[PATCH net] net: stmmac: dwmac-rk: Ensure clk_phy doesn't contain invalid address

[Yao Zi <ziyao@disroot.org>]

We must set the clk_phy pointer to NULL to indicating it isn't available
if the optional phy clock couldn't be obtained. Otherwise the error code
returned by of_clk_get() could be wrongly taken as an address, causing
invalid pointer dereference when later clk_phy is passed to
clk_prepare_enable().

Fixes: da114122b831 ("net: ethernet: stmmac: dwmac-rk: Make the clk_phy could be used for external phy")
Signed-off-by: Yao Zi <ziyao@disroot.org>
---
 drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

On next-20250903, the fixed commit causes NULL pointer dereference on
Radxa E20C during probe of dwmac-rk, a typical dmesg looks like

[    0.273324] rk_gmac-dwmac ffbe0000.ethernet: IRQ eth_lpi not found
[    0.273888] rk_gmac-dwmac ffbe0000.ethernet: IRQ sfty not found
[    0.274520] rk_gmac-dwmac ffbe0000.ethernet: PTP uses main clock
[    0.275226] rk_gmac-dwmac ffbe0000.ethernet: clock input or output? (output).
[    0.275867] rk_gmac-dwmac ffbe0000.ethernet: Can not read property: tx_delay.
[    0.276491] rk_gmac-dwmac ffbe0000.ethernet: set tx_delay to 0x30
[    0.277026] rk_gmac-dwmac ffbe0000.ethernet: Can not read property: rx_delay.
[    0.278086] rk_gmac-dwmac ffbe0000.ethernet: set rx_delay to 0x10
[    0.278658] rk_gmac-dwmac ffbe0000.ethernet: integrated PHY? (no).
[    0.279249] Unable to handle kernel paging request at virtual address fffffffffffffffe
[    0.279948] Mem abort info:
[    0.280195]   ESR = 0x000000096000006
[    0.280523]   EC = 0x25: DABT (current EL), IL = 32 bits
[    0.280989]   SET = 0, FnV = 0
[    0.281287]   EA = 0, S1PTW = 0
[    0.281574]   FSC = 0x06: level 2 translation fault

where the invalid address is just -ENOENT (-2).

diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c
index cf619a428664..26ec8ae662a6 100644
--- a/drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c
+++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-rk.c
@@ -1414,11 +1414,17 @@ static int rk_gmac_clk_init(struct plat_stmmacenet_data *plat)
 	if (plat->phy_node) {
 		bsp_priv->clk_phy = of_clk_get(plat->phy_node, 0);
 		ret = PTR_ERR_OR_ZERO(bsp_priv->clk_phy);
-		/* If it is not integrated_phy, clk_phy is optional */
+		/*
+		 * If it is not integrated_phy, clk_phy is optional. But we must
+		 * set bsp_priv->clk_phy to NULL if clk_phy isn't proivded, or
+		 * the error code could be wrongly taken as an invalid pointer.
+		 */
 		if (bsp_priv->integrated_phy) {
 			if (ret)
 				return dev_err_probe(dev, ret, "Cannot get PHY clock\n");
 			clk_set_rate(bsp_priv->clk_phy, 50000000);
+		} else if (ret) {
+			bsp_priv->clk_phy = NULL;
 		}
 	}
 
-- 
2.50.1