadlock in vsc85xx_default_config

The vsc85xx_default_config function called in the vsc85xx_config_init
function which is used by VSC8530, VSC8531, VSC8540 and VSC8541 PHYs
mistakenly calls phy_read and phy_write in-between phy_select_page and
phy_restore_page.

phy_select_page and phy_restore_page actually take and release the MDIO
bus lock and phy_write and phy_read take and release the lock to write
or read to a PHY register.

Let's fix this deadlock by using phy_modify_paged which handles
correctly a read followed by a write in a non-standard page.

Fixes: 6a0bfbbe ("net: phy: mscc: migrate to phy_select/restore_page functions")
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mscc.c

@@ -810,17 +810,13 @@ static int vsc85xx_default_config(struct phy_device *phydev)
 
 	phydev->mdix_ctrl = ETH_TP_MDI_AUTO;
 	mutex_lock(&phydev->lock);
-	rc = phy_select_page(phydev, MSCC_PHY_PAGE_EXTENDED_2);
-	if (rc < 0)
-		goto out_unlock;
 
-	reg_val = phy_read(phydev, MSCC_PHY_RGMII_CNTL);
-	reg_val &= ~(RGMII_RX_CLK_DELAY_MASK);
-	reg_val |= (RGMII_RX_CLK_DELAY_1_1_NS << RGMII_RX_CLK_DELAY_POS);
-	phy_write(phydev, MSCC_PHY_RGMII_CNTL, reg_val);
+	reg_val = RGMII_RX_CLK_DELAY_1_1_NS << RGMII_RX_CLK_DELAY_POS;
+
+	rc = phy_modify_paged(phydev, MSCC_PHY_PAGE_EXTENDED_2,
+			      MSCC_PHY_RGMII_CNTL, RGMII_RX_CLK_DELAY_MASK,
+			      reg_val);
 
-out_unlock:
-	rc = phy_restore_page(phydev, rc, rc > 0 ? 0 : rc);
 	mutex_unlock(&phydev->lock);
 
 	return rc;