Re: [PATCH] net: fec: defer probe if PHY on external MDIO bus is not available

On some SoCs like i.MX6UL it is common to use the same MDIO bus for PHYs
on both Ethernet controllers. Currently device trees for such setups
have to make assumptions regarding the probe order of the controllers:

For example in imx6ul-14x14-evk.dtsi, the MDIO bus of fec2 is used for
the PHYs of both fec1 and fec2. The reason is that fec2 has a lower
address than fec1 and is thus loaded first, so the bus is already
available when fec1 is probed.

Besides being confusing, this limitation also makes it impossible to use
the same device tree for variants of the i.MX6UL with one Ethernet
controller (which have to use the MDIO of fec1, as fec2 does not exist)
and variants with two controllers (which have to use fec2 because of the
load order).

To fix this, defer the probe of the Ethernet controller when the PHY is
not on our own MDIO bus and not available.

Signed-off-by: Matthias Schiffer <redacted>
---
 drivers/net/ethernet/freescale/fec_main.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 47a6fc702ac7..dc070dd216e8 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c

@@ -3820,7 +3820,28 @@ fec_probe(struct platform_device *pdev)
 		goto failed_stop_mode;
 
 	phy_node = of_parse_phandle(np, "phy-handle", 0);
-	if (!phy_node && of_phy_is_fixed_link(np)) {
+	if (phy_node) {
+		struct device_node *mdio_parent =
+			of_get_next_parent(of_get_parent(phy_node));
+
+		ret = 0;
+
+		/* Skip PHY availability check for our own MDIO bus to avoid
+		 * cyclic dependency
+		 */
+		if (mdio_parent != np) {
+			struct phy_device *phy = of_phy_find_device(phy_node);
+
+			if (phy)
+				put_device(&phy->mdio.dev);
+			else
+				ret = -EPROBE_DEFER;
+		}